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Sample records for michaelis-menten uptake kinetics

  1. Reexamining Michaelis-Menten Enzyme Kinetics for Xanthine Oxidase

    Science.gov (United States)

    Bassingthwaighte, James B.; Chinn, Tamara M.

    2013-01-01

    Abbreviated expressions for enzyme kinetic expressions, such as the Michaelis-Menten (M-M) equations, are based on the premise that enzyme concentrations are low compared with those of the substrate and product. When one does progress experiments, where the solute is consumed during conversion to form a series of products, the idealized conditions…

  2. Classical Michaelis-Menten and system theory approach to modeling metabolite formation kinetics.

    Science.gov (United States)

    Popović, Jovan

    2004-01-01

    When single doses of drug are administered and kinetics are linear, techniques, which are based on the compartment approach and the linear system theory approach, in modeling the formation of the metabolite from the parent drug are proposed. Unlike the purpose-specific compartment approach, the methodical, conceptual and computational uniformity in modeling various linear biomedical systems is the dominant characteristic of the linear system approach technology. Saturation of the metabolic reaction results in nonlinear kinetics according to the Michaelis-Menten equation. The two compartment open model with Michaelis-Menten elimination kinetics is theorethicaly basic when single doses of drug are administered. To simulate data or to fit real data using this model, one must resort to numerical integration. A biomathematical model for multiple dosage regimen calculations of nonlinear metabolic systems in steady-state and a working example with phenytoin are presented. High correlation between phenytoin steady-state serum levels calculated from individual Km and Vmax values in the 15 adult epileptic outpatients and the observed levels at the third adjustment of phenytoin daily dose (r=0.961, p<0.01) were found.

  3. Diffusion influence on Michaelis Menten kinetics: II. The low substrate concentration limit

    Science.gov (United States)

    Kim, Hyojoon; Shin, Kook Joe

    2007-02-01

    The diffusion-influenced Michaelis-Menten kinetics in the low substrate concentration limit is studied in one and three dimensions. For the initial pair distribution of enzyme and substrate, we obtain the exact analytical results. We find that at short times the diffusion effect can make the reaction rate faster. The concentration deviations of the substrate and enzyme show t-1/2 and t-3/2 power-law behaviours in one and three dimensions, respectively, at long times. On the other hand, the average lifetime of the intermediate is independent of the initial state in one dimension, while it depends on the initial state in three dimensions. The ultimate production yield approaches unity in one dimension but it reaches a different value depending on other parameters in three dimensions. We also obtain the analytical results for the initial random distribution.

  4. Diffusion influence on Michaelis-Menten kinetics: II. The low substrate concentration limit

    International Nuclear Information System (INIS)

    Kim, Hyojoon; Shin, Kook Joe

    2007-01-01

    The diffusion-influenced Michaelis-Menten kinetics in the low substrate concentration limit is studied in one and three dimensions. For the initial pair distribution of enzyme and substrate, we obtain the exact analytical results. We find that at short times the diffusion effect can make the reaction rate faster. The concentration deviations of the substrate and enzyme show t -1/2 and t -3/2 power-law behaviours in one and three dimensions, respectively, at long times. On the other hand, the average lifetime of the intermediate is independent of the initial state in one dimension, while it depends on the initial state in three dimensions. The ultimate production yield approaches unity in one dimension but it reaches a different value depending on other parameters in three dimensions. We also obtain the analytical results for the initial random distribution

  5. Stability estimation of autoregulated genes under Michaelis-Menten-type kinetics

    Science.gov (United States)

    Arani, Babak M. S.; Mahmoudi, Mahdi; Lahti, Leo; González, Javier; Wit, Ernst C.

    2018-06-01

    Feedback loops are typical motifs appearing in gene regulatory networks. In some well-studied model organisms, including Escherichia coli, autoregulated genes, i.e., genes that activate or repress themselves through their protein products, are the only feedback interactions. For these types of interactions, the Michaelis-Menten (MM) formulation is a suitable and widely used approach, which always leads to stable steady-state solutions representative of homeostatic regulation. However, in many other biological phenomena, such as cell differentiation, cancer progression, and catastrophes in ecosystems, one might expect to observe bistable switchlike dynamics in the case of strong positive autoregulation. To capture this complex behavior we use the generalized family of MM kinetic models. We give a full analysis regarding the stability of autoregulated genes. We show that the autoregulation mechanism has the capability to exhibit diverse cellular dynamics including hysteresis, a typical characteristic of bistable systems, as well as irreversible transitions between bistable states. We also introduce a statistical framework to estimate the kinetics parameters and probability of different stability regimes given observational data. Empirical data for the autoregulated gene SCO3217 in the SOS system in Streptomyces coelicolor are analyzed. The coupling of a statistical framework and the mathematical model can give further insight into understanding the evolutionary mechanisms toward different cell fates in various systems.

  6. Biphasic character of ribosomal translocation and non-Michaelis-Menten kinetics of translation

    Science.gov (United States)

    Xie, Ping

    2014-12-01

    We study theoretically the kinetics of mRNA translocation in the wild-type (WT) Escherichia coli ribosome, which is composed of a small 30 S and large 50 S subunit, and the ribosomes with mutations to some intersubunit bridges such as B1a, B4, B7a, and B8. The theoretical results reproduce well the available in vitro experimental data on the biphasic kinetics of the forward mRNA translocation catalyzed by elongation factor G (EF-G) hydrolyzing GTP, which can be best fit by the sum of two exponentials, and the monophasic kinetics of the spontaneous reverse mRNA translocation in the absence of the elongation factor, which can be best fit by a single-exponential function, in both the WT and mutant ribosomes. We show that both the mutation-induced increase in the maximal rate of the slow phase for the forward mRNA translocation and that in the rate of the spontaneous reverse mRNA translocation result from a reduction in the intrinsic energy barrier to resist the rotational movements between the two subunits, giving the same degree of increase in the two rates. The mutation-induced increase in the maximal rate of the fast phase for the forward mRNA translocation results mainly from the increase in the rate of the ribosomal unlocking, a conformational change in the ribosome that widens the mRNA channel for the mRNA translocation to take place, which could be partly due to the effect of the mutation on the intrasubunit 30S head rotation. Moreover, we study the translation rate of the WT and mutant ribosomes. It is shown that the translation rate versus the concentration of EF-G-GTP does not follow the Michaelis-Menten (MM) kinetics, which is in sharp contrast to the general property of other enzymes that the rate of the enzymatic reaction versus the concentration of a substrate follows the MM kinetics. The physical origin of this non-MM kinetics for the ribosome is revealed.

  7. Use of Mushroom Tyrosinase to Introduce Michaelis-Menten Enzyme Kinetics to Biochemistry Students

    Science.gov (United States)

    Flurkey, William H.; Inlow, Jennifer K.

    2017-01-01

    An inexpensive enzyme kinetics laboratory exercise for undergraduate biochemistry students is described utilizing tyrosinase from white button mushrooms. The exercise can be completed in one or two three-hour lab sessions. The optimal amounts of enzyme, substrate (catechol), and inhibitor (kojic acid) are first determined, and then kinetic data is…

  8. Occurrence of dead core in catalytic particles containing immobilized enzymes: analysis for the Michaelis-Menten kinetics and assessment of numerical methods.

    Science.gov (United States)

    Pereira, Félix Monteiro; Oliveira, Samuel Conceição

    2016-11-01

    In this article, the occurrence of dead core in catalytic particles containing immobilized enzymes is analyzed for the Michaelis-Menten kinetics. An assessment of numerical methods is performed to solve the boundary value problem generated by the mathematical modeling of diffusion and reaction processes under steady state and isothermal conditions. Two classes of numerical methods were employed: shooting and collocation. The shooting method used the ode function from Scilab software. The collocation methods included: that implemented by the bvode function of Scilab, the orthogonal collocation, and the orthogonal collocation on finite elements. The methods were validated for simplified forms of the Michaelis-Menten equation (zero-order and first-order kinetics), for which analytical solutions are available. Among the methods covered in this article, the orthogonal collocation on finite elements proved to be the most robust and efficient method to solve the boundary value problem concerning Michaelis-Menten kinetics. For this enzyme kinetics, it was found that the dead core can occur when verified certain conditions of diffusion-reaction within the catalytic particle. The application of the concepts and methods presented in this study will allow for a more generalized analysis and more accurate designs of heterogeneous enzymatic reactors.

  9. Determination of the Michaelis-Menten kinetics and the genes expression involved in phyto-degradation of cyanide and ferri-cyanide.

    Science.gov (United States)

    Yu, Xiao-Zhang; Zhang, Xue-Hong

    2016-07-01

    Hydroponic experiments were conducted with different species of plants (rice, maize, soybean and willow) exposed to ferri-cyanide to investigate the half-saturation constant (K M ) and the maximal metabolic capacity (v max ) involved in phyto-assimilation. Three varieties for each testing species were collected from different origins. Measured concentrations show that the uptake rates responded biphasically to ferri-cyanide treatments by showing increases linearly at low and almost constant at high concentrations from all treatments, indicating that phyto-assimilation of ferri-cyanide followed the Michaelis-Menten kinetics. Using non-linear regression, the highest v max was by rice, followed by willows. The lowest v max was found for soybean. All plants, except maize (DY26) and rice (XJ12), had a similar K M value, suggesting the same enzyme was active in phyto-assimilation of ferri-cyanide. Transcript level, by real-time quantitative PCR, of enzymes involved in degradation of cyanides showed that the analyzed genes were differently expressed during different cyanides exposure. The expression of CAS and ST genes responded positively to KCN exposure, suggesting that β-CAS and ST pathways were two possible pathways for cyanide detoxification in rice. The transcript level of NIT and ASPNASE genes also showed a remarkable up-regulation to KCN, implying the contribution to the pool of amino acid aspartate, which is an end product of CN metabolism. Up-regulation of GS genes suggests that acquisition of ammonium released from cyanide degradation may be an additional nitrogen source for plant nutrition. Results also revealed that the expressions of these genes, except for GS, were relatively constant during iron cyanide exposure, suggesting that they are likely metabolized by plants through a non-defined pathway rather than the β-CAS pathway.

  10. Utilization of integrated Michaelis-Menten equations for enzyme inhibition diagnosis and determination of kinetic constants using Solver supplement of Microsoft Office Excel.

    Science.gov (United States)

    Bezerra, Rui M F; Fraga, Irene; Dias, Albino A

    2013-01-01

    Enzyme kinetic parameters are usually determined from initial rates nevertheless, laboratory instruments only measure substrate or product concentration versus reaction time (progress curves). To overcome this problem we present a methodology which uses integrated models based on Michaelis-Menten equation. The most severe practical limitation of progress curve analysis occurs when the enzyme shows a loss of activity under the chosen assay conditions. To avoid this problem it is possible to work with the same experimental points utilized for initial rates determination. This methodology is illustrated by the use of integrated kinetic equations with the well-known reaction catalyzed by alkaline phosphatase enzyme. In this work nonlinear regression was performed with the Solver supplement (Microsoft Office Excel). It is easy to work with and track graphically the convergence of SSE (sum of square errors). The diagnosis of enzyme inhibition was performed according to Akaike information criterion. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  11. Dynamic disorder in single-molecule Michaelis-Menten kinetics: The reaction-diffusion formalism in the Wilemski-Fixman approximation

    Science.gov (United States)

    Chaudhury, Srabanti; Cherayil, Binny J.

    2007-09-01

    Single-molecule equations for the Michaelis-Menten [Biochem. Z. 49, 333 (1913)] mechanism of enzyme action are analyzed within the Wilemski-Fixman [J. Chem. Phys. 58, 4009 (1973); 60, 866 (1974)] approximation after the effects of dynamic disorder—modeled by the anomalous diffusion of a particle in a harmonic well—are incorporated into the catalytic step of the reaction. The solution of the Michaelis-Menten equations is used to calculate the distribution of waiting times between successive catalytic turnovers in the enzyme β-galactosidase. The calculated distribution is found to agree qualitatively with experimental results on this enzyme obtained at four different substrate concentrations. The calculations are also consistent with measurements of correlations in the fluctuations of the fluorescent light emitted during the course of catalysis, and with measurements of the concentration dependence of the randomness parameter.

  12. The Michaelis-Menten-Stueckelberg Theorem

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    Alexander N. Gorban

    2011-05-01

    Full Text Available We study chemical reactions with complex mechanisms under two assumptions: (i intermediates are present in small amounts (this is the quasi-steady-state hypothesis or QSS and (ii they are in equilibrium relations with substrates (this is the quasiequilibrium hypothesis or QE. Under these assumptions, we prove the generalized mass action law together with the basic relations between kinetic factors, which are sufficient for the positivity of the entropy production but hold even without microreversibility, when the detailed balance is not applicable. Even though QE and QSS produce useful approximations by themselves, only the combination of these assumptions can render the possibility beyond the “rarefied gas” limit or the “molecular chaos” hypotheses. We do not use any a priori form of the kinetic law for the chemical reactions and describe their equilibria by thermodynamic relations. The transformations of the intermediate compounds can be described by the Markov kinetics because of their low density (low density of elementary events. This combination of assumptions was introduced by Michaelis and Menten in 1913. In 1952, Stueckelberg used the same assumptions for the gas kinetics and produced the remarkable semi-detailed balance relations between collision rates in the Boltzmann equation that are weaker than the detailed balance conditions but are still sufficient for the Boltzmann H-theorem to be valid. Our results are obtained within the Michaelis-Menten-Stueckelbeg conceptual framework.

  13. Real-Time Enzyme Kinetics by Quantitative NMR Spectroscopy and Determination of the Michaelis-Menten Constant Using the Lambert-W Function

    Science.gov (United States)

    Her, Cheenou; Alonzo, Aaron P.; Vang, Justin Y.; Torres, Ernesto; Krishnan, V. V.

    2015-01-01

    Enzyme kinetics is an essential part of a chemistry curriculum, especially for students interested in biomedical research or in health care fields. Though the concept is routinely performed in undergraduate chemistry/biochemistry classrooms using other spectroscopic methods, we provide an optimized approach that uses a real-time monitoring of the…

  14. Exact and approximate solutions for the decades-old Michaelis-Menten equation: Progress-curve analysis through integrated rate equations.

    Science.gov (United States)

    Goličnik, Marko

    2011-01-01

    The Michaelis-Menten rate equation can be found in most general biochemistry textbooks, where the time derivative of the substrate is a hyperbolic function of two kinetic parameters (the limiting rate V, and the Michaelis constant K(M) ) and the amount of substrate. However, fundamental concepts of enzyme kinetics can be difficult to understand fully, or can even be misunderstood, by students when based only on the differential form of the Michaelis-Menten equation, and the variety of methods available to calculate the kinetic constants from rate versus substrate concentration "textbook data." Consequently, enzyme kinetics can be confusing if an analytical solution of the Michaelis-Menten equation is not available. Therefore, the still rarely known exact solution to the Michaelis-Menten equation is presented here through the explicit closed-form equation in terms of the Lambert W(x) function. Unfortunately, as the W(x) is not available in standard curve-fitting computer programs, the practical use of this direct solution is limited for most life-science students. Thus, the purpose of this article is to provide analytical approximations to the equation for modeling Michaelis-Menten kinetics. The elementary and explicit nature of these approximations can provide students with direct and simple estimations of kinetic parameters from raw experimental time-course data. The Michaelis-Menten kinetics studied in the latter context can provide an ideal alternative to the 100-year-old problems of data transformation, graphical visualization, and data analysis of enzyme-catalyzed reactions. Hence, the content of the course presented here could gradually become an important component of the modern biochemistry curriculum in the 21st century. Copyright © 2011 Wiley Periodicals, Inc.

  15. More Nuts and Bolts of Michaelis-Menten Enzyme Kinetics

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    Lechner, Joseph H.

    2011-01-01

    Several additions to a classroom activity are proposed in which an "enzyme" (the student) converts "substrates" (nut-bolt assemblies) into "products" (separated nuts and bolts) by unscrewing them. (Contains 1 table.)

  16. Michaelis - Menten equation for degradation of insoluble substrate

    DEFF Research Database (Denmark)

    Andersen, Morten; Kari, Jeppe; Borch, Kim

    2017-01-01

    substrate it is difficult to assess whether the requirement of the MM equation is met. In this paper we study a simple kinetic model, where removal of attack sites expose new ones which preserve the total accessible substrate, and denote this approach the substrate conserving model. The kinetic equations...... are solved in closed form, both steady states and progress curves, for any admissible values of initial conditions and rate constants. The model is shown to merge with the MM equation and the reverse MM equation when these are valid. The relation between available molar concentration of attack sites and mass...

  17. Stability in a Simple Food Chain System with Michaelis-Menten Functional Response and Nonlocal Delays

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    Wenzhen Gan

    2013-01-01

    Full Text Available This paper is concerned with the asymptotical behavior of solutions to the reaction-diffusion system under homogeneous Neumann boundary condition. By taking food ingestion and species' moving into account, the model is further coupled with Michaelis-Menten type functional response and nonlocal delay. Sufficient conditions are derived for the global stability of the positive steady state and the semitrivial steady state of the proposed problem by using the Lyapunov functional. Our results show that intraspecific competition benefits the coexistence of prey and predator. Furthermore, the introduction of Michaelis-Menten type functional response positively affects the coexistence of prey and predator, and the nonlocal delay is harmless for stabilities of all nonnegative steady states of the system. Numerical simulations are carried out to illustrate the main results.

  18. Modeling uptake kinetics of cadmium by field-grown lettuce

    Energy Technology Data Exchange (ETDEWEB)

    Chen Weiping [Department of Environmental Sciences, University of California, 900 University Avenue, Riverside, CA 92521 (United States)], E-mail: chenweip@yahoo.com.cn; Li Lianqing [Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Nanjing 210095 (China); Chang, Andrew C.; Wu Laosheng [Department of Environmental Sciences, University of California, 900 University Avenue, Riverside, CA 92521 (United States); Kwon, Soon-Ik [Agricultural Environmental and Ecology Division, National Institute of Agricultural Science and Technology, Suwon 441-707 (Korea, Republic of); Bottoms, Rick [Desert Research and Extension Center, 1004 East Holton Road, El Centro, CA 92243 (United States)

    2008-03-15

    Cadmium uptake by field grown Romaine lettuce treated with P-fertilizers of different Cd levels was investigated over an entire growing season. Results indicated that the rate of Cd uptake at a given time of the season can be satisfactorily described by the Michaelis-Menten kinetics, that is, plant uptake increases as the Cd concentration in soil solution increases, and it gradually approaches a saturation level. However, the rate constant of the Michaelis-Menten kinetics changes over the growing season. Under a given soil Cd level, the cadmium content in plant tissue decreases exponentially with time. To account for the dynamic nature of Cd uptake, a kinetic model integrating the time factor was developed to simulate Cd plant uptake over the growing season: C{sub Plant} = C{sub Solution} . PUF{sub max} . exp[-b . t], where C{sub Plant} and C{sub Solution} refer to the Cd content in plant tissue and soil solution, respectively, PUF{sub max} and b are kinetic constants. - A kinetic model was developed to evaluate the uptake of Cd under field conditions.

  19. Modeling uptake kinetics of cadmium by field-grown lettuce

    International Nuclear Information System (INIS)

    Chen Weiping; Li Lianqing; Chang, Andrew C.; Wu Laosheng; Kwon, Soon-Ik; Bottoms, Rick

    2008-01-01

    Cadmium uptake by field grown Romaine lettuce treated with P-fertilizers of different Cd levels was investigated over an entire growing season. Results indicated that the rate of Cd uptake at a given time of the season can be satisfactorily described by the Michaelis-Menten kinetics, that is, plant uptake increases as the Cd concentration in soil solution increases, and it gradually approaches a saturation level. However, the rate constant of the Michaelis-Menten kinetics changes over the growing season. Under a given soil Cd level, the cadmium content in plant tissue decreases exponentially with time. To account for the dynamic nature of Cd uptake, a kinetic model integrating the time factor was developed to simulate Cd plant uptake over the growing season: C Plant = C Solution . PUF max . exp[-b . t], where C Plant and C Solution refer to the Cd content in plant tissue and soil solution, respectively, PUF max and b are kinetic constants. - A kinetic model was developed to evaluate the uptake of Cd under field conditions

  20. Why plankton modellers should reconsider using rectangular hyperbolic (Michaelis-Menten, Monod descriptions of predator-prey interactions

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    Kevin John Flynn

    2016-09-01

    Full Text Available Rectangular hyperbolic type 2 (RHt2; Michaelis-Menten or Monod -like functions are commonly used to describe predation kinetics in plankton models, either alone or together with a prey selectivity algorithm deploying the same half-saturation constant for all prey types referenced to external prey biomass abundance. We present an analysis that indicates that such descriptions are liable to give outputs that are not plausible according to encounter theory. This is especially so for multi-prey type applications or where changes are made to the maximum feeding rate during a simulation. The RHt2 approach also gives no or limited potential for descriptions of events such as true de-selection of prey, effects of turbulence on encounters, or changes in grazer motility with satiation. We present an alternative, which carries minimal parameterisation effort and computational cost, linking allometric algorithms relating prey abundance and encounter rates to a prey-selection function controlled by satiation. The resultant Satiation-Controlled-Encounter-Based (SCEB function provides a flexible construct describing numeric predator-prey interactions with biomass-feedback control of grazing. The SCEB function includes an attack component similar to that in the Holling disk equation but SCEB differs in having only a single (satiation-based handling constant and an explicit maximum grazing rate. We argue that there is no justification for continuing to deploy RHt2 functions to describe plankton predator-prey interactions.

  1. Nonthermal effect of microwave irradiation on nitrite uptake in Chlamydomonas reinhardtii

    International Nuclear Information System (INIS)

    Pedrajas, C.; Cotrino, J.

    1989-01-01

    When cells of the unicellular green alga Chlamydomonas reinhardtii were subjected to microwave irradiation at 2.45 GHz, nitrite uptake kinetics still obeyed the Michaelis-Menten equation, the Km of the process remaining constant, whereas V max increased, which indicates an enhanced nonthermal permeability in irradiated cells. (author)

  2. Patterns induced by super cross-diffusion in a predator-prey system with Michaelis-Menten type harvesting.

    Science.gov (United States)

    Liu, Biao; Wu, Ranchao; Chen, Liping

    2018-04-01

    Turing instability and pattern formation in a super cross-diffusion predator-prey system with Michaelis-Menten type predator harvesting are investigated. Stability of equilibrium points is first explored with or without super cross-diffusion. It is found that cross-diffusion could induce instability of equilibria. To further derive the conditions of Turing instability, the linear stability analysis is carried out. From theoretical analysis, note that cross-diffusion is the key mechanism for the formation of spatial patterns. By taking cross-diffusion rate as bifurcation parameter, we derive amplitude equations near the Turing bifurcation point for the excited modes by means of weakly nonlinear theory. Dynamical analysis of the amplitude equations interprets the structural transitions and stability of various forms of Turing patterns. Furthermore, the theoretical results are illustrated via numerical simulations. Copyright © 2018. Published by Elsevier Inc.

  3. At the centennial of Michaelis and Menten, competing Michaelis-Menten steps explain effect of GLP-1 on blood-brain transfer and metabolism of glucose.

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    Gejl, Michael; Rungby, Jørgen; Brock, Birgitte; Gjedde, Albert

    2014-08-01

    Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic incretin hormone with both pancreatic and extrapancreatic effects. Studies of GLP-1 reveal significant effects in regions of brain tissue that regulate appetite and satiety. GLP-1 mimetics are used for the treatment of type 2 diabetes mellitus. GLP-1 interacts with peripheral functions in which the autonomic nervous system plays an important role, and emerging pre-clinical findings indicate a potential neuroprotective role of the peptide, for example in models of stroke and in neurodegenerative disorders. A century ago, Leonor Michaelis and Maud Menten described the steady-state enzyme kinetics that still apply to the multiple receptors, transporters and enzymes that define the biochemical reactions of the brain, including the glucose-dependent impact of GLP-1 on blood-brain glucose transfer and metabolism. This MiniReview examines the potential of GLP-1 as a molecule of interest for the understanding of brain energy metabolism and with reference to the impact on brain metabolism related to appetite and satiety regulation, stroke and neurodegenerative disorders. These effects can be understood only by reference to the original formulation of the Michaelis-Menten equation as applied to a chain of kinetically controlled steps. Indeed, the effects of GLP-1 receptor activation on blood-brain glucose transfer and brain metabolism of glucose depend on the glucose concentration and relative affinities of the steps both in vitro and in vivo, as in the pancreas. © 2014 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).

  4. Modelling the extra and intracellular uptake and discharge of heavy metals in Fontinalis antipyretica transplanted along a heavy metal and pH contamination gradient

    International Nuclear Information System (INIS)

    Fernandez, J.A.; Vazquez, M.D.; Lopez, J.; Carballeira, A.

    2006-01-01

    Samples of the aquatic bryophyte Fontinalis antipyretica Hedw. were transplanted to different sites with the aim of characterizing the kinetics of the uptake and discharge of heavy metals in the extra and intracellular compartments. The accumulation of metals in extracellular compartments, characterized by an initial rapid accumulation, then a gradual slowing down over time, fitted perfectly to a Michaelis-Menten model. The discharge of metals from the same compartment followed an inverse linear model or an inverse Michaelis-Menten model, depending on the metal. In intracellular sites both uptake and discharge occurred more slowly and progressively, following a linear model. We also observed that the acidity of the environment greatly affected metal accumulation in extracellular sites, even when the metals were present at relatively high concentrations, whereas the uptake of metals within cells was much less affected by pH. - The kinetics of uptake and discharge of heavy metals, in different cellular locations, were studied in transplanted aquatic mosses

  5. Complex dynamics of a stochastic discrete modified Leslie-Gower predator-prey model with Michaelis-Menten type prey harvesting

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    A. Elhassanein

    2014-06-01

    Full Text Available This paper introduced a stochastic discretized version of the modified Leslie-Gower predator-prey model with Michaelis-Menten type prey harvesting. The dynamical behavior of the proposed model was investigated. The existence and stability of the equilibria of the skeleton were studied. Numerical simulations were employed to show the model's complex dynamics by means of the largest Lyapunov exponents, bifurcations, time series diagrams and phase portraits. The effects of noise intensity on its dynamics and the intermittency phenomenon were also discussed via simulation.

  6. Continuous ammonium enrichment of a woodland stream: uptake kinetics, leaf decomposition, and nitrification

    Energy Technology Data Exchange (ETDEWEB)

    Newbold, J D; Elwood, J W; Schulze, M S; Stark, R W; Barmeier, J C

    1983-01-01

    In order to test for nitrogen limitation and examine ammonium uptake by stream sediments, ammonium hydroxide was added continuously at concentrations averaging 100 /sup +/gl/sup -1/ for 70 days to a second-order reach of Walker Branch, an undisturbed woodland stream in Tennessee. Ammonium uptake during the first 4 h of addition corresponded to adsorption kinetics rather than to first-order uptake or to Michaelis-Menten kinetics. However, the calculated adsorption partition coefficient was two to four orders of magnitude greater than values reported for physical adsorption of ammonium, suggesting that the uptake was largely biotic. Mass balance indicated that the uptake of ammonium from the water could be accounted for by increased nitrogen content in benthic organic detritus. Nitrification, inferred from longitudinal gradients in NO/sub 3/, began soon after enrichment and increased dramatically near the end of the experiment. Both ammonium and nitrate concentrations dropped quickly to near background levels when input ceased, indicating little desorption or nitrification of excess nitrogen stored in the reach. There was no evidence of nitrogen limitation as measured by weight loss, oxygen consumption, phosphorus content, and macroinvertebrate density of red oak leaf packs, or by chlorophyll content and aufwuchs biomass on plexiglass slides. A continuous phosphorus enrichment 1 year earlier had demonstrated phosphorus limitation in Walker Branch. 38 references, 6 figures, 3 tables.

  7. [Kinetics of uptake of phosphates and nitrates by marine multicellular algae Gelidium latifolium (Grev.) Born. et Thur].

    Science.gov (United States)

    Silkin, V A; Chubchikova, I N

    2007-01-01

    We studied nonstationary kinetics of the uptake of phosphates and nitrates by the red marine algae Gelidium latifolium (Grev.) Born et Thur. and calculated constants of the Michaelis-Menten equation for these elements. In the area of 0-3 microM, the kinetics of phosphate consumption had the following coefficients: maximum rate of uptake 0.8 micromol/(g x h), constant of half-saturation 1.745 microM. For nitrate nitrogen at 0-30 microM, an adaptive strategy of uptake kinetics was noted with change of the equation parameters with time: after 1 h, the maximum rate of uptake was 5.1 micromol/(g x h) and constant of half-saturation 19 gM, while within 2 h, the maximum rate of uptake significantly increased. This could be related to the synthesis of nitrate reductase. Coupled with the uptake of nitrates, nonstationary kinetics of the release of nitrates in the surrounding medium had a one-peak pattern: the maximum concentration of nitrites in the medium and the time of its achievement increased with the initial concentration of nitrates. The maximum concentration of nitrites was 6 to 14% of the initial concentration in the medium.

  8. Kinetics of glucose transport in rat muscle

    DEFF Research Database (Denmark)

    Ploug, Thorkil; Galbo, Henrik; Vinten, Jørgen

    1987-01-01

    The effects of insulin and prior muscle contractions, respectively, on 3-O-methylglucose (3-O-MG) transport in skeletal muscle were studied in the perfused rat hindquarter. Initial rates of entry of 3-O-MG in red gastrocnemius, soleus, and white gastrocnemius muscles as a function of perfusate 3-O-MG...... concentration exhibited Michaelis-Menten kinetics. Uptake by simple diffusion could not be detected. The maximum 3-O-MG transport velocity (Vmax) was increased more by maximum isometric contractions (10- to 40-fold, depending on fiber type) than by insulin (20,000 microU/ml; 3- to 20-fold) in both red and white...

  9. Stoichiometry and kinetics of single and mixed substrate uptake in Aspergillus niger.

    Science.gov (United States)

    Lameiras, Francisca; Ras, Cor; Ten Pierick, Angela; Heijnen, Joseph J; van Gulik, Walter M

    2018-02-01

    In its natural environment, the filamentous fungus Aspergillus niger grows on decaying fruits and plant material, thereby enzymatically degrading the lignocellulosic constituents (lignin, cellulose, hemicellulose, and pectin) into a mixture of mono- and oligosaccharides. To investigate the kinetics and stoichiometry of growth of this fungus on lignocellulosic sugars, we carried out batch cultivations on six representative monosaccharides (glucose, xylose, mannose, rhamnose, arabinose, and galacturonic acid) and a mixture of these. Growth on these substrates was characterized in terms of biomass yields, oxygen/biomass ratios, and specific conversion rates. Interestingly, in combination, some of the carbon sources were consumed simultaneously and some sequentially. With a previously developed protocol, a sequential chemostat cultivation experiment was performed on a feed mixture of the six substrates. We found that the uptake of glucose, xylose, and mannose could be described with a Michaelis-Menten-type kinetics; however, these carbon sources seem to be competing for the same transport systems, while the uptake of arabinose, galacturonic acid, and rhamnose appeared to be repressed by the presence of other substrates.

  10. A stochastic model of enzyme kinetics

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    Stefanini, Marianne; Newman, Timothy; McKane, Alan

    2003-10-01

    Enzyme kinetics is generally modeled by deterministic rate equations, and in the simplest case leads to the well-known Michaelis-Menten equation. It is plausible that stochastic effects will play an important role at low enzyme concentrations. We have addressed this by constructing a simple stochastic model which can be exactly solved in the steady-state. Throughout a wide range of parameter values Michaelis-Menten dynamics is replaced by a new and simple theoretical result.

  11. Microscale Measurements of Michaelis-Menten Constants of Neuraminidase with Nanogel Capillary Electrophoresis for the Determination of the Sialic Acid Linkage.

    Science.gov (United States)

    Gattu, Srikanth; Crihfield, Cassandra L; Holland, Lisa A

    2017-01-03

    Phospholipid nanogels enhance the stability and performance of the exoglycosidase enzyme neuraminidase and are used to create a fixed zone of enzyme within a capillary. With nanogels, there is no need to covalently immobilize the enzyme, as it is physically constrained. This enables rapid quantification of Michaelis-Menten constants (K M ) for different substrates and ultimately provides a means to quantify the linkage (i.e., 2-3 versus 2-6) of sialic acids. The fixed zone of enzyme is inexpensive and easily positioned in the capillary to support electrophoresis mediated microanalysis using neuraminidase to analyze sialic acid linkages. To circumvent the limitations of diffusion during static incubation, the incubation period is reproducibly achieved by varying the number of forward and reverse passes the substrate makes through the stationary fixed zone using in-capillary electrophoretic mixing. A K M value of 3.3 ± 0.8 mM (V max , 2100 ± 200 μM/min) was obtained for 3'-sialyllactose labeled with 2-aminobenzoic acid using neuraminidase from Clostridium perfringens that cleaves sialic acid monomers with an α2-3,6,8,9 linkage, which is similar to values reported in the literature that required benchtop analyses. The enzyme cleaves the 2-3 linkage faster than the 2-6, and a K M of 2 ± 1 mM (V max , 400 ± 100 μM/min) was obtained for the 6'-sialyllactose substrate. An alternative neuraminidase selective for 2-3 sialic acid linkages generated a K M value of 3 ± 2 mM (V max , 900 ± 300 μM/min) for 3'-sialyllactose. With a knowledge of V max , the method was applied to a mixture of 2-3 and 2-6 sialyllactose as well as 2-3 and 2-6 sialylated triantennary glycan. Nanogel electrophoresis is an inexpensive, rapid, and simple alternative to current technologies used to distinguish the composition of 3' and 6' sialic acid linkages.

  12. Study on kinetics of glucose uptake by some species of plankton

    Science.gov (United States)

    Li, Wenquan; Wang, Xian; Zhang, Yaohua

    1993-03-01

    The rates of glucose uptake by some species of plankton were determined by3H-glucose tracer method. Experimental results indicated that the observed glucose uptake at natural seawater concentrations by Platymonas subcordiformis and Brachionus plicatilis was principally a metabolic process fitted with the Michaelis-Menten equation in the range of adaptive temperatures. Heterotrophic uptake by Platymonas subcordiformis was mainly dependent on diffusion at high glucose levels. The uptake by Brachionus plicatilis showed active transport even at high glucose levels, indicating its high heterotrophic activity. The uptake rate by Artemia salina was lower, and its V m/K ratio was lower than those of the other two species of plankton.

  13. Quantifying stream nutrient uptake from ambient to saturation with instantaneous tracer additions

    Science.gov (United States)

    Covino, T. P.; McGlynn, B. L.; McNamara, R.

    2009-12-01

    Stream nutrient tracer additions and spiraling metrics are frequently used to quantify stream ecosystem behavior. However, standard approaches limit our understanding of aquatic biogeochemistry. Specifically, the relationship between in-stream nutrient concentration and stream nutrient spiraling has not been characterized. The standard constant rate (steady-state) approach to stream spiraling parameter estimation, either through elevating nutrient concentration or adding isotopically labeled tracers (e.g. 15N), provides little information regarding the stream kinetic curve that represents the uptake-concentration relationship analogous to the Michaelis-Menten curve. These standard approaches provide single or a few data points and often focus on estimating ambient uptake under the conditions at the time of the experiment. Here we outline and demonstrate a new method using instantaneous nutrient additions and dynamic analyses of breakthrough curve (BTC) data to characterize the full relationship between spiraling metrics and nutrient concentration. We compare the results from these dynamic analyses to BTC-integrated, and standard steady-state approaches. Our results indicate good agreement between these three approaches but we highlight the advantages of our dynamic method. Specifically, our new dynamic method provides a cost-effective and efficient approach to: 1) characterize full concentration-spiraling metric curves; 2) estimate ambient spiraling metrics; 3) estimate Michaelis-Menten parameters maximum uptake (Umax) and the half-saturation constant (Km) from developed uptake-concentration kinetic curves, and; 4) measure dynamic nutrient spiraling in larger rivers where steady-state approaches are impractical.

  14. Kinetics of the norepinephrine analog [76Br]-meta-bromobenzylguanidine in isolated working rat heart

    International Nuclear Information System (INIS)

    Raffel, David; Loc'h, Christian; Mardon, Karine; Maziere, Bernard; Syrota, Andre

    1998-01-01

    A related set of kinetic studies of the norepinephrine analog [ 76 Br]-meta-bromobenzylguanidine (MBBG) were performed with an isolated working rat heart preparation. A series of constant infusion studies over a wide range of MBBG concentrations allowed estimation of the Michaelis-Menten constants for transport by the neuronal norepinephrine transporter (uptake 1 ) and the extraneuronal uptake system (uptake 2 ). Pharmacological blocking studies with inhibitors of uptake 1 , uptake 2 and vesicular uptake were performed to delineate the relative importance of these norepinephrine handling mechanisms on the kinetics of MBBG in the rat heart. Bolus injection studies were done to assess the ability of compartmental modeling techniques to characterize the kinetics of MBBG. These studies demonstrate that MBBG shares many of the same uptake mechanisms as norepinephrine in the rat heart. PET imaging studies with MBBG would be useful for assessing sympathetic nerve status in the living human heart

  15. Transient competitive complexation in biological kinetic isotope fractionation explains nonsteady isotopic effects: Theory and application to denitrification in soils

    Science.gov (United States)

    Maggi, Federico; Riley, William J.

    2009-12-01

    The theoretical formulation of biological kinetic isotope fractionation often assumes first-order or Michaelis-Menten kinetics, the latter solved under the quasi-steady state assumption. Both formulations lead to a constant isotope fractionation factor, therefore they may return incorrect estimations of isotopic effects and misleading interpretations of isotopic signatures when fractionation is not a steady process. We have analyzed the isotopic signature of denitrification in biogeochemical soil systems by Menyailo and Hungate (2006) in which high and variable 15N-N2O enrichment during N2O production and inverse isotope fractionation during N2O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with Michaelis-Menten kinetics. When Michaelis-Menten kinetics were coupled to Monod kinetics to describe biomass and enzyme dynamics, and the quasi-steady state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observed concentrations, and variable and inverse isotope fractionations. These results imply a substantial revision in modeling isotopic effects, suggesting that steady state kinetics such as first-order, Rayleigh, and classic Michaelis-Menten kinetics should be superseded by transient kinetics in conjunction with biomass and enzyme dynamics.

  16. Evaluation of rate law approximations in bottom-up kinetic models of metabolism

    DEFF Research Database (Denmark)

    Du, Bin; Zielinski, Daniel C.; Kavvas, Erol S.

    2016-01-01

    mass action rate law that removes the role of the enzyme from the reaction kinetics. We utilized in vivo data for the human red blood cell to compare the effect of rate law choices against the backdrop of physiological flux and concentration differences. We found that the Michaelis-Menten rate law......Background: The mechanistic description of enzyme kinetics in a dynamic model of metabolism requires specifying the numerical values of a large number of kinetic parameters. The parameterization challenge is often addressed through the use of simplifying approximations to form reaction rate laws....... These approximate rate laws were: 1) a Michaelis-Menten rate law with measured enzyme parameters, 2) a Michaelis-Menten rate law with approximated parameters, using the convenience kinetics convention, 3) a thermodynamic rate law resulting from a metabolite saturation assumption, and 4) a pure chemical reaction...

  17. Kinetics of adsorption and uptake of Cu2+ by Chlorella vulgaris: influence of pH, temperature, culture age, and cations.

    Science.gov (United States)

    Mehta, S K; Singh, Alpana; Gaur, J P

    2002-03-01

    Adsorption and uptake of Cu2+ by Chlorella vulgaris were distinguished by extracting the surface-bound Cu2+ with EDTA. The uptake of Cu2+ followed Michaelis Menten kinetics. The maximum rate of Cu2+ uptake (0.362fmolcell(-1) h(-1)) was obtained at pH 6.0. The rate of Cu2+ uptake was greater for cultures in the exponential phase of growth, and increased with a rise in temperature from 6 to 25 degrees C, thus pointing towards an active mechanism. The maximum number of Cu2+ binding sites was 3.245 fmol cell(-1) at pH 4.5. Adsorption of Cu2+ was strongly pH-dependent thereby indicating that the number and nature of metal binding sites on the cell surface change with changing chemistry of the solution. Unlike uptake, the adsorption remained unaffected by small changes in temperature. Older cultures displayed a higher Cu2+ adsorption capacity than the exponentially growing ones thus suggesting generation of new and/or additional Cu2+ binding sites on older cells of C. vulgaris. By pH titration, the cation-exchange capacity of Chlorella, measured in terms of H+/ Na+ exchange, was about 17 fmol cell(-1) at pH 10.5. Negligible cation exchange capacity at and below pH 5.0 indicated that ion exchange was not the sole mechanism of Cu2+ adsorption by Chlorella. The uptake and adsorption of Cu2+ were inhibited by 100 microM of various cations including other heavy metal ions. The general concept that cations competitively inhibit accumulation of metals in living organisms does not hold for C. vulgaris. Non-competitive, uncompetitive and mixed inhibition of Cu2+ uptake and adsorption by various cations were more common than competitive inhibition.

  18. Kinetics and mechanism of oxidation of aliphatic alcohols by ...

    Indian Academy of Sciences (India)

    TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the ...

  19. Nutrient Removal from Wastewater using Microalgae: A Kinetic Evaluation and Lipid Analysis.

    Science.gov (United States)

    2017-09-15

    The objective of this study was to examine the performance of mixed microalgal bioreactors in treating three differenttypes of wastewaters - kitchen wastewater (KWW), palm oil mill effluent (POME), and pharmaceutical wastewater (PWW) in semi-continuous mode and to analyze the lipid content in the harvested algal biomass. The reactors were monitored for total nitrogen and phosphate removal at eight solid retention times (SRTs) - 2, 4, 6, 8, 10, 12, 14, and 16 days. The nutrient uptake kinetic parameters were quantified using linearized Michaelis-Menten and Monod models at steady-state conditions. The nutrient removal efficiency and lipid production were found to be higher in KWW when compared with the other wastewaters. Saturated fatty acids (C16:0, C18:0, and C18:1) accounted for more than 60% of the algal fatty acids for all the wastewaters. The lipid is, therefore, considered suitable for synthesizing biodiesel.

  20. Electrophysiological approach to determine kinetic parameters of sucrose uptake by single sieve elements or phloem parenchyma cells in intact Vicia faba plants.

    Science.gov (United States)

    Hafke, Jens B; Höll, Sabina-Roxana; Kühn, Christina; van Bel, Aart J E

    2013-01-01

    Apart from cut aphid stylets in combination with electrophysiology, no attempts have been made thus far to measure in vivo sucrose-uptake properties of sieve elements. We investigated the kinetics of sucrose uptake by single sieve elements and phloem parenchyma cells in Vicia faba plants. To this end, microelectrodes were inserted into free-lying phloem cells in the main vein of the youngest fully-expanded leaf, half-way along the stem, in the transition zone between the autotrophic and heterotrophic part of the stem, and in the root axis. A top-to-bottom membrane potential gradient of sieve elements was observed along the stem (-130 mV to -110 mV), while the membrane potential of the phloem parenchyma cells was stable (approx. -100 mV). In roots, the membrane potential of sieve elements dropped abruptly to -55 mV. Bathing solutions having various sucrose concentrations were administered and sucrose/H(+)-induced depolarizations were recorded. Data analysis by non-linear least-square data fittings as well as by linear Eadie-Hofstee (EH) -transformations pointed at biphasic Michaelis-Menten kinetics (2 MM, EH: K m1 1.2-1.8 mM, K m2 6.6-9.0 mM) of sucrose uptake by sieve elements. However, Akaike's Information Criterion (AIC) favored single MM kinetics. Using single MM as the best-fitting model, K m values for sucrose uptake by sieve elements decreased along the plant axis from 1 to 7 mM. For phloem parenchyma cells, higher K m values (EH: K m1 10 mM, K m2 70 mM) as compared to sieve elements were found. In preliminary patch-clamp experiments with sieve-element protoplasts, small sucrose-coupled proton currents (-0.1 to -0.3 pA/pF) were detected in the whole-cell mode. In conclusion (a) K m values for sucrose uptake measured by electrophysiology are similar to those obtained with heterologous systems, (b) electrophysiology provides a useful tool for in situ determination of K m values, (c) As yet, it remains unclear if one or two uptake systems are involved in sucrose

  1. Transient competitive complexation in biological kinetic isotope fractionation explains non-steady isotopic effects: Theory and application to denitrification in soils

    Energy Technology Data Exchange (ETDEWEB)

    Maggi, F.M.; Riley, W.J.

    2009-06-01

    The theoretical formulation of biological kinetic reactions in isotopic applications often assume first-order or Michaelis-Menten-Monod kinetics under the quasi-steady-state assumption to simplify the system kinetics. However, isotopic e ects have the same order of magnitude as the potential error introduced by these simpli cations. Both formulations lead to a constant fractionation factor which may yield incorrect estimations of the isotopic effect and a misleading interpretation of the isotopic signature of a reaction. We have analyzed the isotopic signature of denitri cation in biogeochemical soil systems by Menyailo and Hungate [2006], where high {sup 15}N{sub 2}O enrichment during N{sub 2}O production and inverse isotope fractionation during N{sub 2}O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with the quasi-steady-state Michaelis-Menten-Monod kinetics. When the quasi-steady-state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation of isotopic signatures and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi-steady-state Michaelis-Menten-Monod kinetics.

  2. Comparison of dopamine kinetics in the larval Drosophila ventral nerve cord and protocerebrum with improved optogenetic stimulation.

    Science.gov (United States)

    Privman, Eve; Venton, B Jill

    2015-11-01

    Dopamine release and uptake have been studied in the Drosophila larval ventral nerve cord (VNC) using optogenetics to stimulate endogenous release. However, other areas of the central nervous system remain uncharacterized. Here, we compare dopamine release in the VNC and protocerebrum of larval Drosophila. Stimulations were performed with CsChrimson, a new, improved, red light-activated channelrhodopsin. In both regions, dopamine release was observed after only a single, 4 ms duration light pulse. Michaelis-Menten modeling was used to understand release and uptake parameters for dopamine. The amount of dopamine released ([DA]p ) on the first stimulation pulse is higher than the average [DA]p released from subsequent pulses. The initial and average amount of dopamine released per stimulation pulse is smaller in the protocerebrum than in the VNC. The average Vmax of 0.08 μM/s in the protocerebrum was significantly higher than the Vmax of 0.05 μM/s in the VNC. The average Km of 0.11 μM in the protocerebrum was not significantly different from the Km of 0.10 μM in the VNC. When the competitive dopamine transporter (DAT) inhibitor nisoxetine was applied, the Km increased significantly in both regions while Vmax stayed the same. This work demonstrates regional differences in dopamine release and uptake kinetics, indicating important variation in the amount of dopamine available for neurotransmission and neuromodulation. We use a new optogenetic tool, red light activated CsChrimson, to stimulate the release of dopamine in the ventral nerve cord and medial protocerebrum of the larval Drosophila central nervous system. We monitored extracellular dopamine by fast scan cyclic voltammetry and used Michaelis-Menten modeling to probe the regulation of extracellular dopamine, discovering important similarities and differences in these two regions. © 2015 International Society for Neurochemistry.

  3. Phosphorus Uptake Kinetics of Different Types of Duckweed.%不同品种浮萍磷素吸收动力学特征

    Institute of Scientific and Technical Information of China (English)

    蔡树美; 刘文桃; 张震; 柏彦超; 钱晓晴

    2011-01-01

    以长江三角洲地区常见的3种浮萍--稀脉浮萍(Lemna aequinoctialis)、少根紫萍(Spirodela oligorrhiza)和紫萍(Spriodela polyrrhiza)为对象,研究不同品种浮萍对HPO42-的吸收动力学影响.结果表明,3种浮萍对无机磷的吸收动力学特征基本可采用Michaelis-Menten方程描述,3种浮萍无机磷吸收速率V对磷浓度S双倒数曲线的拟合关系均在α=0.01水平上显著.稀脉浮萍对无机磷的亲和力较强,适宜应用于对低磷浓度污水的净化;紫萍对无机磷的最大吸收速率Vmax较高,适宜应用于对高磷浓度污水的净化.%An increasing attention has been paid to the use of duckweed in treating eutrophicated water as a tool of bio-remediation of domestic wastewater.Phosphorus uptake kinetics was studied,of different species of duckweeds, i.e.Lemna aequinoctialis, Spirodela oligorrhiza and Spriodela polyrrhiza, which are common in the Yangtze River Delta area.Results show that the phosphorus uptake kinetics of the duckweeds could be expressed with the Michaelis-Menten equation; and the relation between phosphorus uptake rate (V) of the duckweeds and inorganic phosphorus(Pi) concentration (S), was well fitted with a double-reciprocal curve with at =0.01; the Km value for Pi uptake of Lemna aequinoctialis was lower than that of Spirodela oligorrhiza and Spriodela polyrrhiza, making it a better candidate for treating wastewater low in Pi concentration.The maximum phosphorus uptake rate of Spriodela polyrrhiza was higher than that of the other two species, which allows Spriodela polyrrhiza better performance in purifying wastewater higher in Pi concentration.

  4. Thermodynamic Activity-Based Progress Curve Analysis in Enzyme Kinetics.

    Science.gov (United States)

    Pleiss, Jürgen

    2018-03-01

    Macrokinetic Michaelis-Menten models based on thermodynamic activity provide insights into enzyme kinetics because they separate substrate-enzyme from substrate-solvent interactions. Kinetic parameters are estimated from experimental progress curves of enzyme-catalyzed reactions. Three pitfalls are discussed: deviations between thermodynamic and concentration-based models, product effects on the substrate activity coefficient, and product inhibition. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Uptake of oxytetracycline and its phytotoxicity to alfalfa (Medicago sativa L.)

    Energy Technology Data Exchange (ETDEWEB)

    Kong, W D [Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China); Zhu, Y G [Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China); Liang, Y C [Ministry of Agriculture Key Laboratory of Plant Nutrition and Nutrient Cycling, Institute of Soils and Fertilizers, Chinese Academy of Agricultural Sciences, Beijing 100081 (China); Zhang, J [Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China); Smith, F A [Soil and Land Systems, School of Earth and Environmental Sciences, University of Adelaide, DP 636, Adelaide, SA 5005 (Australia); Yang, M [Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China)

    2007-05-15

    A series of experiments were conducted in a hydroponic system to investigate the uptake of oxytetracycline (OTC) and its toxicity to alfalfa (Medicago sativa L.). OTC inhibited alfalfa shoot and root growth by up to 61% and 85%, respectively. The kinetics of OTC uptake could be well described by Michaelis-Menten equation with V {sub max} of 2.25 {mu}mol g{sup -1} fresh weight h{sup -1}, and K {sub m} of 0.036 mM. The uptake of OTC by alfalfa was strongly inhibited by the metabolic inhibitor, 2,4-DNP (2,4-dinitrophenol), at pH 3.5 and 6.0, but not by the aquaporin competitors, glycerol and Ag{sup +}. OTC uptake, however, was significantly inhibited by Hg{sup 2+}, suggesting that the inhibition of influx was due to general cellular stress rather than the specific action of Hg{sup 2+} on aquaporins. Results from the present study suggested that OTC uptake into alfalfa is an energy-dependent process. - Plant uptake of antibiotic oxytetracycline is energy-dependent.

  6. Uptake of oxytetracycline and its phytotoxicity to alfalfa (Medicago sativa L.)

    International Nuclear Information System (INIS)

    Kong, W.D.; Zhu, Y.G.; Liang, Y.C.; Zhang, J.; Smith, F.A.; Yang, M.

    2007-01-01

    A series of experiments were conducted in a hydroponic system to investigate the uptake of oxytetracycline (OTC) and its toxicity to alfalfa (Medicago sativa L.). OTC inhibited alfalfa shoot and root growth by up to 61% and 85%, respectively. The kinetics of OTC uptake could be well described by Michaelis-Menten equation with V max of 2.25 μmol g -1 fresh weight h -1 , and K m of 0.036 mM. The uptake of OTC by alfalfa was strongly inhibited by the metabolic inhibitor, 2,4-DNP (2,4-dinitrophenol), at pH 3.5 and 6.0, but not by the aquaporin competitors, glycerol and Ag + . OTC uptake, however, was significantly inhibited by Hg 2+ , suggesting that the inhibition of influx was due to general cellular stress rather than the specific action of Hg 2+ on aquaporins. Results from the present study suggested that OTC uptake into alfalfa is an energy-dependent process. - Plant uptake of antibiotic oxytetracycline is energy-dependent

  7. Subcellular distribution and uptake mechanism of di-n-butyl phthalate in roots of pumpkin (Cucurbita moschata) seedlings.

    Science.gov (United States)

    Lin, Qingqi; Yang, Xiuhong; Huang, Xiongfei; Wang, Shizhong; Chao, Yuanqing; Qiu, Rongliang

    2016-01-01

    Phthalate acid esters (PAEs) are of particular concern due to their potential environmental risk to human and nonhuman organisms. Although uptake of PAEs by plants has been reported by several researchers, information about the intracellular distribution and uptake mechanisms of PAEs is still lacking. In this study, a series of hydroponic experiments using intact pumpkin (Cucurbita moschata) seedlings was conducted to investigate how di-n-butyl phthalate (DnBP), one of the most frequently identified PAEs in the environment, enters and is distributed in roots. DnBP was transported into subcellular tissues rapidly in the initial uptake period (<12 h). More than 80% of DnBP was detected in the cell walls and organelles, which suggests that DnBP is primarily accumulated in these two fractions due to their high affinity to DnBP. The kinetics of DnBP uptake were fitted well with the Michaelis-Menten equation, suggesting that a carrier-mediated process was involved. The application of 2,4-dinitrophenol and sodium vanadate reduced the uptake of DnBP by 37 and 26%, respectively, while aquaporin inhibitors, silver and glycerol, had no effect on DnBP uptake. These data demonstrated that the uptake of DnBP included a carrier-mediated and energy-dependent process without the participation of aquaporins.

  8. Uptake of acidic and basic sugar derivatives in Lemna gibba G1

    International Nuclear Information System (INIS)

    Sanz, A.; Ullrich, C.I.

    1989-01-01

    The uptake of acidic and basic sugar derivatives in Lemna gibba L. was studied. Uronic acids applied to the experimental solution induced a small decrease of the membrane potential. After incubation of the plants in a 0.1 millimolar solution of these substrates, no decrease in the concentration of reducing groups in the external solution was detected. Respiration increased by 31% with 50 millimolar galacturonic acid, whereas no effect was found with the same concentration of glucuronic acid. Glucosamine caused a considerable concentration-dependent membrane depolarization. ( 14 C)glucosamine uptake followed Michaelis-Menten kinetics together with a linear component. Influx of this substrate was inhibited by glucose but the type of competition could not be clearly distinguished. Glucosamine, 50 millimolar, inhibited the respiration rate by 30%. The glucosamine uptake was pH-dependent, with maximum uptake at around pH 7. Lack of enhancement of uptake by low pH as well as the permanent membrane depolarization suggest a uniport mechanism for the charged species of the substrate and an electroneutral diffusion of the uncharged species

  9. Kinetics of Butyrate, Acetate, and Hydrogen Metabolism in a Thermophilic, Anaerobic, Butyrate-Degrading Triculture

    OpenAIRE

    Ahring, Birgitte K.; Westermann, Peter

    1987-01-01

    Kinetics of butyrate, acetate, and hydrogen metabolism were determined with butyrate-limited, chemostat-grown tricultures of a thermophilic butyrate-utilizing bacterium together with Methanobacterium thermoautotrophicum and the TAM organism, a thermophilic acetate-utilizing methanogenic rod. Kinetic parameters were determined from progress curves fitted to the integrated form of the Michaelis-Menten equation. The apparent half-saturation constants, Km, for butyrate, acetate, and dissolved hyd...

  10. New types of experimental data shape the use of enzyme kinetics for dynamic network modeling.

    Science.gov (United States)

    Tummler, Katja; Lubitz, Timo; Schelker, Max; Klipp, Edda

    2014-01-01

    Since the publication of Leonor Michaelis and Maude Menten's paper on the reaction kinetics of the enzyme invertase in 1913, molecular biology has evolved tremendously. New measurement techniques allow in vivo characterization of the whole genome, proteome or transcriptome of cells, whereas the classical enzyme essay only allows determination of the two Michaelis-Menten parameters V and K(m). Nevertheless, Michaelis-Menten kinetics are still commonly used, not only in the in vitro context of enzyme characterization but also as a rate law for enzymatic reactions in larger biochemical reaction networks. In this review, we give an overview of the historical development of kinetic rate laws originating from Michaelis-Menten kinetics over the past 100 years. Furthermore, we briefly summarize the experimental techniques used for the characterization of enzymes, and discuss web resources that systematically store kinetic parameters and related information. Finally, describe the novel opportunities that arise from using these data in dynamic mathematical modeling. In this framework, traditional in vitro approaches may be combined with modern genome-scale measurements to foster thorough understanding of the underlying complex mechanisms. © 2013 FEBS.

  11. Semi-Mechanistic Population Pharmacokinetic Modeling of L-Histidine Disposition and Brain Uptake in Wildtype and Pht1 Null Mice.

    Science.gov (United States)

    Wang, Xiao-Xing; Li, Yang-Bing; Feng, Meihua R; Smith, David E

    2018-01-05

    To develop a semi-mechanistic population pharmacokinetic (PK) model to quantitate the disposition kinetics of L-histidine, a peptide-histidine transporter 1 (PHT1) substrate, in the plasma, cerebrospinal fluid and brain parenchyma of wildtype (WT) and Pht1 knockout (KO) mice. L-[ 14 C]Hisidine (L-His) was administrated to WT and KO mice via tail vein injection, after which plasma, cerebrospinal fluid (CSF) and brain parenchyma samples were collected. A PK model was developed using non-linear mixed effects modeling (NONMEM). The disposition of L-His between the plasma, brain, and CSF was described by a combination of PHT1-mediated uptake, CSF bulk flow and first-order micro-rate constants. The PK profile of L-His was best described by a four-compartment model. A more rapid uptake of L-His in brain parenchyma was observed in WT mice due to PHT1-mediated uptake, a process characterized by a Michaelis-Menten component (V max  = 0.051 nmoL/min and K m  = 34.94 μM). A semi-mechanistic population PK model was successfully developed, for the first time, to quantitatively characterize the disposition kinetics of L-His in brain under in vivo conditions. This model may prove a useful tool in predicting the uptake of L-His, and possibly other PHT1 peptide/mimetic substrates, for drug delivery to the brain.

  12. Study on biofiltration capacity and kinetics of nutrient uptake by Gracilaria cervicornis (Turner J. Agardh (Rhodophyta, Gracilariaceae

    Directory of Open Access Journals (Sweden)

    Marcella A. A. Carneiro

    2011-04-01

    Full Text Available The absorption efficiency and kinetic parameters (Vmax, Ks and Vmax:Ks of the seaweed Gracilaria cervicornis for the nutrients NH4+, NO3- and PO4(3- were evaluated. Absorption efficiency was measured by monitoring nutrient concentrations for 5 h in culture media with initial concentrations of 5, 10, 20 and 30µM. Kinetic parameters were determined by using the Michaelis-Menten formula. Absorption efficiencies for this algae were greater in treatments with lower concentrations, as evidenced by a reduction of 85.3, 97.5 and 81.2% for NH4+, NO3- and PO4(3-, respectively. Kinetic parameters show that G. cervicornis exhibits greater ability to take up high concentrations of NH4+ (Vmax=158.5µM g dw-1 h-1 and low concentrations of PO4(3- (Ks=5µM and Vmax:Ks=10.3. These results suggest that this algal species has good absorption capacity for the nutrients tested and may be a promising candidate as a bioremediator of eutrophized environments.

  13. Uptake, accumulation and metabolic response of ferricyanide in weeping willows.

    Science.gov (United States)

    Yu, Xiao-Zhang; Gu, Ji-Dong

    2009-01-01

    The remediation potential and metabolic responses of plants to ferricyanide were investigated using pre-rooted weeping willows (Salix babylonica L.) grown hydroponically in growth chambers and treated with potassium ferricyanide. Positive responses were observed for the plants exposed to cyanide recovered in plant biomass was constant in all treatments, indicating that transport is a major limiting step for the uptake of ferricyanide by plants. The majority of the ferricyanide taken up from the growth media was possibly assimilated during transport through plants. The velocity of the removal processes can be described by Michaelis-Menten kinetics, and the half-saturation constant (K(M)) and the maximum removal capacity (v(max)) were estimated to be 228.1 mg CN L(-1) and 36.43 mg CN kg(-1) d(-1), respectively, using non-linear regression methods. These results suggest that weeping willows can take up, transport and assimilate ferricyanide; and phytoremediation is an option for cleaning up the environmental sites contaminated with cyanide complexes.

  14. Kinetics of butyrate, acetate, and hydrogen metabolism in a thermophilic, anaerobic, butyrate-degrading triculture.

    Science.gov (United States)

    Ahring, B K; Westermann, P

    1987-02-01

    Kinetics of butyrate, acetate, and hydrogen metabolism were determined with butyrate-limited, chemostat-grown tricultures of a thermophilic butyrate-utilizing bacterium together with Methanobacterium thermoautotrophicum and the TAM organism, a thermophilic acetate-utilizing methanogenic rod. Kinetic parameters were determined from progress curves fitted to the integrated form of the Michaelis-Menten equation. The apparent half-saturation constants, K(m), for butyrate, acetate, and dissolved hydrogen were 76 muM, 0.4 mM, and 8.5 muM, respectively. Butyrate and hydrogen were metabolized to a concentration of less than 1 muM, whereas acetate uptake usually ceased at a concentration of 25 to 75 muM, indicating a threshold level for acetate uptake. No significant differences in K(m) values for butyrate degradation were found between chemostat- and batch-grown tricultures, although the maximum growth rate was somewhat higher in the batch cultures in which the medium was supplemented with yeast extract. Acetate utilization was found to be the rate-limiting reaction for complete degradation of butyrate to methane and carbon dioxide in continuous culture. Increasing the dilution rate resulted in a gradual accumulation of acetate. The results explain the low concentrations of butyrate and hydrogen normally found during anaerobic digestion and the observation that acetate is the first volatile fatty acid to accumulate upon a decrease in retention time or increase in organic loading of a digestor.

  15. Taurine uptake by human retinal pigment epithelium: implications for the transport of small solutes between the choroid and the outer retina.

    Science.gov (United States)

    Hillenkamp, Jost; Hussain, Ali A; Jackson, Timothy L; Cunningham, Joanna R; Marshall, John

    2004-12-01

    To characterize the Michaelis-Menten kinetics of the taurine transporter (TT) in retinal pigment epithelium (RPE) freshly isolated from human donor eyes. To identify the rate limiting compartment in the pathway of taurine delivery from the choroidal blood supply to the outer retina composed by Bruch's-choroid (BC) and the RPE in the human older age group. In human donor samples (4 melanoma-affected eyes, and 14 control eyes; age range, 62-93 years), radiochemical techniques were used to determine the RPE taurine accumulation at various exogenous concentrations. The transport capability of human RPE was obtained from a kinetic analysis of the high-affinity carrier over a substrate concentration of 1 to 60 microM taurine. Uptake of taurine into human RPE at a taurine concentration of 1 microM was independent of donor age (P > 0.05) and averaged at 2.83 +/- 0.27 (SEM) pmol/10 minutes per 6-mm trephine. Taurine transport by human RPE was mediated by a high-affinity carrier of K(m) 50 microM and V(max) of 267 pmol/10 minutes per 5-mm disc. In human donor RPE, uptake of taurine remained viable in the age range 62 to 93 years. Taurine transport rates in the RPE were lower than across the isolated BC complex, and thus the data suggest that the former compartment houses the rate-limiting step in the delivery of taurine to the outer retina.

  16. Muscular Oxygen Uptake Kinetics in Aged Adults.

    Science.gov (United States)

    Koschate, J; Drescher, U; Baum, K; Eichberg, S; Schiffer, T; Latsch, J; Brixius, K; Hoffmann, U

    2016-06-01

    Pulmonary oxygen uptake (V˙O2) kinetics and heart rate kinetics are influenced by age and fitness. Muscular V˙O2 kinetics can be estimated from heart rate and pulmonary V˙O2. In this study the applicability of a test using pseudo-random binary sequences in combination with a model to estimate muscular V˙O2 kinetics was tested. Muscular V˙O2 kinetics were expected to be faster than pulmonary V˙O2 kinetics, slowed in aged subjects and correlated with maximum V˙O2 and heart rate kinetics. 27 elderly subjects (73±3 years; 81.1±8.2 kg; 175±4.7 cm) participated. Cardiorespiratory kinetics were assessed using the maximum of cross-correlation functions, higher maxima implying faster kinetics. Muscular V˙O2 kinetics were faster than pulmonary V˙O2 kinetics (0.31±0.1 vs. 0.29±0.1 s; p=0.004). Heart rate kinetics were not correlated with muscular or pulmonary V˙O2 kinetics or maximum V˙O2. Muscular V˙O2 kinetics correlated with maximum V˙O2 (r=0.35; p=0.033). This suggests, that muscular V˙O2 kinetics are faster than estimates from pulmonary V˙O2 and related to maximum V˙O2 in aged subjects. In the future this experimental approach may help to characterize alterations in muscular V˙O2 under various conditions independent of motivation and maximal effort. © Georg Thieme Verlag KG Stuttgart · New York.

  17. The steady-state kinetics of the NADH-dependent nitrite reductase from Escherichia coli K 12. Nitrite and hydroxylamine reduction.

    OpenAIRE

    Jackson, R H; Cole, J A; Cornish-Bowden, A

    1981-01-01

    The reduction of both NO2- and hydroxylamine by the NADH-dependent nitrite reductase of Escherichia coli K 12 (EC 1.6.6.4) appears to follow Michaelis-Menten kinetics over a wide range of NADH concentrations. Substrate inhibition can, however, be detected at low concentrations of the product NAD+. In addition, NAD+ displays mixed product inhibition with respect to NADH and mixed or uncompetitive inhibition with respect to hydroxylamine. These inhibition characteristics are consistent with a m...

  18. Fatty acid uptake in normal human myocardium

    International Nuclear Information System (INIS)

    Vyska, K.; Meyer, W.; Stremmel, W.; Notohamiprodjo, G.; Minami, K.; Machulla, H.J.; Gleichmann, U.; Meyer, H.; Koerfer, R.

    1991-01-01

    Fatty acid binding protein has been found in rat aortic endothelial cell membrane. It has been identified to be a 40-kDa protein that corresponds to a 40-kDa fatty acid binding protein with high affinity for a variety of long chain fatty acids isolated from rat heart myocytes. It is proposed that this endothelial membrane fatty acid binding protein might mediate the myocardial uptake of fatty acids. For evaluation of this hypothesis in vivo, influx kinetics of tracer-labeled fatty acids was examined in 15 normal subjects by scintigraphic techniques. Variation of the plasma fatty acid concentration and plasma perfusion rate has been achieved by modulation of nutrition state and exercise conditions. The clinical results suggest that the myocardial fatty acid influx rate is saturable by increasing fatty acid plasma concentration as well as by increasing plasma flow. For analysis of these data, functional relations describing fatty acid transport from plasma into myocardial tissue in the presence and absence of an unstirred layer were developed. The fitting of these relations to experimental data indicate that the free fatty acid influx into myocardial tissue reveals the criteria of a reaction on a capillary surface in the vicinity of flowing plasma but not of a reaction in extravascular space or in an unstirred layer and that the fatty acid influx into normal myocardium is a saturable process that is characterized by the quantity corresponding to the Michaelis-Menten constant, Km, and the maximal velocity, Vmax, 0.24 ± 0.024 mumol/g and 0.37 ± 0.013 mumol/g(g.min), respectively. These data are compatible with a nondiffusional uptake process mediated by the initial interaction of fatty acids with the 40-kDa membrane fatty acid binding protein of cardiac endothelial cells

  19. A kinetic model for the penicillin biosynthetic pathway in

    DEFF Research Database (Denmark)

    Nielsen, Jens; Jørgensen, Henrik

    1996-01-01

    A kinetic model for the first two steps in the penicillin biosynthetic pathway, i.e. the ACV synthetase (ACVS) and the isopenicillin N synthetase (IPNS) is proposed. The model is based on Michaelis-Menten type kinetics with non-competitive inhibition of the ACVS by ACV, and competitive inhibition...... of the IPNS by glutathione. The model predicted flux through the pathway corresponds well with the measured rate of penicillin biosynthesis. From the kinetic model the elasticity coefficients and the flux control coefficients are calculated throughout a fed-batch cultivation, and it is found...

  20. Studies on the kinetics of absorption of phosphorus by rice (Orysa sativa L.) and beans (Phaseolus vulgaris L.)

    International Nuclear Information System (INIS)

    Baraibar, A.; Villamil, J.; Fiore, M.F.; Marcondes, R.F.; Muraoka, T.; Cabral, C.P.; Malavolta, M.L.; Malavolta, E.

    1987-01-01

    Three experiments were conducted under controlled conditions with the objectives of evaluating the effect of different concentrations of phosphorus and on the presence of other ions on the kinetic of absorption. Excised roots of rice and bean were placed in aereated solutions containing increasing concentrations of NaH 2 PO 4 (10 -7 M to 5x10 -2 M) during 90 minutes. The rate of absorption (v = umols P/g dry matter) and the kinetic constants Vmax and Km were determined. Similar procedure was used to to evaluate the interaction of Mg +2 , Al +3 , K + , N-NH 4 + , N-NO 3 - and N-ureia in the uptake of phosphorus during 120 minutes. In another experiment, the effect of the presence of Mg +2 and/for Al +3 in the uptake and redistribution of phosphorus, was evaluated by varying the external concentration (1 ppm, 5 ppm, 10 ppm and 20 ppm) during a period of 17 hours, and utilizing whole rice plants. It was observed a dual mechanism, with two phases following the Michaelis-Menten kinetics and with transition phase 1 - 50 x 10 -5 M. The best explanation of the experimental data was obtained, by transforming the data in accordance with HOFSTEE (1952). Bean was more efficient than rice in the first phase of uptake (higher Vmax). Al 3 had a clear stimulatory effect on the uptake of phosphorus, promoting, however, the anion fixation in the root at lower concentrations. At the highest concentrations (20 ppm) of phosphorus this effect was not evident. No effect on the uptake was observed with Mg +2 , K + and different forms of nitrogen. Urea could have a depressive effect although, not significant. Possible mechanisms involved are discussed. (author) [pt

  1. [Investigations on the physiology of the glands of carnivorous plants : IV. The kinetics of chloride secretion by the gland tissue of Nepenthes].

    Science.gov (United States)

    Lüttge, U

    1966-03-01

    The transport of chloride in isolated tissue from Nepenthes pitchers was investigated using (36)Cl(-), an Aminco-Cotlove chloride-titrator for the determinations of Cl(-) concentrations, and KCN and AsO 4 (-) -as metabolic inhibitors.The tissue was brought in contact with different experimental solutions (=medium). The surface corresponding to the outside of the pitchers was cut with a razor blade to remove the cutinized epidermal layer. At this surface the Cl(-) uptake from the medium is a metabolic process which depends on the Cl(-)-concentration of the medium in a manner that corresponds to the MICHAELIS-MENTEN kinetics. The Michaelis-constant of this transport step was 3×10(-2)M. The Cl(-)-efflux into the medium, however, is a passive process.The opposite surface of the tissue slices (corresponding to the inside of the pitchers) carries the glands. The chloride secretion taking place here is also dependent on metabolism. In vitro it occurs even when a high gradient of chloride concentration has been set up between the medium and the solution which is in contact with the glands. In vivo the Cl(-)-concentration of the pitcher fluid and the amount of Cl(-) per gram of tissue water are almost equal.The rôle of chloride in the physiology of Nepenthes is still under investigation, A correlation between the chloride content of the pitcher fluid and its enzymatic activity (Casein-test), however, could already be demonstrated.

  2. Decreased uptake of 3H-serotonin and endogenous content of serotonin in blood platelets in hypertensive patients

    International Nuclear Information System (INIS)

    Kamal, L.A.; Le Quan-Bui, K.H.; Meyer, P.

    1984-01-01

    The uptake and content of serotonin in blood platelets were studied in patients with essential hypertension and in five families in which at least one member was hypertensive. Blood was obtained from male and female normotensive volunteers and hypertensive patients who were free of medication. Lineweaver-Burk plots of 3H-serotonin uptake from both control subjects and hypertensive patients were linear, which suggested simple Michaelis-Menten uptake kinetics. The maximal uptake velocity (Vmax) in hypertensive patients was significantly lower than in control subjects (control . 41.7 +/- 3.3 pmol/min/10(8) platelets, n . 17; hypertensive . 26.6 +/- 3.0 pmol/min/10(8) platelets, n . 16; p less than 0.005). The affinity constant (Km) was slightly but significantly lower in hypertensive patients (control . 0.70 +/- 0.08 microM; hypertensive . 0.46 +/- 0.08 microM; p less than 0.05). The serotonin content in blood platelets determined by high pressure liquid chromatography with electrochemical detection was significantly lower in hypertensive patients (control . 165.0 +/- 12.9 nmol/10(11) platelets, n . 29; hypertensive . 105.9 +/- 10.4 nmol/10(11) platelets, n . 27; p less than 0.001). In the five families investigated, the lowered serotonin content was observed in some normotensive members. The reduced number of carriers of serotonin uptake and the slight decrease in the affinity constant observed in platelets of patients with essential hypertension suggest that serotonin metabolism is altered in essential hypertension and that blood platelets may be a useful model in studying the serotonergic modifications at the molecular level

  3. Uptake kinetics of arsenic by lettuce cultivars under hydroponics ...

    African Journals Online (AJOL)

    Arsenic (As) uptake ability based on kinetic parameters by two lettuce cultivars; Sijibaiye (SJBY) and Texuanyanlingsun (TXYLS) was investigated in nutrient solution containing eight levels of arsenic (As). Depletion of As from solution was monitored over a period of 24 h at regular time to estimate As uptake kinetics of the ...

  4. Solution of non-steady-state substrate concentration in the action of biosensor response at mixed enzyme kinetics

    Science.gov (United States)

    Senthamarai, R.; Jana Ranjani, R.

    2018-04-01

    In this paper, a mathematical model of an amperometric biosensor at mixed enzyme kinetics and diffusion limitation in the case of substrate inhibition has been developed. The model is based on time dependent reaction diffusion equation containing a non -linear term related to non -Michaelis - Menten kinetics of the enzymatic reaction. Solution for the concentration of the substrate has been derived for all values of parameters using the homotopy perturbation method. All the approximate analytic expressions of substrate concentration are compared with simulation results using Scilab/Matlab program. Finally, we have given a satisfactory agreement between them.

  5. Root uptake of uranium by a higher plant model (Phaseolus vulgaris) bioavailability from soil solution

    Energy Technology Data Exchange (ETDEWEB)

    Laroche, L.; Henner, P.; Camilleri, V.; Garnier-Laplace, J. [CEA Cadarache (DEI/SECRE/LRE), Laboratory of Radioecology and Ecotoxicology, Institute for Radioprotection and Nuclear Safety, 13 - Saint-Paul-lez-Durance (France)

    2004-07-01

    Uranium behaviour in soils is controlled by actions and interactions between physicochemical and biological processes that also determine its bioavailability. In soil solution, uranium(+VI) aqueous speciation undergoes tremendous changes mainly depending on pH, carbonates, phosphates and organic matter. In a first approach to identify bioavailable species of U to plants, cultures were performed using hydroponics, to allow an easy control of the composition of the exposure media. The latter, here an artificial soil solution, was designed to control the uranium species in solution. The geochemical speciation code JCHESS using a database compiled from the OECD/NEA thermochemical database project and verified was used to perform the solution speciation calculations. On this theoretical basis, three domains were defined for short-duration well-defined laboratory experiments in simplified conditions: pH 4.9, 5.8 and 7 where predicted dominant species are uranyl ions, hydroxyl complexes and carbonates respectively. For these domains, biokinetics and characterization of transmembrane transport according to a classical Michaelis Menten approach were investigated. The Free Ion Model (or its derived Biotic Ligand Model) was tested to determine if U uptake is governed by the free uranyl species or if other metal complexes can be assimilated. The effect of different variables on root assimilation efficiency and phyto-toxicity was explored: presence of ligands such as phosphates or carbonates and competitive ions such as Ca{sup 2+} at the 3 pH. According to previous experiments, uranium was principally located in roots whatever the pH and no difference in uranium uptake was evidenced between the main growth stages of the plant. Within the 3 studied chemical domains, results from short-term kinetics evidenced a linear correlation between total uranium concentration in bean roots and that in exposure media, suggesting that total uranium in soil solution could be a good predictor

  6. Root uptake of uranium by a higher plant model (Phaseolus vulgaris) bioavailability from soil solution

    International Nuclear Information System (INIS)

    Laroche, L.; Henner, P.; Camilleri, V.; Garnier-Laplace, J.

    2004-01-01

    Uranium behaviour in soils is controlled by actions and interactions between physicochemical and biological processes that also determine its bioavailability. In soil solution, uranium(+VI) aqueous speciation undergoes tremendous changes mainly depending on pH, carbonates, phosphates and organic matter. In a first approach to identify bioavailable species of U to plants, cultures were performed using hydroponics, to allow an easy control of the composition of the exposure media. The latter, here an artificial soil solution, was designed to control the uranium species in solution. The geochemical speciation code JCHESS using a database compiled from the OECD/NEA thermochemical database project and verified was used to perform the solution speciation calculations. On this theoretical basis, three domains were defined for short-duration well-defined laboratory experiments in simplified conditions: pH 4.9, 5.8 and 7 where predicted dominant species are uranyl ions, hydroxyl complexes and carbonates respectively. For these domains, biokinetics and characterization of transmembrane transport according to a classical Michaelis Menten approach were investigated. The Free Ion Model (or its derived Biotic Ligand Model) was tested to determine if U uptake is governed by the free uranyl species or if other metal complexes can be assimilated. The effect of different variables on root assimilation efficiency and phyto-toxicity was explored: presence of ligands such as phosphates or carbonates and competitive ions such as Ca 2+ at the 3 pH. According to previous experiments, uranium was principally located in roots whatever the pH and no difference in uranium uptake was evidenced between the main growth stages of the plant. Within the 3 studied chemical domains, results from short-term kinetics evidenced a linear correlation between total uranium concentration in bean roots and that in exposure media, suggesting that total uranium in soil solution could be a good predictor for

  7. Nitrogen uptake kinetics of freshly isolated zooxanthellae

    Digital Repository Service at National Institute of Oceanography (India)

    Wafar, M.V.M.; Wafar, S.; Rajkumar, R.

    that for nitrate [2.8 nmol. ( mu chl-a)./1h/1] and urea [0.37 nmol. ( mu chl-a)./1h/1]. Half-saturation constants for uptake of the three nitrogen compounds were in the range of 10-15 mu mol.l/1. Generally, uptake of any one nitrogen substrate appears to be inhibit...

  8. Emergence of dynamic cooperativity in the stochastic kinetics of fluctuating enzymes

    International Nuclear Information System (INIS)

    Kumar, Ashutosh; Chatterjee, Sambarta; Nandi, Mintu; Dua, Arti

    2016-01-01

    Dynamic co-operativity in monomeric enzymes is characterized in terms of a non-Michaelis-Menten kinetic behaviour. The latter is believed to be associated with mechanisms that include multiple reaction pathways due to enzymatic conformational fluctuations. Recent advances in single-molecule fluorescence spectroscopy have provided new fundamental insights on the possible mechanisms underlying reactions catalyzed by fluctuating enzymes. Here, we present a bottom-up approach to understand enzyme turnover kinetics at physiologically relevant mesoscopic concentrations informed by mechanisms extracted from single-molecule stochastic trajectories. The stochastic approach, presented here, shows the emergence of dynamic co-operativity in terms of a slowing down of the Michaelis-Menten (MM) kinetics resulting in negative co-operativity. For fewer enzymes, dynamic co-operativity emerges due to the combined effects of enzymatic conformational fluctuations and molecular discreteness. The increase in the number of enzymes, however, suppresses the effect of enzymatic conformational fluctuations such that dynamic co-operativity emerges solely due to the discrete changes in the number of reacting species. These results confirm that the turnover kinetics of fluctuating enzyme based on the parallel-pathway MM mechanism switches over to the single-pathway MM mechanism with the increase in the number of enzymes. For large enzyme numbers, convergence to the exact MM equation occurs in the limit of very high substrate concentration as the stochastic kinetics approaches the deterministic behaviour.

  9. Emergence of dynamic cooperativity in the stochastic kinetics of fluctuating enzymes

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Ashutosh; Chatterjee, Sambarta; Nandi, Mintu; Dua, Arti, E-mail: arti@iitm.ac.in [Department of Chemistry, Indian Institute of Technology, Madras, Chennai 600036 (India)

    2016-08-28

    Dynamic co-operativity in monomeric enzymes is characterized in terms of a non-Michaelis-Menten kinetic behaviour. The latter is believed to be associated with mechanisms that include multiple reaction pathways due to enzymatic conformational fluctuations. Recent advances in single-molecule fluorescence spectroscopy have provided new fundamental insights on the possible mechanisms underlying reactions catalyzed by fluctuating enzymes. Here, we present a bottom-up approach to understand enzyme turnover kinetics at physiologically relevant mesoscopic concentrations informed by mechanisms extracted from single-molecule stochastic trajectories. The stochastic approach, presented here, shows the emergence of dynamic co-operativity in terms of a slowing down of the Michaelis-Menten (MM) kinetics resulting in negative co-operativity. For fewer enzymes, dynamic co-operativity emerges due to the combined effects of enzymatic conformational fluctuations and molecular discreteness. The increase in the number of enzymes, however, suppresses the effect of enzymatic conformational fluctuations such that dynamic co-operativity emerges solely due to the discrete changes in the number of reacting species. These results confirm that the turnover kinetics of fluctuating enzyme based on the parallel-pathway MM mechanism switches over to the single-pathway MM mechanism with the increase in the number of enzymes. For large enzyme numbers, convergence to the exact MM equation occurs in the limit of very high substrate concentration as the stochastic kinetics approaches the deterministic behaviour.

  10. Emergence of dynamic cooperativity in the stochastic kinetics of fluctuating enzymes

    Science.gov (United States)

    Kumar, Ashutosh; Chatterjee, Sambarta; Nandi, Mintu; Dua, Arti

    2016-08-01

    Dynamic co-operativity in monomeric enzymes is characterized in terms of a non-Michaelis-Menten kinetic behaviour. The latter is believed to be associated with mechanisms that include multiple reaction pathways due to enzymatic conformational fluctuations. Recent advances in single-molecule fluorescence spectroscopy have provided new fundamental insights on the possible mechanisms underlying reactions catalyzed by fluctuating enzymes. Here, we present a bottom-up approach to understand enzyme turnover kinetics at physiologically relevant mesoscopic concentrations informed by mechanisms extracted from single-molecule stochastic trajectories. The stochastic approach, presented here, shows the emergence of dynamic co-operativity in terms of a slowing down of the Michaelis-Menten (MM) kinetics resulting in negative co-operativity. For fewer enzymes, dynamic co-operativity emerges due to the combined effects of enzymatic conformational fluctuations and molecular discreteness. The increase in the number of enzymes, however, suppresses the effect of enzymatic conformational fluctuations such that dynamic co-operativity emerges solely due to the discrete changes in the number of reacting species. These results confirm that the turnover kinetics of fluctuating enzyme based on the parallel-pathway MM mechanism switches over to the single-pathway MM mechanism with the increase in the number of enzymes. For large enzyme numbers, convergence to the exact MM equation occurs in the limit of very high substrate concentration as the stochastic kinetics approaches the deterministic behaviour.

  11. A kinetic model and simulation of starch saccharification and simultaneous ethanol fermentation by amyloglucosidase and Zymomonas mobilis

    Energy Technology Data Exchange (ETDEWEB)

    Lee, C G [Michigan Univ., Ann Arbor, MI (United States). Dept. of Chemical Engineering; Kim, C H; Rhee, S K [Korea Inst. of Science and Technology, Taejon (Korea, Republic of). Genetic Engineering Research Inst.

    1992-07-01

    A mathematical model is described for the simultaneous saccharification and ethanol fermentation (SSF) of sago starch using amyloglycosidase (AMG) and Zymomonas mobilis. By introducing the degree of polymerization (DP) of oligosaccharides produced from sago starch treated with {alpha}-amylase, a series of Michaelis-Menten equations was obtained. After determining kinetic parameters from the results of simple experiments and from the subsite mapping theory, this model was adapted to simulate the SSF process. The results of simulation for SSF are in good agreement with experimental results. (orig.).

  12. Practical steady-state enzyme kinetics.

    Science.gov (United States)

    Lorsch, Jon R

    2014-01-01

    Enzymes are key components of most biological processes. Characterization of enzymes is therefore frequently required during the study of biological systems. Steady-state kinetics provides a simple and rapid means of assessing the substrate specificity of an enzyme. When combined with site-directed mutagenesis (see Site-Directed Mutagenesis), it can be used to probe the roles of particular amino acids in the enzyme in substrate recognition and catalysis. Effects of interaction partners and posttranslational modifications can also be assessed using steady-state kinetics. This overview explains the general principles of steady-state enzyme kinetics experiments in a practical, rather than theoretical, way. Any biochemistry textbook will have a section on the theory of Michaelis-Menten kinetics, including derivations of the relevant equations. No specific enzymatic assay is described here, although a method for monitoring product formation or substrate consumption over time (an assay) is required to perform the experiments described. © 2014 Elsevier Inc. All rights reserved.

  13. Characterization of dietary Ni uptake in the rainbow trout, Oncorhynchus mykiss.

    Science.gov (United States)

    Leonard, Erin M; Nadella, Sunita R; Bucking, Carol; Wood, Chris M

    2009-07-26

    We characterized dietary Ni uptake in the gastrointestinal tract of rainbow trout using both in vivo and in vitro techniques. Adult trout were fed a meal (3% of body mass) of uncontaminated commercial trout chow, labeled with an inert marker (ballotini beads). In vivo dietary Ni concentrations in the supernatant (fluid phase) of the gut contents averaged from 2 micromoll(-1) to 24 micromoll(-1), and net overall absorption efficiency of dietary Ni was approximately 50% from the single meal, similar to that for the essential metal Cu, adding to the growing evidence of Ni essentiality. The stomach and mid-intestine emerged as important sites of Ni uptake in vivo, accounting for 78.5% and 18.9% of net absorption respectively, while the anterior intestine was a site of net secretion. Most of the stomach uptake occurred in the first 4h. In vitro gut sac studies using radiolabeled Ni (at 30 micromoll(-1)) demonstrated that unidirectional uptake occurred in all segments, with area-weighted rates being highest in the anterior intestine. Differences between in vivo and in vitro results likely reflect the favourable uptake conditions in the stomach, and biliary secretion of Ni in the anterior intestine in vivo. The concentration-dependent kinetics of unidirectional Ni uptake in vitro were biphasic in nature, with a saturable Michaelis-Menten relationship observed at 1-30 micromoll(-1) Ni (K(m) - 11 micromoll(-1), J(max) - 53 pmolcm(-2)h(-1) in the stomach and K(m) - 42 micromoll(-1), J(max) - 215 pmolcm(-2)h(-1) in the mid-intestine), suggesting mediation by a channel or carrier process. A linear uptake relationship was seen at higher concentrations, indicative of simple diffusion. Ni uptake (at 30 micromoll(-1)) into the blood compartment was significantly reduced in the stomach by high Mg (50 mmoll(-1)), and in the mid-intestine by both Mg (50 mmoll(-1)) and Ca (50 mmoll(-1)). In both regions, kinetic analysis demonstrated reductions in J(max) with unchanged K

  14. Tritium uptake kinetics in crayfish (Orconectes immunis)

    International Nuclear Information System (INIS)

    Patrick, P.H.

    1985-06-01

    Uptake of tritiated water (HTO) by Orconectes immunis was investigated under laboratory conditions. Tritium uptake in the tissue-free water fraction (TFWT) was described using an exponential model. When steady-state was reached, the ratio of TFWT to HTO was approximately 0.9. Uptake of tritium in the organically-bound fraction (OBT) proceeded slowly, and had not reached steady-state after 117 days of culture. Although steady-state was never reached, the maximum observed ration of OBT to TFWT in whole animals was approximately 0.6. However, this ratio exceeded unity in the exoskeleton. Specific activity ratios of OBT between crayfish and lettuce (food source) were less than or at unity for various test conditions

  15. Interactions of NH4+ and L-glutamate with NO3- transport processes of non-mycorrhizal Fagus sylvatica roots

    NARCIS (Netherlands)

    Kreuzwieser, J; Herschbach, C; Stulen, [No Value; Wiersema, P; Vaalburg, W; Rennenberg, H

    The processes of NO3- uptake and transport and the effects of NH4+ or L-glutamate on these processes were investigated with excised non-mycorrhizal beech (Fagus sylvatica L,) roots, NO3- net uptake followed uniphasic Michaelis-Menten kinetics in a concentration range of 10 mu M to 1 mM with an

  16. Nitrate transport processes in Fagus-Laccaria-mycorrhizae

    NARCIS (Netherlands)

    Kreuzwieser, J; Stulen, [No Value; Wiersema, P; Vaalburg, W; Rennenberg, H

    2000-01-01

    The contribution of influx and efflux of NO3- on NO3- net uptake has been studied in excised mycorrhizae of 18-20 week old beech (Fagus sylvatica L.) trees. Net uptake rates of NO3- followed uniphasic Michaelis-Menten kinetics in the concentration range between 10 mu M and 1.0 mM external NO3-, with

  17. A century of enzyme kinetic analysis, 1913 to 2013.

    Science.gov (United States)

    Johnson, Kenneth A

    2013-09-02

    This review traces the history and logical progression of methods for quantitative analysis of enzyme kinetics from the 1913 Michaelis and Menten paper to the application of modern computational methods today. Following a brief review of methods for fitting steady state kinetic data, modern methods are highlighted for fitting full progress curve kinetics based upon numerical integration of rate equations, including a re-analysis of the original Michaelis-Menten full time course kinetic data. Finally, several illustrations of modern transient state kinetic methods of analysis are shown which enable the elucidation of reactions occurring at the active sites of enzymes in order to relate structure and function. Copyright © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  18. The kinetics of denitrification in permeable sediments

    DEFF Research Database (Denmark)

    Evrard, Victor; Glud, Ronnie N.; Cook, Perran L. M.

    2013-01-01

    Permeable sediments comprise the majority of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Computational models are increasingly being used to understand the dynamics of denitrification in permeable sediments, which are complex environments...... on sediments taken from six shallow coastal sites in Port Phillip Bay, Victoria, Australia. The results showed that denitrification commenced rapidly (within 30 min) after the onset of anoxia and the kinetics could be well described by Michaelis-Menten kinetics with half saturation constants (apparent K...... in cohesive sediments despite organic carbon contents one order of magnitude lower for the sediments studied here. The ratio of sediment O-2 consumption to V-max was in the range of 0.02-0.09, and was on average much lower than the theoretical ratio of 0.8. As a consequence, models implemented...

  19. Uptake and elimination kinetics of heavy metals by earthworm ...

    African Journals Online (AJOL)

    Earthworm inoculation of petroleum hydrocarbon contaminated soil is thought to catalyze the bioremediation. Most bioremediation studies focus on the petroleum hydrocarbon content and not on the heavy metals. Here, the uptake kinetics of heavy metals by earthworm in used engine oil contaminated soil was investigated.

  20. A Critical View on In Vitro Analysis of P-glycoprotein (P-gp) Transport Kinetics.

    Science.gov (United States)

    Saaby, Lasse; Brodin, Birger

    2017-09-01

    Transport proteins expressed in the different barriers of the human body can have great implications on absorption, distribution, and excretion of drug compounds. Inhibition or saturation of a transporter can potentially alter these absorbtion, distribution, metabolism and elimination properties and thereby also the pharmacokinetic profile and bioavailability of drug compounds. P-glycoprotein (P-gp, ABCB1) is an efflux transporter which is present in most of the barriers of the body, including the small intestine, the blood-brain barrier, the liver, and the kidney. In all these tissues, P-gp may mediate efflux of drug compounds and may also be a potential site for drug-drug interactions. Consequently, there is a need to be able to predict the saturation and inhibition of P-gp and other transporters in vivo. For this purpose, Michaelis-Menten steady-state analysis has been applied to estimate kinetic parameters, such as K m and V max , for carrier-mediated transport, whereas half-maximal inhibitor concentration (IC 50 ) and the disassociation constant for an inhibitor/P-gp complex (K i ) have been determined to estimate P-gp inhibition. This review addresses in vitro methods commonly used to study P-gp transport kinetics and aims at providing a critical evaluation of the application of steady-state Michaelis-Menten analysis of kinetic parameters for substrate/P-gp interactions. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  1. Kinetic Uptake Studies of Powdered Materials in Solution

    Directory of Open Access Journals (Sweden)

    Mohamed H. Mohamed

    2015-06-01

    Full Text Available Challenges exist for the study of time dependent sorption processes for heterogeneous systems, especially in the case of dispersed nanomaterials in solvents or solutions because they are not well suited to conventional batch kinetic experiments. In this study, a comparison of batch versus a one-pot setup in two variable configurations was evaluated for the study of uptake kinetics in heterogeneous (solid/solution systems: (i conventional batch method; (ii one-pot system with dispersed adsorbent in solution with a semi-permeable barrier (filter paper or dialysis tubing for in situ sampling; and (iii one-pot system with an adsorbent confined in a semi-permeable barrier (dialysis tubing or filter paper barrier with ex situ sampling. The sorbent systems evaluated herein include several cyclodextrin-based polyurethane materials with two types of phenolic dyes: p-nitrophenol and phenolphthalein. The one-pot kinetics method with in situ (Method ii or ex situ (Method iii sampling described herein offers significant advantages for the study of heterogeneous sorption kinetics of highly dispersed sorbent materials with particles sizes across a range of dimensions from the micron to nanometer scale. The method described herein will contribute positively to the development of advanced studies for heterogeneous sorption processes where an assessment of the relative uptake properties is required at different experimental conditions. The results of this study will be advantageous for the study of nanomaterials with significant benefits over batch kinetic studies for a wide range of heterogeneous sorption processes.

  2. Stability in a diffusive food chain model with Michaelis-Menten functional response

    DEFF Research Database (Denmark)

    Lin, Zhigui; Pedersen, Michael

    2004-01-01

    This paper deals with the behavior of positive solutions to a reaction-diffusion system with homogeneous Neumann boundary conditions describing a three species food chain. A sufficient condition for the local asymptotical stability is given by linearization and also a sufficient condition...... for the global asymptotical stability is given by a Lyapunov function. Our result shows that the equilibrium solution is globally asymptotically stable if the net birth rate of the first species is big enough and the net death rate of the third species is neither too big nor too small. (C) 2004 Elsevier Ltd. All...

  3. Kinetic parameters of silicon uptake by rice cultivars

    Directory of Open Access Journals (Sweden)

    Priscila Oliveira Martins

    2012-02-01

    Full Text Available Silicon is considered an important chemical element for rice, because it can improve tolerance to biotic and abiotic stress. However, in many situations no positive effect of silicon was observed, probably due to genetic factors. The objective of this research was to monitor Si uptake kinetics and identify responses of rice cultivars in terms of Si uptake capacity and use. The experiment was carried out in a greenhouse of the São Paulo State University (UNESP, Brazil. The experiment was arranged in a completely randomized, factorial design with three replications. that consisted of two rice cultivars and two Si levels. Kinetic parameters (Vmax, Km, and Cmin, root morphology variables, dry matter yield, Si accumulation and levels in shoots and roots, uptake efficiency, utilization efficiency, and root/shoot ratio were evaluated. Higher Si concentrations in the nutrient solution did not increase rice dry matter. The development of the low-affinity silicon uptake system of the rice cultivar 'Caiapó' was better than of 'Maravilha'.

  4. Uptake kinetics of relatively insoluble particles by tracheobronchial lymph nodes

    International Nuclear Information System (INIS)

    Thomas, R.G.

    1976-01-01

    Tracheobronchial lymph nodes accumulate a portion of material deposited in the deep lung following inhalation of relatively insoluble particles. Experiments involving a variety of compounds, inhaled singly or repeatedly, indicate that the kinetics of lymph node uptake are fairly independent of particle characteristics and mammalian species. The buildup per unit weight of nodal tissue compared with that of lung tissue, with time, can be represented by a linear logarithmic function. However, since the scatter in experimental points may be large at any given time after inhalation exposure, a number of different kinetic descriptions of uptake can be derived. The logarithmic pattern of accumulation can be approximated over an extended time range (several years) by use of a combination of first-order kinetics of loss from the lung and of buildup in lymph nodes, but it is recognized that the processes are much more complicated than this treatment would indicate. Clearance (loss) from the lymph nodes is not well defined, but this aspect is discussed in light of the kinetic models presented

  5. Uptake of 3-[125I]iodo-α-methyl-L-tyrosine into colon cancer DLD-1 cells: characterization and inhibitory effect of natural amino acids and amino acid-like drugs

    International Nuclear Information System (INIS)

    Shikano, Naoto; Ogura, Masato; Okudaira, Hiroyuki; Nakajima, Syuichi; Kotani, Takashi; Kobayashi, Masato; Nakazawa, Shinya; Baba, Takeshi; Yamaguchi, Naoto; Kubota, Nobuo; Iwamura, Yukio; Kawai, Keiichi

    2010-01-01

    Introduction: We examined 3-[ 123 I]iodo-α-methyl-L-tyrosine ([ 123 I]IMT) uptake and inhibition by amino acids and amino acid-like drugs in the human DLD-1 colon cancer cell line, to discuss correlation between the inhibition effect and structure. Methods: Expression of relevant neutral amino acid transporters was examined by real-time PCR with DLD-1 cells. The time course of [ 125 I]IMT uptake, contributions of transport systems, concentration dependence and inhibition effects by amino acids and amino acid-like drugs (1 mM) on [ 125 I]IMT uptake were examined. Results: Expression of system L (4F2hc, LAT1 and LAT2), system A (ATA1, ATA2) and system ASC (ASCT1) was strongly detected; system L (LAT3, LAT4) and MCT8 were weakly detected; and B 0 AT was not detected. [ 125 I]IMT uptake in DLD-1 cells involved Na + -independent system L primarily and Na + -dependent system(s). Uptake of [ 125 I]IMT in Na + -free buffer followed Michaelis-Menten kinetics, with a K m of 78 μM and V max of 333 pmol/10 6 cells per minute. Neutral D- and L-amino acids with branched or aromatic large side chains inhibited [ 125 I]IMT uptake. Tyrosine analogues, tryptophan analogues, L-phenylalanine and p-halogeno-L-phenylalanines, and gamma amino acids [including 3,4-dihydroxy-L-phenylalanine (L-DOPA), DL-threo-β-(3,4-dihydroxyphenyl)serine (DOPS), 4-[bis(2-chloroethyl)amino]-L-phenylalanine and 1-(aminomethyl)-cyclohexaneacetic acid] strongly inhibited [ 125 I]IMT uptake, but L-tyrosine methyl ester and R(+)/S(-)-baclofen weakly inhibited uptake. The substrates of system ASC and A did not inhibit [ 125 I]IMT uptake except L-serine and D/L-cysteine. Conclusions: [ 125 I]IMT uptake in DLD-1 cells involves mostly LAT1 and its substrates' (including amino acid-like drugs derived from tyrosine, tryptophan and phenylalanine) affinity to transport via LAT1. Whether transport of gamma amino acid analogues is involved in LAT1 depends on the structure of the group corresponding to the amino acid

  6. Spectral Quasi-Equilibrium Manifold for Chemical Kinetics.

    Science.gov (United States)

    Kooshkbaghi, Mahdi; Frouzakis, Christos E; Boulouchos, Konstantinos; Karlin, Iliya V

    2016-05-26

    The Spectral Quasi-Equilibrium Manifold (SQEM) method is a model reduction technique for chemical kinetics based on entropy maximization under constraints built by the slowest eigenvectors at equilibrium. The method is revisited here and discussed and validated through the Michaelis-Menten kinetic scheme, and the quality of the reduction is related to the temporal evolution and the gap between eigenvalues. SQEM is then applied to detailed reaction mechanisms for the homogeneous combustion of hydrogen, syngas, and methane mixtures with air in adiabatic constant pressure reactors. The system states computed using SQEM are compared with those obtained by direct integration of the detailed mechanism, and good agreement between the reduced and the detailed descriptions is demonstrated. The SQEM reduced model of hydrogen/air combustion is also compared with another similar technique, the Rate-Controlled Constrained-Equilibrium (RCCE). For the same number of representative variables, SQEM is found to provide a more accurate description.

  7. OXYGEN UPTAKE KINETICS IN SPORT, EXERCISE AND MEDICINE

    Directory of Open Access Journals (Sweden)

    David C. Poole

    2005-03-01

    Full Text Available The objective of the book is to discuss the principal determinants of oxygen uptake dynamics which is essential to developing exercise performance and improving quality of life for patients, especially those with cardio-respiratory diseases. A broad review of the current knowledge about this relatively less studied field is provided by this book. Incidentally, it updates the reader about how a person can use his/her aerobic energy system more effectively in order to fatigue gradually and be able to endure more physical activity. It also discusses the effects of exercise training in speeding up oxygen uptake kinetics, and the effects of ageing and a selection of conditions in slowing oxygen dynamics and declining exercise capacity.

  8. Arbuscular mycorrhiza and kinetic parameters of phosphorus absorption by bean plants Micorriza arbuscular e os parâmetros cinéticos de absorção de fósforo pelo feijoeiro

    Directory of Open Access Journals (Sweden)

    Adriana Parada Dias da Silveira

    2004-04-01

    Full Text Available The mechanisms that determine greater P absorption by mycorrhizal plants are still not completely clear, and are attributed, in part, to an increase in the number of absorption sites promoted by the hyphae, and/or to a greater affinity of the colonized hypha or root carriers to P. The effect of mycorrhizae formed by Glomus etunicatum on the kinetic parameters of P absorption by the roots and on P influx in bean plants of the IAC-Carioca cultivar was evaluated, in two distinct plant development periods: at the onset of flowering and at the pod-filling stage (35 and 50 days after sowing, respectively. A mixture of sand and silica (9:1 was utilized as substrate and irrigated with nutrient solution. The kinetics assay was performed by the method of 32P depletion from the solution (depletion curve, using intact plants. Mycorrhization promoted greater growth and P absorption by bean plants, which was more conspicuously observed at the pod-filling stage. Mycorrhizal plants showed higher values of maximum ion uptake rate (Vmax and net P influx at the flowering stage. Lower minimum ion concentration (Cmin and Michaelis-Menten constant (Km values were verified in mycorrhizal plants at the pod-filling stage. Mycorrhizal plants also presented higher net P influx per plant, in both stages. Cmin was the kinetic parameter more intimately related to P absorption, and a significant correlation was obtained between this parameter and shoot P content and accumulation in bean plants.Os mecanismos envolvidos na maior absorção de P pela planta micorrizada ainda não estão totalmente esclarecidos, atribuindo-se, em parte, ao aumento no número de sítios de absorção promovido pela hifa e/ou maior afinidade dos carregadores da hifa ou da raiz colonizada ao P. Avaliou-se o efeito da micorriza formada por Glomus etunicatum nos parâmetros cinéticos da absorção radicular de P e no influxo de P em feijoeiro, cultivar IAC-Carioca, em duas épocas do ciclo da planta

  9. Exertional oxygen uptake kinetics: a stamen of stamina?

    Science.gov (United States)

    Whipp, Brian J; Rossiter, H B; Ward, S A

    2002-04-01

    The fundamental pulmonary O(2) uptake (.VO(2)) response to moderate, constant-load exercise can be characterized as (d.VO(2)/dt)(tau)+Delta.VO(2) (t)=Delta.VO(2SS) where Delta.VO(2SS) is the steady-state response, and tau is the time constant, with the .VO(2) kinetics reflecting intramuscular O(2) uptake (.QO(2)) kinetics, to within 10%. The role of phosphocreatine (PCr) turnover in .QO(2) control can be explored using (31)P-MR spectroscopy, simultaneously with .VO(2). Although tau.VO(2) and tauPCr vary widely among subjects (approx. 20-65 s), they are not significantly different from each other, either at the on- or off-transient. A caveat to interpreting the "well-fit" exponential is that numerous units of similar Delta.VO(2SS) but with a wide tau distribution can also yield a .VO(2) response with an apparent single tau. This tau is, significantly, inversely correlated with lactate threshold and .VO(2max)(but is poorly predictive; a frail stamen, therefore), consistent with tau not characterizing a compartment with uniform kinetics. At higher intensities, the fundamental kinetics become supplemented with a slowly-developing phase, setting .VO(2)on a trajectory towards maximum .VO(2). This slow component is also demonstrable in Delta[PCr]: the decreased efficiency thereby reflecting a predominantly high phosphate-cost of force production rather than a high O(2)-cost of phosphate production. We also propose that the O(2)-deficit for the slow-component is more likely to reflect shifting Delta.VO(2SS) rather than a single one with a single tau.

  10. Enzyme activity and kinetics in substrate-amended river sediments

    Energy Technology Data Exchange (ETDEWEB)

    Duddridge, J E; Wainwright, M

    1982-01-01

    In determining the effects of heavy metals in microbial activity and litter degradation in river sediments, one approach is to determine the effects of these pollutants on sediment enzyme activity and synthesis. Methods to assay amylase, cellulase and urease activity in diverse river sediments are reported. Enzyme activity was low in non-amended sediments, but increased markedly when the appropriate substrate was added, paralleling both athropogenic and natural amendment. Linear relationships between enzyme activity, length of incubation, sample size and substrate concentration were established. Sediment enzyme activity generally obeyed Michaelis-Menton kinetics, but of the three enzymes, urease gave least significant correlation coefficients when the data for substrate concentration versus activity was applied to the Eadie-Hofstee transformation of the Michaelis-Menten equation. K/sub m/ and V/sub max/ for amylase, cellulase and urease in sediments are reported. (JMT)

  11. Tomato root growth and phosphorus absorption kinetics by tomato plants as affected by phosphorus concentration in nutrient solution

    International Nuclear Information System (INIS)

    Fontes, P.C.R.; Barber, S.A.

    1984-01-01

    To evaluate the effects P concentrations in nutrient solution on root growth and on root physiological characteristics involved in P uptake by tomato Lycopersicon esculentum Mill plants, six seedlings were grown in nutrient solution at initial concentrations of 48.5, 97, 194 and 388 μMP until one day before harvest. They were then transferred to solutions with P at 20 μM and 30 μM, and the depletion curves and Michaelis-Menten parameters were determined. The conclusions were that as P supply increased and as the plant P contents are sufficient for maximum growth, the rate of P uptake tends to be lower. The results also indicate that total P uptake by tomato seedlings depends on the amount of root surface area exposed to P. (M.A.C.) [pt

  12. Kinetic characterisation of primer mismatches in allele-specific PCR: a quantitative assessment.

    Science.gov (United States)

    Waterfall, Christy M; Eisenthal, Robert; Cobb, Benjamin D

    2002-12-20

    A novel method of estimating the kinetic parameters of Taq DNA polymerase during rapid cycle PCR is presented. A model was constructed using a simplified sigmoid function to represent substrate accumulation during PCR in combination with the general equation describing high substrate inhibition for Michaelis-Menten enzymes. The PCR progress curve was viewed as a series of independent reactions where initial rates were accurately measured for each cycle. Kinetic parameters were obtained for allele-specific PCR (AS-PCR) amplification to examine the effect of mismatches on amplification. A high degree of correlation was obtained providing evidence of substrate inhibition as a major cause of the plateau phase that occurs in the later cycles of PCR.

  13. Chloroform and trichloroethylene uptake from water into human skin in vitro: Kinetics and risk implications

    International Nuclear Information System (INIS)

    Bogen, K.T.; Keating, G.A.; Vogel, J.S.

    1995-03-01

    A model recently proposed by the US Environmental Protection Agency (EPA) predicts that short-term dermal uptakes of organic environmental water contaminants are proportional to the square root of exposure time. The model appears to underestimate dermal uptake, based on very limited in vivo uptake data obtained primarily using human subjects. To further assess this model, we examined in vitro dermal uptake kinetics for aqueous organic chemicals using accelerator mass spectrometry (AMS). Specifically, we examined the kinetics of in vitro dermal uptake of 14 C-labeled chloroform and trichloroethylene from dilute (5-ppb) aqueous solutions using full-thickness human cadaver skin exposed for (≤1 hr)

  14. NUMERICAL SOLUTION OF STEADY STATE DISPERSION FLOW MODEL FOR LACTOSE-LACTASE HYDROLYSIS WITH DIFFERENT KINETICS IN FIXED BED

    Directory of Open Access Journals (Sweden)

    OLAOSEBIKAN ABIDOYE OLAFADEHAN

    2010-06-01

    Full Text Available A detailed computational procedure for evaluating lactose hydrolysis with immobilized enzyme in a packed bed tubular reactor under dispersion flow conditions is presented. The dispersion flow model for lactose hydrolysis using different kinetics, taking cognizance of external mass transfer resistances, was solved by the method of orthogonal collocation. The reliability of model simulations was tested using experimental data from a laboratory packed bed column, where the -galactosidase of Kluyveromyces fragilis was immobilized on spherical chitosan beads. Comparison of the simulated results with experimental exit conversion shows that the dispersion flow model and using Michaelis-Menten kinetics with competitive product (galactose inhibition are appropriate to interpret the experimental results and simulate the process of lactose hydrolysis in a fixed bed.

  15. Quantification of in vivo metabolic kinetics of hyperpolarized pyruvate in rat kidneys using dynamic 13C MRSI.

    Science.gov (United States)

    Xu, Tao; Mayer, Dirk; Gu, Meng; Yen, Yi-Fen; Josan, Sonal; Tropp, James; Pfefferbaum, Adolf; Hurd, Ralph; Spielman, Daniel

    2011-10-01

    With signal-to-noise ratio enhancements on the order of 10,000-fold, hyperpolarized MRSI of metabolically active substrates allows the study of both the injected substrate and downstream metabolic products in vivo. Although hyperpolarized [1-(13)C]pyruvate, in particular, has been used to demonstrate metabolic activities in various animal models, robust quantification and metabolic modeling remain important areas of investigation. Enzyme saturation effects are routinely seen with commonly used doses of hyperpolarized [1-(13)C]pyruvate; however, most metrics proposed to date, including metabolite ratios, time-to-peak of metabolic products and single exchange rate constants, fail to capture these saturation effects. In addition, the widely used small-flip-angle excitation approach does not correctly model the inflow of fresh downstream metabolites generated proximal to the target slice, which is often a significant factor in vivo. In this work, we developed an efficient quantification framework employing a spiral-based dynamic spectroscopic imaging approach. The approach overcomes the aforementioned limitations and demonstrates that the in vivo (13)C labeling of lactate and alanine after a bolus injection of [1-(13)C]pyruvate is well approximated by saturatable kinetics, which can be mathematically modeled using a Michaelis-Menten-like formulation, with the resulting estimated apparent maximal reaction velocity V(max) and apparent Michaelis constant K(M) being unbiased with respect to critical experimental parameters, including the substrate dose, bolus shape and duration. Although the proposed saturatable model has a similar mathematical formulation to the original Michaelis-Menten kinetics, it is conceptually different. In this study, we focus on the (13)C labeling of lactate and alanine and do not differentiate the labeling mechanism (net flux or isotopic exchange) or the respective contribution of various factors (organ perfusion rate, substrate transport

  16. O2 uptake kinetics during exercise at peak O2 uptake.

    Science.gov (United States)

    Scheuermann, Barry W; Barstow, Thomas J

    2003-11-01

    Compared with moderate- and heavy-intensity exercise, the adjustment of O2 uptake (VO2) to exercise intensities that elicit peak VO2 has received relatively little attention. This study examined the VO2 response of 21 young, healthy subjects (25 +/- 6 yr; mean +/- SD) during cycle ergometer exercise to step transitions in work rate (WR) corresponding to 90, 100, and 110% of the peak WR achieved during a preliminary ramp protocol (15-30 W/min). Gas exchange was measured breath by breath and interpolated to 1-s values. VO2 kinetics were determined by use of a two- or three-component exponential model to isolate the time constant (tau2) as representative of VO2 kinetics and the amplitude (Amp) of the primary fast component independent of the appearance of any VO2 slow component. No difference in VO2 kinetics was observed between WRs (tau90 = 24.7 +/- 9.0; tau100 = 22.8 +/- 6.7; tau110 = 21.5 +/- 9.2 s, where subscripts denote percent of peak WR; P > 0.05); nor in a subgroup of eight subjects was tau2 different from the value for moderate-intensity (exercise (tau2 = 25 +/- 12 s, P > 0.05). As expected, the Amp increased with increasing WRs (Amp90 = 2,089 +/- 548; Amp100 = 2,165 +/- 517; Amp110 = 2,225 +/- 559 ml/min; Amp90 vs. Amp110, P exercise, the gain of the Vo2 response (as deltaVO2/DeltaWR) is reduced for exercise transitions in the severe-intensity domain, but the approach to this gain is well described by a common time constant that is invariant across work intensities. The lower deltaVO2/deltaWR may be due to an insufficient adjustment of the cardiovascular and/or pulmonary systems that determine O2 delivery to the exercising muscles or due to recruitment of motor units with lower oxidative capacity, after the onset of exercise in the severe-intensity domain.

  17. A path-independent integral for the characterization of solute concentration and flux at biofilm detachments

    Science.gov (United States)

    Moran, B.; Kulkarni, S.S.; Reeves, H.W.

    2007-01-01

    A path-independent (conservation) integral is developed for the characterization of solute concentration and flux in a biofilm in the vicinity of a detachment or other flux limiting boundary condition. Steady state conditions of solute diffusion are considered and biofilm kinetics are described by an uptake term which can be expressed in terms of a potential (Michaelis-Menten kinetics). An asymptotic solution for solute concentration at the tip of the detachment is obtained and shown to be analogous to that of antiplane crack problems in linear elasticity. It is shown that the amplitude of the asymptotic solution can be calculated by evaluating a path-independent integral. The special case of a semi-infinite detachment in an infinite strip is considered and the amplitude of the asymptotic field is related to the boundary conditions and problem parameters in closed form for zeroth and first order kinetics and numerically for Michaelis-Menten kinetics. ?? Springer Science+Business Media, Inc. 2007.

  18. nitrogen saturation in stream ecosystems

    OpenAIRE

    Earl, S. R.; Valett, H. M.; Webster, J. R.

    2006-01-01

    The concept of nitrogen (N) saturation has organized the assessment of N loading in terrestrial ecosystems. Here we extend the concept to lotic ecosystems by coupling Michaelis-Menten kinetics and nutrient spiraling. We propose a series of saturation response types, which may be used to characterize the proximity of streams to N saturation. We conducted a series of short-term N releases using a tracer ((NO3)-N-15-N) to measure uptake. Experiments were conducted in streams spanning a gradient ...

  19. Copper uptake kinetics and regulation in a marine fish after waterborne copper acclimation

    International Nuclear Information System (INIS)

    Dang Fei; Zhong Huan; Wang Wenxiong

    2009-01-01

    The uptake kinetics and regulation of copper in a marine predatory fish, the black sea bream Acanthopagrus schlegeli after acclimation to waterborne Cu were examined, using radiotracer techniques. The dissolved Cu uptake followed a linear pattern during the time of exposure, and the calculated uptake rate constant was 6.24 L kg -1 day -1 . The efflux rate constant was 0.091 day -1 following dietary uptake of Cu, and the dietary assimilation efficiency (AE) of Cu varied between 1.7% and 10.9% after the fish were fed with three types of prey (oysters, clams and brine shrimp). After the fish were acclimated at a nominal concentration of 50 μg Cu L -1 for 14 days, the Cu uptake rate and efflux rate constant did not change significantly, but the Cu body concentrations and metallothionein (MT) concentrations in fish tissues increased significantly. Subcellular Cu distributions were also modified. Significant MT induction was observed in response to increased Cu tissue concentrations, indicating that MT rather than the uptake kinetics may play a primary role in Cu regulation during waterborne Cu acclimation in this marine fish. Moreover, the high Cu efflux may also be important in Cu regulation during long-term exposure. Our modeling calculations indicated that dietary uptake was likely to be the main route for Cu bioaccumulation in the fish, and the relative contribution of waterborne and dietary uptake depended on the bioconcentration factor (BCF) of the prey and ingestion rate of fish.

  20. KINETIKA FERMENTASI SELULOSA MURNI OLEH Trichoderma reesi QM 9414 MENJADI GLUKOSA DAN PENERAPANNYA PADA JERAMI PADI BEBAS LIGNIN [Kinetics of Pure Cellulose Fermentation by Trichoderma Reesei QM 9414 to Glucose and Its Application of on Lignin Free Rice Straw

    Directory of Open Access Journals (Sweden)

    M Iyan Sofyan

    2004-12-01

    Full Text Available The objectives of this research were: 1 to determine aeration rate and substrate concentration of pure cellulose to produce maximum glucose by Trichoderma reesei QM 9414 at 30 oC, and agitation 150 rpm; 2 to study the kinetics of pure cellulose fermentation by Trichoderma reesei QM 9414 to glucose and its implication upon fermentation of the lignin free rice straw. The experiment was arranged in factorial randomized complete design in three times replication. Treatments consisted of three levels of aeration (1,00 vvm; 1,5 vvm; 2,0 vvm and three levels of substrate concentration (0,75 ; 1,00 ; 1,25 % w/v. The results showed that at the exponential phase the average specific growth of Trichoderma reesei QM 9414 was 0,05374 hour-1, the maximum glucose product concentration of pure cellulose was 0.1644 gL-1,and the oxygen transfer was 0,0328 mg L-1 hour-1. According to t-test, the kinetics of pure cellulose fermentation model just the same as the lignin free rice straw fermentation.The enzymes produced by Trichoderma reesei QM 9414 in pure cellulose fermentation media followed the Michaelis-Menten model. The enzyme kinetic parameters were the maximum growth rate was 37x10-3 hour-1 and Michaelis-Menten constant was ½ maximum μ =17,5x10-3 hour-1. The volumetric oxygen transfer (KLa using rice straw was 0,0337 mg.hour-1. The value of KLa could be used for conversion from bioreactor at laboratory scale to commercial scale design.

  1. Kinetic Modeling of Arsenic Cycling by a Freshwater Cyanobacterium as Influenced by N:P Ratios: A Potential Biologic Control in an Iron-Limited Drainage Basin

    Science.gov (United States)

    Markley, C. T.; Herbert, B. E.

    2004-12-01

    Elevated As levels are common in South Texas surface waters, where As is derived from the natural weathering of geogenic sources and a byproduct of historical uranium mining. The impacted surface waters of the Nueces River drainage basin supply Lake Corpus Christi (LCC), a major drinking water reservoir for the Corpus Christi area. The soils and sediments of the Nueces River drainage basin generally have low levels of reactive iron (average concentration of 2780 mg/kg), limiting the control of iron oxyhydroxides on As geochemistry and bioavailability. Given these conditions, biologic cycling of As may have a large influence on As fate and transport in LCC. Sediment cores from LCC show evidence for cyanobacterial blooms after reservoir formation based upon stable isotopes, total organic matter and specific elemental correlations. While algae have been shown to accumulate and reduce inorganic As(V), few studies have reported biologic cycling of As by cyanobacteria. Therefore, As(V) uptake, accumulation, reduction, and excretion in a 1.0 μ M As(V) solution by the freshwater cyanobacterium, Anabaena sp. Strain PCC 7120, was measured over time as a function of low, middle and high N:P ratios (1.2, 12, 120) to determine nutrient effects on As cycling by the cyanobacterium. Total As(V) reduction was observed in all three conditions upon completion of the ten-day experiment. Maximum As(V) reduction rates ranged from (0.013 mmol g C-1 day-1) in the low N:P solution to (0.398 mmol g C-1 day-1) in the high N:P solution. Increased cell biomass in the low N:P ratio solution compensated for the low maximum reduction rate to allow total As(V) reduction. Kinetic equations commonly used to model algal-nutrient interactions were utilized in modeling the current data. The Michaelis-Menten enzyme saturation equation modified with a competitive inhibition term adequately modeled As(III) excretion in the high and middle N:P ratio test conditions. The low N:P test condition further

  2. The steady-state kinetics of the NADH-dependent nitrite reductase from Escherichia coli K 12. Nitrite and hydroxylamine reduction.

    Science.gov (United States)

    Jackson, R H; Cole, J A; Cornish-Bowden, A

    1981-01-01

    The reduction of both NO2- and hydroxylamine by the NADH-dependent nitrite reductase of Escherichia coli K 12 (EC 1.6.6.4) appears to follow Michaelis-Menten kinetics over a wide range of NADH concentrations. Substrate inhibition can, however, be detected at low concentrations of the product NAD+. In addition, NAD+ displays mixed product inhibition with respect to NADH and mixed or uncompetitive inhibition with respect to hydroxylamine. These inhibition characteristics are consistent with a mechanism in which hydroxylamine binds during catalysis to a different enzyme form from that generated when NAD+ is released. The apparent maximum velocity with NADH as varied substrate increases as the NAD+ concentration increases from 0.05 to 0.7 mM with 1 mM-NO2- or 100 mM-hydroxylamine as oxidized substrate. This increase is more marked for hydroxylamine reduction than for NO2- reduction. Models incorporating only one binding site for NAD can account for the variation in the Michaelis-Menten parameters for both NADH and hydroxylamine with [NAD+] for hydroxylamine reduction. According to these models, activation of the reaction occurs by reversal of an over-reduction of the enzyme by NADH. If the observed activation of the enzyme by NAD+ derives both from activation of the generation of the enzyme-hydroxylamine complex from the enzyme-NO2- complex during NO2- reduction and from activation of the reduction of the enzyme-hydroxylamine complex to form NH4+, then the variation of Vapp. for NO2- or hydroxylamine with [NAD+] is consistent with the occurrence of the same enzyme-hydroxylamine complex as an intermediate in both reactions. PMID:6279095

  3. Influence of Prolonged Spaceflight on Heart Rate and Oxygen Uptake Kinetics

    Science.gov (United States)

    Hoffmann, U.; Moore, A.; Drescher, U.

    2013-02-01

    During prolonged spaceflight, physical training is used to minimize cardiovascular deconditioning. Measurement of the kinetics of cardiorespiratory parameters, in particular the kinetic analysis of heart rate, respiratory and muscular oxygen uptake, provides useful information with regard to the efficiency and regulation of the cardiorespiratory system. Practically, oxygen uptake kinetics can only be measured at the lung site (V’O2 resp). The dynamics of V’O2 resp, however, is not identical with the dynamics at the site of interest: skeletal muscle. Eight Astronauts were tested pre- and post-flight using pseudo random binary workload changes between 30 and 80 W. Their kinetic responses of heart rate, respiratory as well as muscular V’O2 kinetics were estimated by using time-series analysis. Statistical analysis revealed that the kinetic responses of respiratory as well as muscular V’O2 kinetics are slowed post-flight than pre-flight. Heart rate seems not to be influenced following flight. The influence of other factors (e. g. astronauts’ exercise training) may impact these parameters and is an area for future studies.

  4. Land use/land cover and scale influences on in-stream nitrogen uptake kinetics

    Science.gov (United States)

    Covino, Tim; McGlynn, Brian; McNamara, Rebecca

    2012-06-01

    Land use/land cover change often leads to increased nutrient loading to streams; however, its influence on stream ecosystem nutrient transport remains poorly understood. Given the deleterious impacts elevated nutrient loading can have on aquatic ecosystems, it is imperative to improve understanding of nutrient retention capacities across stream scales and watershed development gradients. We performed 17 nutrient addition experiments on six streams across the West Fork Gallatin Watershed, Montana, USA, to quantify nitrogen uptake kinetics and retention dynamics across stream sizes (first to fourth order) and along a watershed development gradient. We observed that stream nitrogen (N) uptake kinetics and spiraling parameters varied across streams of different development intensity and scale. In more developed watersheds we observed a fertilization affect. This fertilization affect was evident as increased ash-free dry mass, chlorophylla, and ambient and maximum uptake rates in developed as compared to undeveloped streams. Ash-free dry mass, chlorophylla, and the number of structures in a subwatershed were significantly correlated to nutrient spiraling and kinetic parameters, while ambient and average annual N concentrations were not. Additionally, increased maximum uptake capacities in developed streams contributed to low in-stream nutrient concentrations during the growing season, and helped maintain watershed export at low levels during base flow. Our results indicate that land use/land cover change can enhance in-stream uptake of limiting nutrients and highlight the need for improved understanding of the watershed dynamics that control nutrient export across scales and development intensities for mitigation and protection of aquatic ecosystems.

  5. Collective behaviours: from biochemical kinetics to electronic circuits

    Science.gov (United States)

    Agliari, Elena; Barra, Adriano; Burioni, Raffaella; di Biasio, Aldo; Uguzzoni, Guido

    2013-12-01

    In this work we aim to highlight a close analogy between cooperative behaviors in chemical kinetics and cybernetics; this is realized by using a common language for their description, that is mean-field statistical mechanics. First, we perform a one-to-one mapping between paradigmatic behaviors in chemical kinetics (i.e., non-cooperative, cooperative, ultra-sensitive, anti-cooperative) and in mean-field statistical mechanics (i.e., paramagnetic, high and low temperature ferromagnetic, anti-ferromagnetic). Interestingly, the statistical mechanics approach allows a unified, broad theory for all scenarios and, in particular, Michaelis-Menten, Hill and Adair equations are consistently recovered. This framework is then tested against experimental biological data with an overall excellent agreement. One step forward, we consistently read the whole mapping from a cybernetic perspective, highlighting deep structural analogies between the above-mentioned kinetics and fundamental bricks in electronics (i.e. operational amplifiers, flashes, flip-flops), so to build a clear bridge linking biochemical kinetics and cybernetics.

  6. Thallium and potassium uptake kinetics and competition differ between durum wheat and canola.

    Science.gov (United States)

    Renkema, Heidi; Koopmans, Amy; Hale, Beverley; Berkelaar, Edward

    2015-02-01

    Thallium (Tl) is very toxic to mammals but little is known about its accumulation by plants, and it would be useful if prediction of Tl accumulation could be done using potassium (K) accumulation models. The objectives of this study were to compare the uptake kinetics of Tl(+) and K(+), and to determine how readily K(+) can inhibit Tl(+) uptake. Durum wheat (Triticum turgidum L.) and spring canola (Brassica napus L.) were grown hydroponically and exposed to 0-75 μM Tl or 0-250 μM K for up to 150 min (kinetics experiment), or to 0.1 or 10 μM Tl with Tl to K ratios of 1:1 to 1:10,000 for up to 300 min (competition experiment). The rate of uptake of Tl(+) by canola was about three to five times faster than by wheat, while the rate of Tl(+) uptake in wheat was the same as the rate of K(+) uptake by either species. Uptake of Tl(+) was more readily suppressed by K(+) in wheat than in canola. When exposed to 0.1 uM Tl for 300 min with 100 or 1,000 uM K(+), Tl(+) uptake by wheat was reduced by 20 % and 50 %, respectively, while Tl(+) uptake by canola was not reduced. Our results suggest that predicting Tl accumulation using a K accumulation model with a correction factor may be possible for canola, but would be much more difficult for wheat, since uptake of Tl(+) is very sensitive to levels of K(.)

  7. Influence of exercise intensity on skeletal muscle blood flow, O2 extraction and O2 uptake on-kinetics

    DEFF Research Database (Denmark)

    Jones, Andrew M; Krustrup, Peter; Wilkerson, Daryl P

    2012-01-01

    Key points Following the start of low-intensity exercise in healthy humans, it has been established that the kinetics of muscle O(2) delivery is faster than, and does not limit, the kinetics of muscle O(2) uptake. Direct data are lacking, however, on the question of whether O(2) delivery might...... limit O(2) uptake kinetics during high-intensity exercise. In this study, we made frequent measurements of muscle blood flow, arterial-to-venous O(2) difference (a- difference) and O(2) uptake following the onset of multiple transitions of both low-intensity and high-intensity knee-extension exercise...... in the same subjects. We show that although blood flow kinetics is slower for high-intensity compared with low-intensity exercise, this does not result in slower O(2) uptake kinetics. These results indicate that muscle O(2) delivery does not limit O(2) uptake during knee-extension exercise in healthy humans....

  8. Copper uptake kinetics and regulation in a marine fish after waterborne copper acclimation

    Energy Technology Data Exchange (ETDEWEB)

    Dang Fei; Zhong Huan [AMCE and Department of Biology, Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon (Hong Kong); Wang Wenxiong, E-mail: wwang@ust.hk [AMCE and Department of Biology, Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Kowloon (Hong Kong)

    2009-09-14

    The uptake kinetics and regulation of copper in a marine predatory fish, the black sea bream Acanthopagrus schlegeli after acclimation to waterborne Cu were examined, using radiotracer techniques. The dissolved Cu uptake followed a linear pattern during the time of exposure, and the calculated uptake rate constant was 6.24 L kg{sup -1} day{sup -1}. The efflux rate constant was 0.091 day{sup -1} following dietary uptake of Cu, and the dietary assimilation efficiency (AE) of Cu varied between 1.7% and 10.9% after the fish were fed with three types of prey (oysters, clams and brine shrimp). After the fish were acclimated at a nominal concentration of 50 {mu}g Cu L{sup -1} for 14 days, the Cu uptake rate and efflux rate constant did not change significantly, but the Cu body concentrations and metallothionein (MT) concentrations in fish tissues increased significantly. Subcellular Cu distributions were also modified. Significant MT induction was observed in response to increased Cu tissue concentrations, indicating that MT rather than the uptake kinetics may play a primary role in Cu regulation during waterborne Cu acclimation in this marine fish. Moreover, the high Cu efflux may also be important in Cu regulation during long-term exposure. Our modeling calculations indicated that dietary uptake was likely to be the main route for Cu bioaccumulation in the fish, and the relative contribution of waterborne and dietary uptake depended on the bioconcentration factor (BCF) of the prey and ingestion rate of fish.

  9. Uptake and elimination kinetics of metals in soil invertebrates: a review.

    Science.gov (United States)

    Ardestani, Masoud M; van Straalen, Nico M; van Gestel, Cornelis A M

    2014-10-01

    Uptake and elimination kinetics of metals in soil invertebrates are a function of both soil and organism properties. This study critically reviewed metal toxicokinetics in soil invertebrates and its potential use for assessing bioavailability. Uptake and elimination rate constants of different metals are summarized. Invertebrates have different strategies for essential and non-essential metals. As a consequence, different types of models must be applied to describe metal uptake and elimination kinetics. We discuss model parameters for each metal separately and show how they are influenced by exposure concentrations and by physiological properties of the organisms. Soil pH, cation exchange capacity, clay and organic matter content significantly affect uptake rates of non-essential metals in soil invertebrates. For essential metals, kinetics is hardly influenced by soil properties, but rather prone to physiological regulation mechanisms of the organisms. Our analysis illustrates that toxicokinetics can be a valuable measurement to assess bioavailability of soil-bound metals. Copyright © 2014 Elsevier Ltd. All rights reserved.

  10. Determination of kinetic parameters for 123-I thyroid uptake in healthy Japanese

    Science.gov (United States)

    Kusuhara, Hiroyuki; Maeda, Kazuya

    2017-09-01

    The purpose of this study was to compare the kinetic parameters for iodide thyroid accumulation in Japanese today with previously reported values. We determined the thyroid uptake of 123-I at 24 hours after the oral administration in healthy male Japanese without any diet restriction. The mean value was 16.1±5.4%, which was similar or rather lower than those previously reported in Japan (1958-1972). Kinetic model analysis was conducted to obtain the clearance for thyroid uptake from the blood circulation. The thyroid uptake clearance of 123-I was 0.540±0.073 ml/min, which was almost similar to those reported previously. There is no obvious difference in the thyroid uptake for 24 hours, and kinetic parameters in healthy Japanese for these 50 years. The fraction of distributed to the thyroid gland is lower than the ICRP reference man, and such difference must be taken into consideration to estimate the radiation exposure upon Fukushima accident in Japan.

  11. Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction.

    Science.gov (United States)

    Hummel, Scott L; Herald, John; Alpert, Craig; Gretebeck, Kimberlee A; Champoux, Wendy S; Dengel, Donald R; Vaitkevicius, Peter V; Alexander, Neil B

    2016-07-01

    Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Older adults with HF and reduced ejection fraction (n = 25, age 75 ± 7 years) were compared to 25 healthy age- and gender-matched controls. Assessments included a maximal treadmill test for peak oxygen uptake (VO2peak), oxygen uptake kinetics at onset of and on recovery from a submaximal treadmill test, functional mobility testing [Get Up and Go (GUG), Comfortable Gait Speed (CGS), Unipedal Stance (US)], and self-reported physical activity (PA). Compared to controls, HF had worse performance on GUG, CGS, and US, greater delays in submaximal oxygen uptake kinetics, and lower PA. In controls, VO2peak was more strongly associated with functional mobility and PA than submaximal oxygen uptake kinetics. In HF patients, submaximal oxygen uptake kinetics were similarly associated with GUG and CGS as VO2peak, but weakly associated with PA. Based on their mobility performance, older HF patients with reduced ejection fraction are at risk for adverse functional outcomes. In this population, submaximal oxygen uptake measures may be equivalent to VO2 peak in predicting functional mobility, and in addition to being more feasible, may provide better insight into how aerobic function relates to mobility in older adults with HF.

  12. Uptake kinetics of metals by the earthworm Eisenia fetida exposed to field-contaminated soils

    Energy Technology Data Exchange (ETDEWEB)

    Nahmani, Johanne, E-mail: nahmani@univ-metz.f [Laboratoire Interactions Ecotoxicite, Biodiversite, Ecosystemes, CNRS UMR 7146, Universite Paul Verlaine - Metz, Rue du General Delestraint, 57070 Metz (France); Department of Soil Science, School of Human and Environmental Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6DW (United Kingdom); Hodson, Mark E. [Department of Soil Science, School of Human and Environmental Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6DW (United Kingdom); Devin, Simon [Laboratoire Interactions Ecotoxicite, Biodiversite, Ecosystemes, CNRS UMR 7146, Universite Paul Verlaine - Metz, Rue du General Delestraint, 57070 Metz (France); Vijver, Martina G. [Leiden University, Institute of Environmental Sciences (CML), P.O. Box 9518, 2300 RA Leiden (Netherlands)

    2009-10-15

    It is well known that earthworms can accumulate metals. However, most accumulation studies focus on Cd-, Cu-, Pb- or Zn-amended soils, additionally few studies consider accumulation kinetics. Here we model the accumulation kinetics of 18 elements by Eisenia fetida, exposed to 8 metal-contaminated and 2 uncontaminated soils. Tissue metal concentration was determined after 3, 7, 14, 21, 28 and 42 days. Metal elimination rate was important in determining time to reach steady-state tissue metal concentration. Uptake flux to elimination rate ratios showed less variation and lower values for essential than for non-essential metals. In theory kinetic rate constants are dependent only on species and metal. Therefore it should be possible to predict steady-state tissue metal concentrations on the basis of very few measurements using the rate constants. However, our experiments show that it is difficult to extrapolate the accumulation kinetic constants derived using one soil to another. - Earthworm metal uptake and elimination constants derived from a one-compartment model show little systematic variation with soil properties.

  13. Some Investigations on Protease Enzyme Production Kinetics Using Bacillus licheniformis BBRC 100053 and Effects of Inhibitors on Protease Activity

    Directory of Open Access Journals (Sweden)

    Zahra Ghobadi Nejad

    2014-01-01

    Full Text Available Due to great commercial application of protease, it is necessary to study kinetic characterization of this enzyme in order to improve design of enzymatic reactors. In this study, mathematical modeling of protease enzyme production kinetics which is derived from Bacillus licheniformis BBRC 100053 was studied (at 37°C, pH 10 after 73 h in stationary phase, and 150 rpm. The aim of the present paper was to determine the best kinetic model and kinetic parameters for production of protease and calculating Ki (inhibition constant of different inhibitors to find the most effective one. The kinetic parameters Km (Michaelis-Menten constant and Vm (maximum rate were calculated 0.626 mM and 0.0523 mM/min. According to the experimental results, using DFP (diisopropyl fluorophosphate and PMSF (phenylmethanesulfonyl fluoride as inhibitors almost 50% of the enzyme activity could be inhibited when their concentrations were 0.525 and 0.541 mM, respectively. Ki for DFP and PMSF were 0.46 and 0.56 mM, respectively. Kinetic analysis showed that the Lineweaver-Burk model was the best fitting model for protease production kinetics DFP was more effective than PMSF and both of them should be covered in the group of noncompetitive inhibitors.

  14. Complex Reaction Kinetics in Chemistry: A Unified Picture Suggested by Mechanics in Physics

    Directory of Open Access Journals (Sweden)

    Elena Agliari

    2018-01-01

    Full Text Available Complex biochemical pathways can be reduced to chains of elementary reactions, which can be described in terms of chemical kinetics. Among the elementary reactions so far extensively investigated, we recall the Michaelis-Menten and the Hill positive-cooperative kinetics, which apply to molecular binding and are characterized by the absence and the presence, respectively, of cooperative interactions between binding sites. However, there is evidence of reactions displaying a more complex pattern: these follow the positive-cooperative scenario at small substrate concentration, yet negative-cooperative effects emerge as the substrate concentration is increased. Here, we analyze the formal analogy between the mathematical backbone of (classical reaction kinetics in Chemistry and that of (classical mechanics in Physics. We first show that standard cooperative kinetics can be framed in terms of classical mechanics, where the emerging phenomenology can be obtained by applying the principle of least action of classical mechanics. Further, since the saturation function plays in Chemistry the same role played by velocity in Physics, we show that a relativistic scaffold naturally accounts for the kinetics of the above-mentioned complex reactions. The proposed formalism yields to a unique, consistent picture for cooperative-like reactions and to a stronger mathematical control.

  15. Kinetics of Single-Enzyme Reactions on Vesicles: Role of Substrate Aggregation

    Science.gov (United States)

    Zhdanov, Vladimir P.

    2015-03-01

    Enzymatic reactions occurring in vivo on lipid membranes can be influenced by various factors including macromolecular crowding in general and substrate aggregation in particular. In academic studies, the role of these factors can experimentally be clarified by tracking single-enzyme kinetics occurring on individual lipid vesicles. To extend the conceptual basis for such experiments, we analyze herein the corresponding kinetics mathematically with emphasis on the role of substrate aggregation. In general, the aggregation may occur on different length scales. Small aggregates may e.g. contain a few proteins or peptides while large aggregates may be mesoscopic as in the case of lipid domains which can be formed in the membranes composed of different lipids. We present a kinetic model describing comprehensively the effect of aggregation of the former type on the dependence of the reaction rate on substrate membrane concentration. The results obtained with physically reasonable parameters indicate that the aggregation-related deviations from the conventional Michaelis-Menten kinetics may be appreciable. Special Issue Comments: This theoretical article is focused on single-enzyme reactions occurring in parallel with substrate aggregation on individual vesicles. This subject is related to a few Special Issue articles concerning enzyme dynamics6,7 and function8 and mathematical aspects of stochastic kinetics.9

  16. A physiologically based kinetic model for bacterial sulfide oxidation.

    Science.gov (United States)

    Klok, Johannes B M; de Graaff, Marco; van den Bosch, Pim L F; Boelee, Nadine C; Keesman, Karel J; Janssen, Albert J H

    2013-02-01

    In the biotechnological process for hydrogen sulfide removal from gas streams, a variety of oxidation products can be formed. Under natron-alkaline conditions, sulfide is oxidized by haloalkaliphilic sulfide oxidizing bacteria via flavocytochrome c oxidoreductase. From previous studies, it was concluded that the oxidation-reduction state of cytochrome c is a direct measure for the bacterial end-product formation. Given this physiological feature, incorporation of the oxidation state of cytochrome c in a mathematical model for the bacterial oxidation kinetics will yield a physiologically based model structure. This paper presents a physiologically based model, describing the dynamic formation of the various end-products in the biodesulfurization process. It consists of three elements: 1) Michaelis-Menten kinetics combined with 2) a cytochrome c driven mechanism describing 3) the rate determining enzymes of the respiratory system of haloalkaliphilic sulfide oxidizing bacteria. The proposed model is successfully validated against independent data obtained from biological respiration tests and bench scale gas-lift reactor experiments. The results demonstrate that the model is a powerful tool to describe product formation for haloalkaliphilic biomass under dynamic conditions. The model predicts a maximum S⁰ formation of about 98 mol%. A future challenge is the optimization of this bioprocess by improving the dissolved oxygen control strategy and reactor design. Copyright © 2012 Elsevier Ltd. All rights reserved.

  17. Phosphate uptake kinetics for four species of submerged freshwater macrophytes measured by a 33P phosphate radioisotope technique

    DEFF Research Database (Denmark)

    Christiansen, Nina Høj; Andersen, Frede Østergaard; Jensen, Henning S.

    2016-01-01

    Phosphate (Pi) uptake kinetics were determined in shoot and root tissues for four freshwater macrophyte species, Littorella uniflora, Potamogeton perfoliatus, Myriophyllum alterniflorum and Elodea canadensis, using a radioactive 33P phosphate technique. Collection of plant material in the oligotr...

  18. Comparative kinetic analysis of89 Sr,60 Co and65 Zn Uptake by human bone powder

    International Nuclear Information System (INIS)

    Abdel-Fatah, A.T.A.; Essa, M.W.A.; Mohamed, S.A.; Molokhia, M.K.

    1990-01-01

    Human bone powder samples were prepared from recent femurs. The Bone particles range between 30 and 40 MU in diameter. One portion of this powder was prepared fat-free (FFB), the second portion as protein-free (PFB) and the last portion was left as raw bone powder-(RB). The sequence of uptake of 89 Sr by these types of bone powder is : FFB > RB > PFB, while that of 60 Co and 65 Zn is: PFB > FFB > RB. Kinetic analysis of the uptake curves of the 3 isotopes indicated that these processes proceed in 3 distinct steps; very fast initial, moderate intermediate and slow last step. The obtained rates of uptake indicated that : (1) the uptake by PEB is faster in its third step than the other types, (2) the most predominant step in case of 89 Sr and 60 Co is the third step (ion exchange step) while in case of 65 Zn it is the first step (physical adsorption), (3) defatenisation or deproteinisation, in general, inhances the uptake process

  19. Hydrodynamic chronoamperometry for probing kinetics of anaerobic microbial metabolism--case study of Faecalibacterium prausnitzii.

    Science.gov (United States)

    Prévoteau, Antonin; Geirnaert, Annelies; Arends, Jan B A; Lannebère, Sylvain; Van de Wiele, Tom; Rabaey, Korneel

    2015-07-01

    Monitoring in vitro the metabolic activity of microorganisms aids bioprocesses and enables better understanding of microbial metabolism. Redox mediators can be used for this purpose via different electrochemical techniques that are either complex or only provide non-continuous data. Hydrodynamic chronoamperometry using a rotating disc electrode (RDE) can alleviate these issues but was seldom used and is poorly characterized. The kinetics of Faecalibacterium prausnitzii A2-165, a beneficial gut microbe, were determined using a RDE with riboflavin as redox probe. This butyrate producer anaerobically ferments glucose and reduces riboflavin whose continuous monitoring on a RDE provided highly accurate kinetic measurements of its metabolism, even at low cell densities. The metabolic reaction rate increased linearly over a broad range of cell concentrations (9 × 10(4) to 5 × 10(7) cells.mL(-1)). Apparent Michaelis-Menten kinetics was observed with respect to riboflavin (KM = 6 μM; kcat = 5.3 × 10(5) s(-1), at 37 °C) and glucose (KM = 6 μM; kcat = 2.4 × 10(5) s(-1)). The short temporal resolution allows continuous monitoring of fast cellular events such as kinetics inhibition with butyrate. Furthermore, we detected for the first time riboflavin reduction by another potential probiotic, Butyricicoccus pullicaecorum. The ability of the RDE for fast, accurate, simple and continuous measurements makes it an ad hoc tool for assessing bioprocesses at high resolution.

  20. Global Kinetic Analysis of Mammalian E3 Reveals pH-dependent NAD+/NADH Regulation, Physiological Kinetic Reversibility, and Catalytic Optimum*

    Science.gov (United States)

    Moxley, Michael A.; Beard, Daniel A.; Bazil, Jason N.

    2016-01-01

    Mammalian E3 is an essential mitochondrial enzyme responsible for catalyzing the terminal reaction in the oxidative catabolism of several metabolites. E3 is a key regulator of metabolic fuel selection as a component of the pyruvate dehydrogenase complex (PDHc). E3 regulates PDHc activity by altering the affinity of pyruvate dehydrogenase kinase, an inhibitor of the enzyme complex, through changes in reduction and acetylation state of lipoamide moieties set by the NAD+/NADH ratio. Thus, an accurate kinetic model of E3 is needed to predict overall mammalian PDHc activity. Here, we have combined numerous literature data sets and new equilibrium spectroscopic experiments with a multitude of independently collected forward and reverse steady-state kinetic assays using pig heart E3. The latter kinetic assays demonstrate a pH-dependent transition of NAD+ activation to inhibition, shown here, to our knowledge, for the first time in a single consistent data set. Experimental data were analyzed to yield a thermodynamically constrained four-redox-state model of E3 that simulates pH-dependent activation/inhibition and active site redox states for various conditions. The developed model was used to determine substrate/product conditions that give maximal E3 rates and show that, due to non-Michaelis-Menten behavior, the maximal flux is different compared with the classically defined kcat. PMID:26644471

  1. Kinetic analysis of zinc uptake and serosal transfer by vascularly perfused rat intestine

    International Nuclear Information System (INIS)

    Hoadley, J.E.; Leinart, A.S.; Cousins, R.J.

    1987-01-01

    Transport kinetics were examined for uptake of 65 Zn from the lumen and for transport of mucosal 65 Zn subsequent to uptake in the isolated, vascularly perfused intestines of rats fed either a zinc-deficient or zinc-adequate diet. Zinc depletion influenced the intestinal transport of zinc by 1) stimulating a saturable uptake mechanisms, 2) reducing secretion of mucosal 65 Zn into the lumen, and 3) increasing the rate of 65 Zn turnover in a rapidly absorbed mucosal zinc compartment. Uptake of 65 Zn involved both saturable and nonsaturable processes. The saturable process was stimulated by zinc depletion with the apparent maximal transport rate for the saturable mechanism increasing from 60 to 180 nmol Zn x g -1 x 30 min -1 . Most of the 65 Zn taken up was not involved in the short-term secretion or absorption, and mucosal 65 Zn retention was independent of dietary zinc status. Absorption of mucosal 65 Zn was nonsaturable, involved a rapid exchanging zinc compartment, and was stimulated by zinc depletion. The half-life for 65 Zn in this mucosal zinc compartment was ∼ 24 min in the zinc-adequate group and 13 min in the zinc-depleted group

  2. Heavy and toxic metal uptake by mesoporous hypercrosslinked SMA beads: Isotherms and kinetics

    Directory of Open Access Journals (Sweden)

    Renuka Gonte

    2016-09-01

    Full Text Available Hypercrosslinked styrene-maleic acid copolymer beads were used for the removal of metal ions from mimicked industrial effluents. The polymer was characterized by SEM which revealed the presence of a porous network. Carboxyl acid groups of the polymer were identified as active sites for metal uptake. Highly porous surface enhanced metal ion uptake was achieved through a physicochemical process. Equilibrium sorption of metal ions was best described by the Freundlich and Temkin model with R2 > 0.99. Adsorption followed pseudo first and pseudo second order reaction kinetics. Intraparticle diffusion model suggested a three step equilibrium. Desorption was a fast process with ∼90% in 60 min.

  3. Application of Elovich equation on uptake kinetics of 137Cs by living freshwater macrophytes - a short duration laboratory study

    International Nuclear Information System (INIS)

    Jaison, T.J.; Patra, A.K.; Ravi, P.M.; Tripathi, R.M.

    2014-01-01

    Application of Elovich equation on uptake kinetics of 137 Cs by two living macrophytes during controlled experiments on short duration exposure is studied. Compliance to 2 nd order kinetics indicates the mechanism could be chemi-sorption, involving polar functional groups present on the extracelluar surface of the macrophytes. Data analysis suggests that Myriophyllum s. exhibits faster adsorption rate than Hydrilla v. As Myriophyllum s. exhibits better kinetics than Hydrilla v., former could be a better natural adsorbing media for 137 Cs. (author)

  4. Kinetics of zinc uptake and exchange by primary cultures of rat hepatocytes

    International Nuclear Information System (INIS)

    Pattison, S.E.; Cousins, R.J.

    1986-01-01

    The kinetics of 65 Zn 2+ uptake and exchange by hepatocytes in primary culture have been examined in detail to provide a basis for analyzing hormonal regulation of hepatic zinc metabolism. 65 Zn 2+ uptake was found to be a biphasic process. The slow phase represents an exchange between Zn 2+ in the medium and preexisting, intracellular zinc pools. This exchange rate was saturable with a medium zinc concentration of 9.5 microM eliciting one-half the maximum exchange rate and a maximum exchange rate of 9.9 pmol Zn 2+ . min-1 . mg protein-1 in the presence of bovine serum albumin. In the absence of albumin, a secondary, nonsaturable uptake rate was observed. The slow phase was relatively selective, and of the divalent transition metal ions tested, only Cd 2+ and Mn 2+ caused inhibition. The rate of exchange suggests total hepatocyte zinc has a turnover rate of approximately 30 h. The fast phase of 65 Zn 2+ reflects net Zn 2+ accumulation into a labile pool. The initial rates for this process were too fast to be measured accurately, but steady-state measurements allowed determination of the labile pool size. The pool dimensions saturated in the presence [Kapp = 28.6 microM; pool capacity = 0.44 nmol Zn 2+ /mg protein] and absence [Kapp = 11.8 microM; pool capacity = 0.34 nmol Zn 2+ /mg protein] of bovine serum albumin. Kinetics and equilibria of Zn 2+ uptake into the labile pool suggest that the latter acts as a source of Zn 2+ for the slow-exchange phase. Dexamethasone stimulated slow Zn 2+ exchange and also increased the labile pool size. The data suggest physiological factors alter hepatic zinc metabolism by influencing both intracellular Zn 2+ pools

  5. On enzyme kinetic parameters modification of gamma irradiation

    International Nuclear Information System (INIS)

    Ferdes, O.S.; Ferdes, M.; Turcu, G.R.

    1993-01-01

    To elucidate the molecular mechanisms of gamma-ray action on biomolecules there were investigated the modifications in activity and other kinetic parameters for some enzymes irradiated in pure dry state at relative high doses. There were considered bacterial and fungal α-amylases, glucoamylase and Mucor sp. protease irradiated by a 60 Co gamma-ray source in the dose range 1.0-30.0 kGy, at different dose-rates between 0.5-2.0 kGy/h, at room temperature. Considering the enzyme inactivation in this dose range, the dose-effect relationships have an expected form and depend on the irradiation conditions but not significantly on the dose rate. The catalytic properties of enzymes were modified by irradiation. By usual methods it is evidenced a direct correlation between the enzymatic activities, Michaelis-Menten constant, K m , reaction velocities, v, and the irradiation dose. These experimental findings can support a self-consistent theoretical approach on biophysical radiation action on biological active molecules like enzymes. At the same time, some enzyme behaviour to irradiation could be considered like a good biological indicator of radiation response. (Author) 4 Figs., 19 Refs

  6. A simple theory of motor protein kinetics and energetics. II.

    Science.gov (United States)

    Qian, H

    2000-01-10

    A three-state stochastic model of motor protein [Qian, Biophys. Chem. 67 (1997) pp. 263-267] is further developed to illustrate the relationship between the external load on an individual motor protein in aqueous solution with various ATP concentrations and its steady-state velocity. A wide variety of dynamic motor behavior are obtained from this simple model. For the particular case of free-load translocation being the most unfavorable step within the hydrolysis cycle, the load-velocity curve is quasi-linear, V/Vmax = (cF/Fmax-c)/(1-c), in contrast to the hyperbolic relationship proposed by A.V. Hill for macroscopic muscle. Significant deviation from the linearity is expected when the velocity is less than 10% of its maximal (free-load) value--a situation under which the processivity of motor diminishes and experimental observations are less certain. We then investigate the dependence of load-velocity curve on ATP (ADP) concentration. It is shown that the free load Vmax exhibits a Michaelis-Menten like behavior, and the isometric Fmax increases linearly with ln([ATP]/[ADP]). However, the quasi-linear region is independent of the ATP concentration, yielding an apparently ATP-independent maximal force below the true isometric force. Finally, the heat production as a function of ATP concentration and external load are calculated. In simple terms and solved with elementary algebra, the present model provides an integrated picture of biochemical kinetics and mechanical energetics of motor proteins.

  7. Thymidine kinase 2 enzyme kinetics elucidate the mechanism of thymidine-induced mitochondrial DNA depletion.

    Science.gov (United States)

    Sun, Ren; Wang, Liya

    2014-10-07

    Mitochondrial thymidine kinase 2 (TK2) is a nuclear gene-encoded protein, synthesized in the cytosol and subsequently translocated into the mitochondrial matrix, where it catalyzes the phosphorylation of thymidine (dT) and deoxycytidine (dC). The kinetics of dT phosphorylation exhibits negative cooperativity, but dC phosphorylation follows hyperbolic Michaelis-Menten kinetics. The two substrates compete with each other in that dT is a competitive inhibitor of dC phosphorylation, while dC acts as a noncompetitive inhibitor of dT phosphorylation. In addition, TK2 is feedback inhibited by dTTP and dCTP. TK2 also phosphorylates a number of pyrimidine nucleoside analogues used in antiviral and anticancer therapy and thus plays an important role in mitochondrial toxicities caused by nucleoside analogues. Deficiency in TK2 activity due to genetic alterations causes devastating mitochondrial diseases, which are characterized by mitochondrial DNA (mtDNA) depletion or multiple deletions in the affected tissues. Severe TK2 deficiency is associated with early-onset fatal mitochondrial DNA depletion syndrome, while less severe deficiencies result in late-onset phenotypes. In this review, studies of the enzyme kinetic behavior of TK2 enzyme variants are used to explain the mechanism of mtDNA depletion caused by TK2 mutations, thymidine overload due to thymidine phosphorylase deficiency, and mitochondrial toxicity caused by antiviral thymidine analogues.

  8. Lipase-catalyzed synthesis of palmitanilide: Kinetic model and antimicrobial activity study.

    Science.gov (United States)

    Liu, Kuan-Miao; Liu, Kuan-Ju

    2016-01-01

    Enzymatic syntheses of fatty acid anilides are important owing to their wide range of industrial applications in detergents, shampoo, cosmetics, and surfactant formulations. The amidation reaction of Mucor miehei lipase Lipozyme IM20 was investigated for direct amidation of triacylglycerol in organic solvents. The process parameters (reaction temperature, substrate molar ratio, enzyme amount) were optimized to achieve the highest yield of anilide. The maximum yield of palmitanilide (88.9%) was achieved after 24 h of reaction at 40 °C at an enzyme concentration of 1.4% (70 mg). Kinetics of lipase-catalyzed amidation of aniline with tripalmitin has been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The kinetic constants were estimated by using non-linear regression method using enzyme kinetic modules. The enzyme operational stability study showed that Lipozyme IM20 retained 38.1% of the initial activity for the synthesis of palmitanilide (even after repeated use for 48 h). Palmitanilide, a fatty acid amide, exhibited potent antimicrobial activity toward Bacillus cereus. Copyright © 2015 Elsevier Inc. All rights reserved.

  9. THE KINETICS OF THE REACTIONS CATALYZED BY AN ENZYMATIC PREPARATION PRODUCED BY A BACILLUS LICHENIFORMIS STRAIN

    Directory of Open Access Journals (Sweden)

    MONICA DRAGOMIRESCU

    2007-05-01

    Full Text Available Robust immobilization techniques that preserve the activity of biomolecules have manypotential applications. In recent years, a number of new bioimobilisation methods in solgel-derived materials were reported. The interactions between the biomolecule and theinorganic material determine the degree to which the biomolecule retains its nativeproperties. The newer technological developments in the field of immobilizedbiocatalysts can offer the possibility of a wider and more economical exploitation ofbiocatalysts in biological applications, food and feed industry, medicine, and in thedevelopment of bioprocess monitoring devices, like the biosensors.The aim of this study was to obtain immobilized enzymatic preparations by methodswhich affect enzyme conformations and kinetic parameters as less as possible. Weimmobilized the enzymatic preparation with protease activity produced by a Bacilluslicheniformis B 40 local strain by physical bonding on ceramics and entrapment into solgel-derived glasses obtained from tetraethyl orthosilicate (TEOS, deposited in thin layeron a ceramic support (entrapment/deposition. Both physically adsorbed andentrapped/deposited enzymes follow Michaelis-Menten kinetics, similar with the solubleenzyme. In the case of immobilized enzymes, the apparent Michaelis constant, Km, wasgreater than that of the native one, as it was expected. The kinetic parameters indicatethat the enzymatic preparations adsorbed on ceramic support and entrapped/depositedshow less affinity for the substrate, Km being 1.3 and 2.1 times higher than that of thenative enzyme, respectively. The maximum velocity increased also by 3.5 and 7.9 timesrespectively, compared with the free counterpart (according to Lineweaver-Burklinearization.

  10. Kinetics of Oxidation of Metochlopramide withChloramine-T in HClO4 Medium

    Directory of Open Access Journals (Sweden)

    K. M. Meenakshi

    2009-01-01

    Full Text Available The kinetics of oxidation of metochlopramide hydrochloride (MCP with sodium N-chloro p-toluenesulfonamide (CAT in perchloric acid solution has been studied at 313K. The reaction rate shows a first order dependence on [CAT], fractional order on [MCP] and inverse fractional order on [H+]. There is a negative effect of dielectric constant of the solvent. The addition of the reduction product of CAT has no significant effect on the rate. The rate remained unchanged with the variation in the ionic strength of the medium. The reaction fails to induce the polymerization of acrylonitrile. Thermodynamic parameters have been computed by Arrhenius plot. The stoichiometry of the reaction was found to be 1:2 and oxidation products were identified. The Michaelis-Menten type of kinetics has been proposed. CH3C6H4SO2NHCl have been assumed to be the reactive oxidizing species. Thermodynamic parameters were computed by studying reactions at different temperatures. A mechanism consistent with observed kinetics is proposed.

  11. Kinetics of radiolabelled silver uptake and depuration in the gills of rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla)

    DEFF Research Database (Denmark)

    Wood, C.M.; Grosell, M.; Hogstrand, C.

    2002-01-01

    We examined the influence of speciation on the kinetics of silver uptake and deputation in the gills of two freshwater fish, the rainbow trout (Oncorhynchus mykiss) which has high branchial Na+ and Cl- uptake rates and is relatively sensitive to silver, and the European eel (Anguilla anguilla...... labile than from Ag+ exposures, with 1.6-1.8-fold greater loss rates during the fast phases in both species. Differences in branchial silver uptake between eel and trout correlate well with differences in acute toxicity, but are not as large as differences in ion uptake rates. The complex time...

  12. In vitro kinetic studies on the mechanism of oxygen-dependent cellular uptake of copper radiopharmaceuticals

    Energy Technology Data Exchange (ETDEWEB)

    Holland, Jason P; Bell, Stephen G; Wong, Luet-Lok; Dilworth, Jonathan R [Department of Chemistry, University of Oxford, Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1 3TA (United Kingdom); Giansiracusa, Jeffrey H [Department of Mathematics, Mathematical Institute, University of Oxford, 24-29 St Giles' , Oxford, OX1 3LB (United Kingdom)], E-mail: hollanj3@mskcc.org, E-mail: jasonpholland@gmail.com

    2009-04-07

    The development of hypoxia-selective radiopharmaceuticals for use as therapeutic and/or imaging agents is of vital importance for both early identification and treatment of cancer and in the design of new drugs. Radiotracers based on copper for use in positron emission tomography have received great attention due to the successful application of copper(II) bis(thiosemicarbazonato) complexes, such as [{sup 60/62/64}Cu(II)ATSM] and [{sup 60/62/64}Cu(II)PTSM], as markers for tumour hypoxia and blood perfusion, respectively. Recent work has led to the proposal of a revised mechanism of hypoxia-selective cellular uptake and retention of [Cu(II)ATSM]. The work presented here describes non-steady-state kinetic simulations in which the reported pO{sub 2}-dependent in vitro cellular uptake and retention of [{sup 64}Cu(II)ATSM] in EMT6 murine carcinoma cells has been modelled by using the revised mechanistic scheme. Non-steady-state (NSS) kinetic analysis reveals that the model is in very good agreement with the reported experimental data with a root-mean-squared error of less than 6% between the simulated and experimental cellular uptake profiles. Estimated rate constants are derived for the cellular uptake and washout (k{sub 1} = 9.8 {+-} 0.59 x 10{sup -4} s{sup -1} and k{sub 2} = 2.9 {+-} 0.17 x 10{sup -3} s{sup -1}), intracellular reduction (k{sub 3} = 5.2 {+-} 0.31 x 10{sup -2} s{sup -1}), reoxidation (k{sub 4} = 2.2 {+-} 0.13 mol{sup -1} dm{sup 3} s{sup -1}) and proton-mediated ligand dissociation (k{sub 5} = 9.0 {+-} 0.54 x 10{sup -5} s{sup -1}). Previous mechanisms focused on the reduction and reoxidation steps. However, the data suggest that the origins of hypoxia-selective retention may reside with the stability of the copper(I) anion with respect to protonation and ligand dissociation. In vitro kinetic studies using the nicotimamide adenine dinucleotide (NADH)-dependent ferredoxin reductase enzyme PuR isolated from the bacterium Rhodopseudomonas palustris have

  13. Training-induced acceleration of oxygen uptake kinetics in skeletal muscle: the underlying mechanisms.

    Science.gov (United States)

    Zoladz, J A; Korzeniewski, B; Grassi, B

    2006-11-01

    It is well known that the oxygen uptake kinetics during rest-to-work transition (V(O2) on-kinetics) in trained subjects is significantly faster than in untrained individuals. It was recently postulated that the main system variable that determines the transition time (t(1/2)) of the V(O2) on-kinetics in skeletal muscle, at a given moderate ATP usage/work intensity, and under the assumption that creatine kinase reaction works near thermodynamic equilibrium, is the absolute (in mM) decrease in [PCr] during rest-to-work transition. Therefore we postulate that the training-induced acceleration of the V(O2) on-kinetics is a marker of an improvement of absolute metabolic stability in skeletal muscles. The most frequently postulated factor responsible for enhancement of muscle metabolic stability is the training-induced increase in mitochondrial proteins. However, the mechanism proposed by Gollnick and Saltin (1982) can improve absolute metabolic stability only if training leads to a decrease in resting [ADP(free)]. This effect is not observed in many examples of training causing an acceleration of the V(O2) on-kinetics, especially in early stages of training. Additionally, this mechanism cannot account for the significant training-induced increase in the relative (expressed in % or as multiples of the resting values) metabolic stability at low work intensities, condition in which oxidative phosphorylation is not saturated with [ADP(free)]. Finally, it was reported that in the early stage of training, acceleration in the V(O2) on-kinetics and enhancement of muscle metabolic stability may precede adaptive responses in mitochondrial enzymes activities or mitochondria content. We postulate that the training-induced acceleration in the V(O2) on-kinetics and the improvement of the metabolite stability during moderate intensity exercise in the early stage of training is mostly caused by an intensification of the "parallel activation" of ATP consumption and ATP supply pathways

  14. Kinetic analysis of enzyme systems with suicide substrate in the presence of a reversible competitive inhibitor, tested by simulated progress curves.

    Science.gov (United States)

    Moruno-Dávila, M A; Garrido-del Solo, C; García-Moreno, M; Havsteen, B H; Garcia-Sevilla, F; Garcia-Cánovas, F; Varón, R

    2001-02-01

    The use of suicide substrates remains a very important and useful method in enzymology for studying enzyme mechanisms and designing potential drugs. Suicide substrates act as modified substrates for the target enzymes and bind to the active site. Therefore the presence of a competitive reversible inhibitor decreases the rate of substrate-induced inactivation and protects the enzyme from this inactivation. This lowering on the inactivation rate has evident physiological advantages, since it allows the easy acquisition of experimental data and facilitates kinetic data analysis by providing another variable (inhibitor concentration). However despite the importance of the simultaneous action of a suicide substrate and a competitive reversible inhibition, to date no corresponding kinetic analysis has been carried out. Therefore we present a general kinetic analysis of a Michaelis-Menten reaction mechanism with double inhibition caused by both, a suicide substrate and a competitive reversible inhibitor. We assume rapid equilibrium of the reversible reaction steps involved, while the time course equations for the reaction product have been derived with the assumption of a limiting enzyme. The goodness of the analytical solutions has been tested by comparison with the simulated curves obtained by numerical integration. A kinetic data analysis to determine the corresponding kinetic parameters from the time progress curve of the product is suggested. In conclusion, we present a complete kinetic analysis of an enzyme reaction mechanism as described above in an attempt to fill a gap in the theoretical treatment of this type of system.

  15. Can differences in phosphorus uptake kinetics explain the distribution of cattail and sawgrass in the Florida Everglades?

    Directory of Open Access Journals (Sweden)

    McKee Karen L

    2010-02-01

    Full Text Available Abstract Background Cattail (Typha domingensis has been spreading in phosphorus (P enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense. Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades. Results Apparent P uptake kinetics were measured for intact plants of Cladium and Typha acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in Typha than in Cladium and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was two-fold higher in Typha than in Cladium, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As Cladium had a greater proportion of its biomass allocated to roots, the overall uptake capacity of the two species at high P did not differ. At low P availability, Typha increased biomass allocation to roots more than Cladium. Both species also adjusted their P uptake kinetics, but Typha more so than Cladium. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for Cladium and a ten-fold higher uptake for Typha. Conclusions Both Cladium and Typha adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, Typha adjusts P uptake kinetics and also increases allocation to roots more so than Cladium, thereby improving both efficiency and capacity of P uptake. Cladium has less need to adjust P uptake kinetics because it is already efficient at acquiring P from peat soils (e.g., through secretion of phosphatases, symbiosis with arbuscular mycorrhizal fungi, nutrient conservation growth

  16. Uptake kinetics and nanotoxicity of silica nanoparticles are cell type dependent.

    Science.gov (United States)

    Blechinger, Julia; Bauer, Alexander T; Torrano, Adriano A; Gorzelanny, Christian; Bräuchle, Christoph; Schneider, Stefan W

    2013-12-09

    In this study, it is shown that the cytotoxic response of cells as well as the uptake kinetics of nanoparticles (NPs) is cell type dependent. We use silica NPs with a diameter of 310 nm labeled with perylene dye and 304 nm unlabeled particles to evaluate cell type-dependent uptake and cytotoxicity on human vascular endothelial cells (HUVEC) and cancer cells derived from the cervix carcinoma (HeLa). Besides their size, the particles are characterized concerning homogeneity of the labeling and their zeta potential. The cellular uptake of the labeled NPs is quantified by imaging the cells via confocal microscopy in a time-dependent manner, with subsequent image analysis via a custom-made and freely available digital method, Particle_in_Cell-3D. We find that within the first 4 h of interaction, the uptake of silica NPs into the cytoplasm is up to 10 times more efficient in HUVEC than in HeLa cells. Interestingly, after 10 or 24 h of interaction, the number of intracellular particles for HeLa cells by far surpasses the one for HUVEC. Inhibitor studies show that these endothelial cells internalize 310 nm SiO₂ NPs via the clathrin-dependent pathway. Remarkably, the differences in the amount of taken up NPs are not directly reflected by the metabolic activity and membrane integrity of the individual cell types. Interaction with NPs leads to a concentration-dependent decrease in mitochondrial activity and an increase in membrane leakage for HUVEC, whereas HeLa cells show only a reduced mitochondrial activity and no membrane leakage. In addition, silica NPs lead to HUVEC cell death while HeLa cells survive. These findings indicate that HUVEC are more sensitive than HeLa cells upon silica NP exposure. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. The effect of 17-AAG on iodine uptake kinetics of NIS-transfected anaplastic thyroid cancer

    International Nuclear Information System (INIS)

    Wang Renfei; Tan Jian; Li Wei; Meng Zhaowei; Zheng Wei

    2012-01-01

    Objective: To investigate the effect of 17-allylamino-17-demethoxy geldanamycin (17-AAG) on iodine uptake kinetics of NIS-transfected anaplastic thyroid cancer (ATC) cells. Methods: Lipofection was used to transfect the recombinant plasmid, namely pcDNA3.1-NIS, into FRO cells (ATC cell line). A stable cell line NIS-FRO was obtained by G418 resistance selection. 125 I was added into the medium, and influx and efflux experiments were performed. Different time-radioactivity curves were drawn, and further analysis was performed between the non-transfected cells (the control group) and NIS-FRO cells treated with 1 μmol/L 17-AAG for 24 h. Student's t-test was used to analyze the data. Results: The iodine uptake ability of the NIS-FRO cells was significantly higher than that of the FRO cells (about 10.68 times, t=45.329, P<0.001). However, 125 I out-flowed rapidly when removed from the medium, and the retention rate of 125 I in the NIS-FRO cells was only 10.5% of the initial amount after 30 rin. After treatment with 1 μmol/L 17-AAG for 24 h, the 125 I uptake ability of NIS-FRO cells further increased. During the 20-60 min incubation with 125 I, the iodine uptake ability of 17-AAG treated NIS-FRO cells increased significantly with radioactive counts of 31771.8- 54815.5 per minute,which was much higher than that of the control group (24020.3-41293.8 per minute; t=3.096, 4.275, 3.055, 4.292 and 5.496, respectively, all P<0.05). The iodine uptake ability increased about 24.8%-35.5%. Furthermore, 5-30 min after removing the medium, the retention rates of 125 I in the 17-AAG treated NIS-FRO cells were significantly increased compared with those of the control group (32.7%-85.2% vs 10.5%-56.8%; t=22.801, 13.096, 19.631, 38.205, 43.519, 29.322, respectively, all P<0.01), and 125 I efflux was reduced. After 30 min, 125 I retention rate of the treatment group was 32.7%, which was 3.1 times higher than that of the control group. Conclusion: The iodine uptake ability can be

  18. Optimizing electrode-attached redox-peptide systems for kinetic characterization of protease action on immobilized substrates. Observation of dissimilar behavior of trypsin and thrombin enzymes.

    Science.gov (United States)

    Anne, Agnès; Chovin, Arnaud; Demaille, Christophe

    2012-06-12

    In this work, we experimentally address the issue of optimizing gold electrode attached ferrocene (Fc)-peptide systems for kinetic measurements of protease action. Considering human α-thrombin and bovine trypsin as proteases of interest, we show that the recurring problem of incomplete cleavage of the peptide layer by these enzymes can be solved by using ultraflat template-stripped gold, instead of polished polycrystalline gold, as the Fc-peptide bearing electrode material. We describe how these fragile surfaces can be mounted in a rotating disk configuration so that enzyme mass transfer no longer limits the overall measured cleavage kinetics. Finally, we demonstrate that, once the system has been optimized, in situ real-time cyclic voltammetry monitoring of the protease action can yield high-quality kinetic data, showing no sign of interfering effects. The cleavage progress curves then closely match the Langmuirian variation expected for a kinetically controlled surface process. Global fit of the progress curves yield accurate values of the peptide cleavage rate for both trypsin and thrombin. It is shown that, whereas trypsin action on the surface-attached peptide closely follows Michaelis-Menten kinetics, thrombin displays a specific and unexpected behavior characterized by a nearly enzyme-concentration-independent cleavage rate in the subnanomolar enzyme concentration range. The reason for this behavior has still to be clarified, but its occurrence may limit the sensitivity of thrombin sensors based on Fc-peptide layers.

  19. Exploring between the extremes: conversion-dependent kinetics of phosphite-modified hydroformylation catalysis.

    Science.gov (United States)

    Kubis, Christoph; Selent, Detlef; Sawall, Mathias; Ludwig, Ralf; Neymeyr, Klaus; Baumann, Wolfgang; Franke, Robert; Börner, Armin

    2012-07-09

    The kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a rhodium monophosphite catalyst has been studied in detail. Time-dependent concentration profiles covering the entire olefin conversion range were derived from in situ high-pressure FTIR spectroscopic data for both, pure organic components and catalytic intermediates. These profiles fit to Michaelis-Menten-type kinetics with competitive and uncompetitive side reactions involved. The characteristics found for the influence of the hydrogen concentration verify that the pre-equilibrium towards the catalyst substrate complex is not established. It has been proven experimentally that the hydrogenolysis of the intermediate acyl complex remains rate limiting even at high conversions when the rhodium hydride is the predominant resting state and the reaction is nearly of first order with respect to the olefin. Results from in situ FTIR and high-pressure (HP) NMR spectroscopy and from DFT calculations support the coordination of only one phosphite ligand in the dominating intermediates and a preferred axial position of the phosphite in the electronically saturated, trigonal bipyramidal (tbp)-structured acyl rhodium complex. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Role of conformational dynamics in kinetics of an enzymatic cycle in a nonequilibrium steady state

    Science.gov (United States)

    Min, Wei; Xie, X. Sunney; Bagchi, Biman

    2009-08-01

    Enzyme is a dynamic entity with diverse time scales, ranging from picoseconds to seconds or even longer. Here we develop a rate theory for enzyme catalysis that includes conformational dynamics as cycling on a two-dimensional (2D) reaction free energy surface involving an intrinsic reaction coordinate (X) and an enzyme conformational coordinate (Q). The validity of Michaelis-Menten (MM) equation, i.e., substrate concentration dependence of enzymatic velocity, is examined under a nonequilibrium steady state. Under certain conditions, the classic MM equation holds but with generalized microscopic interpretations of kinetic parameters. However, under other conditions, our rate theory predicts either positive (sigmoidal-like) or negative (biphasic-like) kinetic cooperativity due to the modified effective 2D reaction pathway on X-Q surface, which can explain non-MM dependence previously observed on many monomeric enzymes that involve slow or hysteretic conformational transitions. Furthermore, we find that a slow conformational relaxation during product release could retain the enzyme in a favorable configuration, such that enzymatic turnover is dynamically accelerated at high substrate concentrations. The effect of such conformation retainment in a nonequilibrium steady state is evaluated.

  1. Submaximal oxygen uptake kinetics, functional mobility, and physical activity in older adults with heart failure and reduced ejection fraction

    OpenAIRE

    Hummel, Scott L; Herald, John; Alpert, Craig; Gretebeck, Kimberlee A; Champoux, Wendy S; Dengel, Donald R; Vaitkevicius, Peter V; Alexander, Neil B

    2016-01-01

    Background Submaximal oxygen uptake measures are more feasible and may better predict clinical cardiac outcomes than maximal tests in older adults with heart failure (HF). We examined relationships between maximal oxygen uptake, submaximal oxygen kinetics, functional mobility, and physical activity in older adults with HF and reduced ejection fraction. Methods Older adults with HF and reduced ejection fraction (n = 25, age 75 ? 7 years) were compared to 25 healthy age- and gender-matched cont...

  2. In-stream nutrient uptake kinetics along stream size and development gradients in a rapidly developing mountain resort watershed

    Science.gov (United States)

    Covino, T.; McGlynn, B.; McNamarra, R.; Gardner, K.

    2012-04-01

    Land use / land cover (LULC) change including mountain resort development often lead to increased nutrient loading to streams, however the potential influence on stream ecosystem nutrient uptake kinetics and transport remain poorly understood. Given the deleterious impacts elevated nutrient loading can have on aquatic ecosystems, it is imperative to improve understanding of nutrient retention capacities across stream scales and watershed development intensities. We performed seventeen nutrient addition experiments on six streams across the West Fork Gallatin Watershed, Montana, USA, to quantify nitrogen (N) uptake kinetics and retention dynamics across stream sizes (1st to 4th order) and along a mountain resort development gradient. We observed that stream N uptake kinetics and spiraling parameters varied across streams of different development intensity and scale. In more developed watersheds we observed a fertilization affect, however, none of the streams exhibited saturation with respect to N. Additionally, we observed that elevated loading led to increased biomass and retentive capacities in developed streams that helped maintain export at low levels during baseflow. Our results indicate that LULC can enhance in-stream uptake of limiting nutrients and highlight the value of characterizing uptake kinetic curves from ambient to saturation.

  3. Gymnasium-based unsupervised exercise maintains benefits in oxygen uptake kinetics obtained following supervised training in type 2 diabetes.

    Science.gov (United States)

    Macananey, Oscar; O'Shea, Donal; Warmington, Stuart A; Green, Simon; Egaña, Mikel

    2012-08-01

    Supervised exercise (SE) in patients with type 2 diabetes improves oxygen uptake kinetics at the onset of exercise. Maintenance of these improvements, however, has not been examined when supervision is removed. We explored if potential improvements in oxygen uptake kinetics following a 12-week SE that combined aerobic and resistance training were maintained after a subsequent 12-week unsupervised exercise (UE). The involvement of cardiac output (CO) in these improvements was also tested. Nineteen volunteers with type 2 diabetes were recruited. Oxygen uptake kinetics and CO (inert gas rebreathing) responses to constant-load cycling at 50% ventilatory threshold (V(T)), 80% V(T), and mid-point between V(T) and peak workload (50% Δ) were examined at baseline (on 2 occasions) and following each 12-week training period. Participants decided to exercise at a local gymnasium during the UE. Thirteen subjects completed all the interventions. The time constant of phase 2 of oxygen uptake was significantly faster (p exercise maintained benefits in oxygen uptake kinetics obtained during a supervised exercise in subjects with diabetes, and these benefits were associated with a faster dynamic response of heart rate after training.

  4. COMPARISON OF OXYGEN UPTAKE KINETICS AND OXYGEN DEFICIT IN SEVERELY OVERWEIGHT AND NORMAL WEIGHT ADOLESCENT FEMALES

    Directory of Open Access Journals (Sweden)

    Mark Loftin

    2005-12-01

    Full Text Available The purpose of this study was to determine if differences in oxygen uptake kinetics and oxygen deficit existed between normal weight and severely overweight adolescent girls. Subjects included 10 normal weight and 8 severely overweight girls. The participants performed a leg cycling VO2 peak test and a constant load leg cycling test at 80% of the ventilatory threshold (T-vent. In the constant workload test O2 kinetics as indicated by Phase I (VO2 L at 20 sec and Phase II time constants (t were determined. Also, the O2 deficit (VO2 L was measured. As expected significant differences were noted in body composition and VO2 peak relative to mass with normal weight body mass averaging 55.3 ± 7.0 kg, severely overweight 90.5 ± 18.0 kg, % fat normal weight 27.3 ± 3.9%, severely overweight 49.7 ± 4.9% and VO2 peak (ml·kg-1·min-1 normal weight 32.0 ± 2.7 and severely overweight 22.0 ± 5.3. VO2 peak (l·min-1 and T-vent (%VO2 max were similar between groups. Results revealed similar O2 kinetic responses between groups; phase I kinetics normal weight 0.72 ± 0.15 L; severely overweight 0.75 ± 0.13L, phase II (t normal weight 41.5 ± 21.3 sec; severely overweight 33.9 ± 22.7 sec. However, the O2 deficit was significantly higher in the severely overweight (0.75 ± 0.15L when compared to the normal weight group (0.34 ± 0.13L. Correlations ranged from r = -0.15 to 0.51 between VO2 peak (L·min-1 or fat weight and phase I, t and O2 deficit. These data generally support previous research concerning the independence of O2 uptake response and body size

  5. Oxygen Uptake Kinetics Is Slower in Swimming Than Arm Cranking and Cycling during Heavy Intensity

    Science.gov (United States)

    Sousa, Ana; Borrani, Fabio; Rodríguez, Ferran A.; Millet, Grégoire P.

    2017-01-01

    Oxygen uptake (V·O2) kinetics has been reported to be influenced by the activity mode. However, only few studies have compared V·O2 kinetics between activities in the same subjects in which they were equally trained. Therefore, this study compared the V·O2 kinetics response to swimming, arm cranking, and cycling within the same group of subjects within the heavy exercise intensity domain. Ten trained male triathletes (age 23.2 ± 4.5 years; height 180.8 ± 8.3 cm; weight 72.3 ± 6.6 kg) completed an incremental test to exhaustion and a 6-min heavy constant-load test in the three exercise modes in random order. Gas exchange was measured by a breath-by-breath analyzer and the on-transient V·O2 kinetics was modeled using bi-exponential functions. V·O2peak was higher in cycling (65.6 ± 4.0 ml·kg−1·min−1) than in arm cranking or swimming (48.7 ± 8.0 and 53.0 ± 6.7 ml·kg−1·min−1; P kinetics were slower in swimming (τ1 = 31.7 ± 6.2 s) than in arm cranking (19.3 ± 4.2 s; P = 0.001) and cycling (12.4 ± 3.7 s; P = 0.001). The amplitude of the primary component was lower in both arm cranking and swimming (21.9 ± 4.7 and 28.4 ± 5.1 ml·kg−1·min−1) compared with cycling (39.4 ± 4.1 ml·kg−1·min−1; P = 0.001). Although the gain of the primary component was higher in arm cranking compared with cycling (15.3 ± 4.2 and 10.7 ± 1.3 ml·min−1·W−1; P = 0.02), the slow component amplitude, in both absolute and relative terms, did not differ between exercise modes. The slower V·O2 kinetics during heavy-intensity swimming is exercise-mode dependent. Besides differences in muscle mass and greater type II muscle fibers recruitment, the horizontal position adopted and the involvement of trunk and lower-body stabilizing muscles could be additional mechanisms that explain the differences between exercise modalities. PMID:28919863

  6. Enzymatic Synthesis of Furfuryl Alcohol Ester with Oleic Acid by Candida antarctica Lipase B and Its Kinetic Study

    Science.gov (United States)

    Sengupta, Avery; Dey, Tanmoy; Ghosh, Mahua; Ghosh, Jaydip; Ghosh, Santinath

    2012-08-01

    This study investigated the successful enzymatic production of furfuryl oleate and its detailed kinetic study by Michaelis-Menten model. Esterification of oleic acid and furfuryl alcohol by Candida antarctica lipase B (Novozym 435 preparation) in a solvent free system was studied in the present work at 1:1 molar ratio of furfuryl alcohol and oleic acid. About 99 % conversion (on the basis of oleic acid) has been achieved within 6 h at 5 % enzyme concentration. Ping-pong bi-bi mechanism (inhibition phenomenon taken into account) was applied to describe the ratios as a complex kinetic model. The kinetic parameters were determined using MATLAB language programme. The two initial rate constants KA and KB respectively were found out by different progress curves plotted with the help of MATLAB language programme. It was concluded from the results that furfuryl alcohol considerably inhibited the enzymatic reaction while oleic acid had negligible inhibitory effect. It was clearly seen that the initial rate was increased with the increase in the furfuryl alcohol concentration until 2 M/L after which there was a drop in the initial rate depicting the inhibitory effect of furfuryl alcohol. Surprisingly, it has been observed that addition of 0.1 mol of product activated the esterification reaction. Finally, the model was found to be statistically fitting well with the experimental data.

  7. Effects of vehicle on the uptake and elimination kinetics of capsaicinoids in human skin in vivo

    International Nuclear Information System (INIS)

    Pershing, Lynn K.; Reilly, Christopher A.; Corlett, Judy L.; Crouch, Dennis J.

    2004-01-01

    While the physiologic and molecular effects of capsaicinoids have been extensively studied in various model systems by a variety of administration routes, little is known about the uptake and elimination kinetic profiles in human skin following topical exposure. The present study evaluated the uptake and elimination kinetics of capsaicinoids in human stratum corneum following a single topical exposure to 3% solutions containing 55% capsaicin, 35% dihydrocapsaicin, and 10% other analogues prepared in three vehicles: mineral oil (MO), propylene glycol (PG), and isopropyl alcohol (IPA). Capsaicinoid solutions were evaluated simultaneously in a random application pattern on the volar forearms of 12 subjects using a small, single 150-μg dose. Capsaicin and dihydrocapsaicin were recovered from human skin using commercial adhesive discs to harvest stratum corneum from treated sites. Capsaicinoids were extracted from the stratum corneum-adhesive discs and quantified by liquid chromatography/mass spectroscopy (LC/MS). Both capsaicinoids were detected in stratum corneum 1 min after application with all vehicles and achieved a pseudo-steady state shortly thereafter. IPA delivered three times greater capsaicin and dihydrocapsaicin into the human stratum corneum than PG or MO at all time points investigated. The C max of capsaicin in IPA, PG, and MO was 16.1, 6.2, and 6.5 μg, respectively. The dihydrocapsaicin content was 60% of capsaicin with all vehicles. The estimated T half of capsaicin and dihydrocapsaicin in the three vehicles was similar (24 h). Thus, maximal cutaneous capsaicinoid concentrations were achieved quickly in the human stratum corneum and were concentration and vehicle dependent. In contrast, capsaicinoid half-life was long and vehicle independent

  8. Effect of phosphorus stress on Microcystis aeruginosa growth and phosphorus uptake.

    Directory of Open Access Journals (Sweden)

    Sajeela Ghaffar

    Full Text Available This study was designed to advance understanding of phosphorus regulation of Microcystis aeruginosa growth, phosphorus uptake and storage in changing phosphorus (P conditions as would occur in lakes. We hypothesized that Microcystis growth and nutrient uptake would fit classic models by Monod, Droop, and Michaelis-Menten in these changing conditions. Microcystis grown in luxury nutrient concentrations was transferred to treatments with phosphorus concentrations ranging from 0-256 μg P∙L-1 and luxury nitrogen. Dissolved phosphorus concentration, cell phosphorus quota, P uptake rate and cell densities were measured at day 3 and 6. Results showed little relationship to predicted models. Microcystis growth was asymptotically related to P treatment from day 0-3, fitting Monod model well, but negatively related to P treatment and cell quota from day 3-6. From day 0-3, cell quota was negatively related to P treatments at <2 μg∙L-1, but increased slightly at higher P. Cell quota decreased greatly in low P treatments from day 3-6, which may have enabled high growths in low P treatments. P uptake was positively and linearly related to P treatment during both periods. Negative uptake rates and increases in measured culture phosphorus concentrations to 5 μg∙L-1 in the lowest P treatments indicated P leaked from cells into culture medium. This leakage during early stages of the experiment may have been sufficient to stimulate metabolism and use of intracellular P stores in low P treatments for rapid growth. Our study shows P regulation of Microcystis growth can be complex as a result of changing P concentrations, and this complexity may be important for modeling Microcystis for nutrient and ecosystem management.

  9. Nitrogen saturation in stream ecosystems.

    Science.gov (United States)

    Earl, Stevan R; Valett, H Maurice; Webster, Jackson R

    2006-12-01

    The concept of nitrogen (N) saturation has organized the assessment of N loading in terrestrial ecosystems. Here we extend the concept to lotic ecosystems by coupling Michaelis-Menten kinetics and nutrient spiraling. We propose a series of saturation response types, which may be used to characterize the proximity of streams to N saturation. We conducted a series of short-term N releases using a tracer (15NO3-N) to measure uptake. Experiments were conducted in streams spanning a gradient of background N concentration. Uptake increased in four of six streams as NO3-N was incrementally elevated, indicating that these streams were not saturated. Uptake generally corresponded to Michaelis-Menten kinetics but deviated from the model in two streams where some other growth-critical factor may have been limiting. Proximity to saturation was correlated to background N concentration but was better predicted by the ratio of dissolved inorganic N (DIN) to soluble reactive phosphorus (SRP), suggesting phosphorus limitation in several high-N streams. Uptake velocity, a reflection of uptake efficiency, declined nonlinearly with increasing N amendment in all streams. At the same time, uptake velocity was highest in the low-N streams. Our conceptual model of N transport, uptake, and uptake efficiency suggests that, while streams may be active sites of N uptake on the landscape, N saturation contributes to nonlinear changes in stream N dynamics that correspond to decreased uptake efficiency.

  10. Kinetic study of enzymatic hydrolysis of potato starch

    Directory of Open Access Journals (Sweden)

    Óscar Fernando Castellanos Domínguez

    2004-01-01

    Full Text Available This article describes the kinetic study of potato starch enzymatic hydrolysis using soluble enzymes (Novo Nordisk. Different assays divided into four groups were used: reaction time (with which it was possible to reduce the 48-72 hour duration reported in the literature to 16 hours with comparable productivity levels; selecting the set of enzymes to be used (different types were evaluated - BAN and Termamyl as alfa-amylases during dextrinisation stage, and AMG, Promozyme and Fungamyl for sacarification reaction- identifying those presenting the best performance during hydrolysis.Reaction conditions were optimised for the process's two stages (destrinisation and sacarification. Enzyme dose, calcium cofactor concentration, pH, temperature and agitation speed were studied for the first stage. Enzyme ratio, pH and agitation speed were studied for sacarification; the latter parameter reported values having no antecedents in the literature (60 rpm and 30 rpm for first and second reactions, respectively. Michaelis Menten kinetics were calculated once conditions had been optimised, varying substrate from 10-50% P/V, obtaining km and Vmax kinetic parameters for each reaction. A kinetic model was found according to local working conditions which was able to explain potato starch conversion to glucose syrup, achieving 96 dextrose equivalents by the end of the reaction, being well within the maximum range reported in the literature (94-98.Laboratory equipment was constructed prior to carrying out assays which was able to reproduce and improve the conditions reported in the literature, making it a useful, reliable tool for use in assays returning good results.

  11. application of ascorbic acid 2-phosphate as a new voltammetric

    African Journals Online (AJOL)

    a

    acid 2-phosphate (AAP) as a new voltammetric substrate has been described in this paper. In the alkaline buffer .... ALP labeled goat anti-rabbit ..... Classical Michaelis-Menten kinetic experiments were carried out to measure the maximum.

  12. Influence of oxygen uptake kinetics on physical performance in youth soccer.

    Science.gov (United States)

    Doncaster, Greg; Marwood, Simon; Iga, John; Unnithan, Viswanath

    2016-09-01

    To examine the relationship between oxygen uptake kinetics (VO2 kinetics) and physical measures associated with soccer match play, within a group of highly trained youth soccer players. Seventeen highly trained youth soccer players (age: 13.3 ± 0.4 year, self-assessed Tanner stage: 3 ± 1) volunteered for the study. Players initially completed an incremental treadmill protocol to exhaustion, to establish gaseous exchange threshold (GET) and VO2max (59.1 ± 5.4 mL kg(-1) min(-1)). On subsequent visits, players completed a step transition protocol from rest-moderate-intensity exercise, followed by an immediate transition, and from moderate- to severe-intensity exercise (moderate: 95 % GET, severe: 60 %∆), during which VO2 kinetics were determined. Physical soccer-based performance was assessed using a maximal Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) and via GPS-derived measures of physical soccer performance during soccer match play, three 2 × 20 min, 11 v 11 matches, to gain measures of physical performance during soccer match play. Partial correlations revealed significant inverse relationships between the unloaded-to-moderate transition time constant (tau) and: Yo-Yo IR1 performance (r = -0.58, P = 0.02) and GPS variables [total distance (TD): r = -0.64, P = 0.007, high-speed running (HSR): r = -0.64, P = 0.008 and high-speed running efforts (HSReff): r = -0.66, P = 0.005]. Measures of VO2 kinetics are related to physical measures associated with soccer match play and could potentially be used to distinguish between those of superior physical performance, within a group of highly trained youth soccer players.

  13. Evaluation of deltamethrin kinetics and dosimetry in the maturing rat using a PBPK model

    International Nuclear Information System (INIS)

    Tornero-Velez, Rogelio; Mirfazaelian, Ahmad; Kim, Kyu-Bong; Anand, Sathanandam S.; Kim, Hyo J.; Haines, Wendy T.; Bruckner, James V.; Fisher, Jeffrey W.

    2010-01-01

    Immature rats are more susceptible than adults to the acute neurotoxicity of pyrethroid insecticides like deltamethrin (DLM). A companion kinetics study (Kim et al., in press) revealed that blood and brain levels of the neuroactive parent compound were inversely related to age in rats 10, 21, 40 and 90 days old. The objective of the current study was to modify a physiologically based pharmacokinetic (PBPK) model of DLM disposition in the adult male Sprague-Dawley rat (Mirfazaelian et al., 2006), so blood and target organ dosimetry could be accurately predicted during maturation. Age-specific organ weights and age-dependent changes in the oxidative and hydrolytic clearance of DLM were modeled with a generalized Michaelis-Menten model for growth and the summary equations incorporated into the PBPK model. The model's simulations compared favorably with empirical DLM time-courses in plasma, blood, brain and fat for the four age-groups evaluated (10, 21, 40 and 90 days old). PND 10 pups' area under the 24-h brain concentration time curve (AUC 0-24h ) was 3.8-fold higher than that of the PND 90 adults. Our maturing rat PBPK model allows for updating with age- and chemical-dependent parameters, so pyrethroid dosimetry can be forecast in young and aged individuals. Hence, this model provides a methodology for risk assessors to consider age-specific adjustments to oral Reference Doses on the basis of PK differences.

  14. Thermo-kinetics of lipase-catalyzed synthesis of 6-O-glucosyldecanoate.

    Science.gov (United States)

    Gumel, A M; Annuar, M S M; Heidelberg, T; Chisti, Y

    2011-10-01

    Lipase-catalyzed synthesis of 6-O-glucosyldecanoate from d-glucose and decanoic acid was performed in dimethyl sulfoxide (DMSO), a mixture of DMSO and tert-butanol and tert-butanol alone with a decreasing order of polarity. The highest conversion yield (> 65%) of decanoic acid was obtained in the blended solvent of intermediate polarity mainly because it could dissolve relatively large amounts of both the reactants. The reaction obeyed Michaelis-Menten type of kinetics. The affinity of the enzyme towards the limiting substrate (decanoic acid) was not affected by the polarity of the solvent, but increased significantly with temperature. The esterification reaction was endothermic with activation energy in the range of 60-67 kJ mol⁻¹. Based on the Gibbs energy values, in the solvent blend of DMSO and tert-butanol the position of the equilibrium was shifted more towards the products compared to the position in pure solvents. Monoester of glucose was the main product of the reaction. Copyright © 2011 Elsevier Ltd. All rights reserved.

  15. Rapid Determination of Enzyme Kinetics from Fluorescence: Overcoming the Inner Filter Effect

    Science.gov (United States)

    Palmier, Mark O.; Van Doren, Steven R.

    2007-01-01

    Fluorescence change is convenient for monitoring enzyme kinetics. Unfortunately, it looses linearity as the absorbance of the fluorescent substrate increases with concentration. When the sum of absorbance at excitation and emission wavelengths exceeds 0.08, this inner filtering effect (IFE) alters apparent initial velocities, Km, and kcat. The IFE distortion of apparent initial velocities can be corrected without doing fluorophore dilution assays. Using the substrate’s extinction coefficients at excitation and emission wavelengths, the inner filter effect can be modeled during curve fitting for more accurate Michaelis-Menten parameters. A faster and simpler approach is to derive kcat and Km from progress curves. Strategies to obtain reliable and reproducible estimates of kcat and Km from only two or three progress curves are illustrated using matrix metalloproteinase-12 and alkaline phosphatase. Accurate estimates of concentration of enzyme active sites and specificity constant kcat/Km (from one progress curve with [S] ≪ Km) confer accuracy, freedom of choices of [S], and robustness to kcat and Km globally fitted to a few progress curves. The economies of the progress curve approach make accurate kcat and Km more accessible from fluorescence measurements. PMID:17706587

  16. THE KINETICS OF NH(4)+ AND NO3(-) UPTAKE BY DOUGLAS-FIR FROM SINGLE N-SOLUTIONS AND FROM SOLUTIONS CONTAINING BOTH NH(4)+ AND NO3(-)

    NARCIS (Netherlands)

    KAMMINGAVANWIJK, C; PRINS, HBA

    The kinetics of NH4+ and NO3- uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the V(max) of NH4+ uptake was higher than that of NO3- uptake. The K(m) of NH4+

  17. Acute toxicity, uptake and accumulation kinetics of nickel in an invasive copepod species: Pseudodiaptomus marinus.

    Science.gov (United States)

    Tlili, Sofiène; Ovaert, Julien; Souissi, Anissa; Ouddane, Baghdad; Souissi, Sami

    2016-02-01

    Pseudodiaptomus marinus is a marine calanoid copepod originating of the Indo-Pacific region, who has successfully colonized new areas and it was recently observed in the European side of the Mediterranean Sea as well as in the North Sea. Actually, many questions were posed about the invasive capacity of this copepod in several non-native ecosystems. In this context, the main aim of this study was to investigate the tolerance and the bioaccumulation of metallic stress in the invasive copepod P. marinus successfully maintained in mass culture at laboratory conditions since 2 years. In order to study the metallic tolerance levels of P. marinus, an emergent trace metal, the nickel, was chosen. First, lethal concentrations determination experiments were done for 24, 48, 72 and 96 h in order to calculated LC50% but also to select a relevant ecological value for the suite of experiments. Then, three types of experiments, using a single concentration of nickel (correspond the 1/3 of 96 h-LC50%) was carried in order to study the toxico-kinetics of nickel in P. marinus. Concerning lethal concentrations, we observed that P. marinus was in the same range of sensitivity compared to other calanoid copepods exposed to nickel in the same standardized experimental conditions. Results showed that the uptake of nickel in P. marinus depends from the pathways of entrance (water of food), but also that Isochrysis galbana, used as a food source, has an important bioaccumulation capacity and a rapid uptake of nickel. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. A fast-start pacing strategy speeds pulmonary oxygen uptake kinetics and improves supramaximal running performance.

    Directory of Open Access Journals (Sweden)

    Tiago Turnes

    Full Text Available The focus of the present study was to investigate the effects of a fast-start pacing strategy on running performance and pulmonary oxygen uptake (VO2 kinetics at the upper boundary of the severe-intensity domain. Eleven active male participants (28±10 years, 70±5 kg, 176±6 cm, 57±4 mL/kg/min visited the laboratory for a series of tests that were performed until exhaustion: 1 an incremental test; 2 three laboratory test sessions performed at 95, 100 and 110% of the maximal aerobic speed; 3 two to four constant speed tests for the determination of the highest constant speed (HS that still allowed achieving maximal oxygen uptake; and 4 an exercise based on the HS using a higher initial speed followed by a subsequent decrease. To predict equalized performance values for the constant pace, the relationship between time and distance/speed through log-log modelling was used. When a fast-start was utilized, subjects were able to cover a greater distance in a performance of similar duration in comparison with a constant-pace performance (constant pace: 670 m±22%; fast-start: 683 m±22%; P = 0.029; subjects also demonstrated a higher exercise tolerance at a similar average speed when compared with constant-pace performance (constant pace: 114 s±30%; fast-start: 125 s±26%; P = 0.037. Moreover, the mean VO2 response time was reduced after a fast start (constant pace: 22.2 s±28%; fast-start: 19.3 s±29%; P = 0.025. In conclusion, middle-distance running performances with a duration of 2-3 min are improved and VO2 response time is faster when a fast-start is adopted.

  19. Tracer kinetics: Modelling of tracer behaviour in nonlinear and nonsteady state systems exemplified by the evaluation of protein turnover in plant organs

    International Nuclear Information System (INIS)

    Winkler, E.

    1991-01-01

    If nonlinear biological processes are investigated by means of tracer experiments they can be modelled with linear kinetic equations (compartment equations) as long as the total system is in a stationary state. But if nonstationary behaviour is included considerations on the kinetics of the individual processes are necessary. Within the range of biological and agricultural investigations especially first order reactions (constant fraction processes), zero order reactions (constant amount process) and saturation reactions (Michaelis-Menten-kinetics) are to be taken into account. A rigorous treatment of data based on system theory can be preceeded by graphic-algebraic procedure which may be more or less uncertain in its results but which can easily be handled. An example is given of methodological considerations concerning the combination of evaluation procedures and the discrimination between different reaction mechanisms. It treats protein turnover in 2 different parts of growing wheat plants investigated by means of an 15 N-tracer experiment. Whereas in a stationary system (upper stalk section) linear tracer equations were sufficient irrespective of the true reaction mechanism, for protein synthesis in the upper leaf as a nonstationary system it was necessary to decide between the hypotheses of a zero order and a first order reaction. In accordance with statements in the literature the unambiguous result was a combination of protein synthesis as a zero order process and of protein degradation as a first order process. (orig.) [de

  20. Enzymatic oxidation of rutin by horseradish peroxidase: kinetic mechanism and identification of a dimeric product by LC-Orbitrap mass spectrometry.

    Science.gov (United States)

    Savic, Sasa; Vojinovic, Katarina; Milenkovic, Sanja; Smelcerovic, Andrija; Lamshoeft, Marc; Petronijevic, Zivomir

    2013-12-15

    Flavonoid oxidation is important issue in food processing and quality. The kinetic mechanism of enzymatic oxidation of rutin by horseradish peroxidase (HRP) was studied. Rutin oxidation reaction was followed by recording of spectral changes over the time at 360 nm. The studied oxidation is mostly enzymatic and less part non-enzymatic. The reaction with HRP has a higher rate compared with the reaction without of HRP, whereby is part of non-enzymatic reaction about 10% of the total reaction. Kinetic parameters were determined from graphics of linear Michaelis-Menten equation, and it was found that investigated reactions of rutin oxidation by HRP take place in a ping-pong kinetic mechanism. High resolution HPLC-MS analysis of the mixture of oxidized products of rutin revealed the presence of rutin dimer. Because of widely distribution of rutin as well as presence of peroxidases and hydrogen peroxide in fresh foods identification of this enzymatic modification product can be beneficial for foods quality and safety. Copyright © 2013 Elsevier Ltd. All rights reserved.

  1. OXYGEN UPTAKE KINETICS DURING INCREMENTAL- AND DECREMENTAL-RAMP CYCLE ERGOMETRY

    Directory of Open Access Journals (Sweden)

    Fadıl Özyener

    2011-09-01

    Full Text Available The pulmonary oxygen uptake (VO2 response to incremental-ramp cycle ergometry typically demonstrates lagged-linear first-order kinetics with a slope of ~10-11 ml·min-1·W-1, both above and below the lactate threshold (ӨL, i.e. there is no discernible VO2 slow component (or "excess" VO2 above ӨL. We were interested in determining whether a reverse ramp profile would yield the same response dynamics. Ten healthy males performed a maximum incremental -ramp (15-30 W·min-1, depending on fitness. On another day, the work rate (WR was increased abruptly to the incremental maximum and then decremented at the same rate of 15-30 W.min-1 (step-decremental ramp. Five subjects also performed a sub-maximal ramp-decremental test from 90% of ӨL. VO2 was determined breath-by-breath from continuous monitoring of respired volumes (turbine and gas concentrations (mass spectrometer. The incremental-ramp VO2-WR slope was 10.3 ± 0.7 ml·min-1·W-1, whereas that of the descending limb of the decremental ramp was 14.2 ± 1.1 ml·min-1·W-1 (p < 0.005. The sub-maximal decremental-ramp slope, however, was only 9. 8 ± 0.9 ml·min-1·W-1: not significantly different from that of the incremental-ramp. This suggests that the VO2 response in the supra-ӨL domain of incremental-ramp exercise manifest not actual, but pseudo, first-order kinetics

  2. Steady-state cerebral glucose concentrations and transport in the human brain

    OpenAIRE

    Gruetter, R.; Ugurbil, K.; Seaquist, E. R.

    1998-01-01

    Understanding the mechanism of brain glucose transport across the blood- brain barrier is of importance to understanding brain energy metabolism. The specific kinetics of glucose transport nave been generally described using standard Michaelis-Menten kinetics. These models predict that the steady- state glucose concentration approaches an upper limit in the human brain when the plasma glucose level is well above the Michaelis-Menten constant for half-maximal transport, K(t). In experiments wh...

  3. A unified approach to model uptake kinetics of trace elements in complex aqueous – solid solution systems

    International Nuclear Information System (INIS)

    Thien, Bruno M.J.; Kulik, Dmitrii A.; Curti, Enzo

    2014-01-01

    Highlights: • There are several models able to describe trace element partitioning in growing minerals. • To describe complex systems, those models must be embedded in a geochemical code. • We merged two models into a unified one suitable for implementation in a geochemical code. • This unified model was tested against coprecipitation experimental data. • We explored how our model reacts to solution depletion effects. - Abstract: Thermodynamics alone is usually not sufficient to predict growth-rate dependencies of trace element partitioning into host mineral solid solutions. In this contribution, two uptake kinetic models were analyzed that are promising in terms of mechanistic understanding and potential for implementation in geochemical modelling codes. The growth Surface Entrapment Model (Watson, 2004) and the Surface Reaction Kinetic Model (DePaolo, 2011) were shown to be complementary, and under certain assumptions merged into a single analytical expression. This Unified Uptake Kinetics Model was implemented in GEMS3K and GEM-Selektor codes ( (http://gems.web.psi.ch)), a Gibbs energy minimization package for geochemical modelling. This implementation extends the applicability of the unified uptake kinetics model to accounting for non-trivial factors influencing the trace element partitioning into solid solutions, such as the changes in aqueous solution composition and speciation, or the depletion effects in closed geochemical systems

  4. Heart Rate and Oxygen Uptake Kinetics in Type 2 Diabetes Patients - A Pilot Study on the Influence of Cardiovascular Medication on Regulatory Processes.

    Science.gov (United States)

    Koschate, Jessica; Drescher, Uwe; Baum, Klaus; Brinkmann, Christian; Schiffer, Thorsten; Latsch, Joachim; Brixius, Klara; Hoffmann, Uwe

    2017-05-01

    The aim of this pilot study was to investigate whether there are differences in heart rate and oxygen uptake kinetics in type 2 diabetes patients, considering their cardiovascular medication. It was hypothesized that cardiovascular medication would affect heart rate and oxygen uptake kinetics and that this could be detected using a standardized exercise test. 18 subjects were tested for maximal oxygen uptake. Kinetics were measured in a single test session with standardized, randomized moderate-intensity work rate changes. Time series analysis was used to estimate kinetics. Greater maxima in cross-correlation functions indicate faster kinetics. 6 patients did not take any cardiovascular medication, 6 subjects took peripherally acting medication and 6 patients were treated with centrally acting medication. Maximum oxygen uptake was not significantly different between groups. Significant main effects were identified regarding differences in muscular oxygen uptake kinetics and heart rate kinetics. Muscular oxygen uptake kinetics were significantly faster than heart rate kinetics in the group with no cardiovascular medication (maximum in cross-correlation function of muscular oxygen uptake vs. heart rate; 0.32±0.08 vs. 0.25±0.06; p=0.001) and in the group taking peripherally acting medication (0.34±0.05 vs. 0.28±0.05; p=0.009) but not in the patients taking centrally acting medication (0.28±0.05 vs. 0.30±0.07; n.s.). It can be concluded that regulatory processes for the achievement of a similar maximal oxygen uptake are different between the groups. The used standardized test provided plausible results for heart rate and oxygen uptake kinetics in a single measurement session in this patient group. © Georg Thieme Verlag KG Stuttgart · New York.

  5. Kinetics of cellular uptake of viruses and nanoparticles via clathrin-mediated endocytosis

    Science.gov (United States)

    Banerjee, Anand; Berezhkovskii, Alexander; Nossal, Ralph

    2016-02-01

    Several viruses exploit clathrin-mediated endocytosis to gain entry into host cells. This process is also used extensively in biomedical applications to deliver nanoparticles (NPs) to diseased cells. The internalization of these nano-objects is controlled by the assembly of a clathrin-containing protein coat on the cytoplasmic side of the plasma membrane, which drives the invagination of the membrane and the formation of a cargo-containing endocytic vesicle. Current theoretical models of receptor-mediated endocytosis of viruses and NPs do not explicitly take coat assembly into consideration. In this paper we study cellular uptake of viruses and NPs with a focus on coat assembly. We characterize the internalization process by the mean time between the binding of a particle to the membrane and its entry into the cell. Using a coarse-grained model which maps the stochastic dynamics of coat formation onto a one-dimensional random walk, we derive an analytical formula for this quantity. A study of the dependence of the mean internalization time on NP size shows that there is an upper bound above which this time becomes extremely large, and an optimal size at which it attains a minimum. Our estimates of these sizes compare well with experimental data. We also study the sensitivity of the obtained results on coat parameters to identify factors which significantly affect the internalization kinetics.

  6. Kinetic Analysis of the Uptake and Release of Fluorescein by Metal-Organic Framework Nanoparticles

    Directory of Open Access Journals (Sweden)

    Tobias Preiß

    2017-02-01

    Full Text Available Metal-organic framework nanoparticles (MOF NPs are promising guest-host materials with applications in separation, storage, catalysis, and drug delivery. However, on- and off-loading of guest molecules by porous MOF nanostructures are still poorly understood. Here we study uptake and release of fluorescein by two representative MOF NPs, MIL-100(Fe and MIL-101(Cr. Suspensions of these MOF NPs exhibit well-defined size distributions and crystallinity, as verified by electron microscopy, dynamic light scattering, and X-ray diffraction. Using absorbance spectroscopy the equilibrium dissociation constants and maximum numbers of adsorbed fluorescein molecules per NP were determined. Time-resolved fluorescence studies reveal that rates of release and loading are pH dependent. The kinetics observed are compared to theoretical estimates that account for bulk diffusion into NPs, and retarded internal diffusion and adsorption rates. Our study shows that, rather than being simple volumetric carriers, MOF-NPs are dominated by internal surface properties. The findings will help to optimize payload levels and develop release strategies that exploit varying pH for drug delivery.

  7. Kinetics of pyrophosphate-driven proton uptake by acidocalcisomes of Leptomonas wallacei

    International Nuclear Information System (INIS)

    Moraes Moreira, Bernardo Luiz; Soares Medeiros, Lia Carolina A.; Miranda, Kildare; Souza, Wanderley de; Hentschel, Joachim; Plattner, Helmut; Barrabin, Hector

    2005-01-01

    In this work, we show the kinetics of pyrophosphate-driven H + uptake by acidocalcisomes in digitonin-permeabilized promastigotes of Leptomonas wallacei. The vacuolar proton pyrophosphatase activity was optimal in the pH range of 7.5-8.0, was inhibited by imidiodiphosphate, and was completely dependent on K + and PPi. H + was released with the addition of Ca 2+ , suggesting the presence of a Ca 2+ /H + antiport. In addition, X-ray elemental mapping associated with energy-filtering transmission electron microscopy showed that most of the Ca, Na, Mg, P, K, Fe, and Zn were located in acidocalcisomes. L. wallacei immunolabeled with antibodies against Trypanosoma cruzi pyrophosphatase show intense fluorescence in cytoplasmatic organelles of size and distribution similar to the acidocalcisomes. Altogether, the results show that L. wallacei acidocalcisomes possess a H + -pyrophosphatase with characteristics of type I V-H + -PPase. However, we did not find any evidence, either for the presence of H + -ATPases or for Na + /H + exchangers in these acidocalcisomes

  8. Influence of exercise intensity on skeletal muscle blood flow, O2 extraction and O2 uptake on-kinetics

    Science.gov (United States)

    Jones, Andrew M; Krustrup, Peter; Wilkerson, Daryl P; Berger, Nicolas J; Calbet, José A; Bangsbo, Jens

    2012-01-01

    Following the start of low-intensity exercise in healthy humans, it has been established that the kinetics of skeletal muscle O2 delivery is faster than, and does not limit, the kinetics of muscle O2 uptake (). Direct data are lacking, however, on the question of whether O2 delivery might limit kinetics during high-intensity exercise. Using multiple exercise transitions to enhance confidence in parameter estimation, we therefore investigated the kinetics of, and inter-relationships between, muscle blood flow (), a– difference and following the onset of low-intensity (LI) and high-intensity (HI) exercise. Seven healthy males completed four 6 min bouts of LI and four 6 min bouts of HI single-legged knee-extension exercise. Blood was frequently drawn from the femoral artery and vein during exercise and , a– difference and were calculated and subsequently modelled using non-linear regression techniques. For LI, the fundamental component mean response time (MRTp) for kinetics was significantly shorter than kinetics (mean ± SEM, 18 ± 4 vs. 30 ± 4 s; P exercise intensities; however, the MRTp for a– difference was significantly shorter for HI compared with LI (17 ± 3 vs. 28 ± 4 s; P exercise and remained unaltered thereafter, with no differences between LI and HI. These results indicate that bulk O2 delivery does not limit kinetics following the onset of LI or HI knee-extension exercise. PMID:22711961

  9. In vivo measurements of brain glucose transport using the reversible michaelis-menten model and simultaneous measurements of cerebral blood flow changes during hypoglycemia

    OpenAIRE

    Choi, I.-Y.; Lee, S.-P.; Kim, S.-G.; Gruetter, R.

    2001-01-01

    Glucose is the major substrate that sustains normal brain function. When the brain glucose concentration approaches zero, glucose transport across the blood-brain barrier becomes rate limiting for metabolism during, for example, increased metabolic activity and hypoglycemia. Steady-state brain glucose concentrations in α-chloralose anesthetized rats were measured noninvasively as a function of plasma glucose. The relation between brain and plasma glucose was linear at 4.5 to 30 mmol/L plasma ...

  10. At the centennial of Michaelis and Menten, competing Michaelis-Menten steps explain effect of GLP-1 on blood-brain transfer and metabolism of glucose

    DEFF Research Database (Denmark)

    Jensen, Michael Gejl; Rungby, Jørgen; Brock, Birgitte

    2014-01-01

    Glucagon-like peptide-1 (GLP-1) is a potent insulinotropic incretin hormone with pancreatic and extrapancreatic effects. Studies reveal significant effects in regions of brain tissue that regulate appetite and satiety. The effects cause that mimetics of GLP-1 serves as treatment of type 2 diabete...

  11. The influence of different space-related physiological variations on exercise capacity determined by oxygen uptake kinetics

    Science.gov (United States)

    Stegemann, J.

    Oxygen uptake kinetics, following defined variations of work load changes allow to estimate the contribution of aerob and anaerob energy supply which is the base for determining work capacity. Under the aspect of long duration missions with application of adequate dosed countermeasures, a reliable estimate of the astronaut's work capacity is important to adjust the necessary inflight training. Since the kinetics of oxygen uptake originate in the working muscle group itself, while measurements are performed at the mouth, various influences within the oxygen transport system might disturb the determinations. There are not only detraining effects but also well-known other influences, such as blood- and fluid shifts induced by weightlessness. They might have an impact on the circulatory system. Some of these factors have been simulated by immersion, blood donation, and changing of the body position.

  12. Generic Schemes for Single-Molecule Kinetics. 3: Self-Consistent Pathway Solutions for Nonrenewal Processes.

    Science.gov (United States)

    Piephoff, D Evan; Cao, Jianshu

    2018-04-23

    We recently developed a pathway analysis framework (paper 1) for describing single-molecule kinetics for renewal (i.e., memoryless) processes based on the decomposition of a kinetic scheme into generic structures. In our approach, waiting time distribution functions corresponding to such structures are expressed in terms of self-consistent pathway solutions and concatenated to form measurable probability distribution functions (PDFs), affording a simple way to decompose and recombine a network. Here, we extend this framework to nonrenewal processes, which involve correlations between events, and employ it to formulate waiting time PDFs, including the first-passage time PDF, for a general kinetic network model. Our technique does not require the assumption of Poissonian kinetics, permitting a more general kinetic description than the usual rate approach, with minimal topological restrictiveness. To demonstrate the usefulness of this technique, we provide explicit calculations for our general model, which we adapt to two generic schemes for single-enzyme turnover with conformational interconversion. For each generic scheme, wherein the intermediate state(s) need not undergo Poissonian decay, the functional dependence of the mean first-passage time on the concentration of an external substrate is analyzed. When conformational detailed balance is satisfied, the enzyme turnover rate (related to the mean first-passage time) reduces to the celebrated Michaelis-Menten functional form, consistent with our previous work involving a similar scheme with all rate processes, thereby establishing further generality to this intriguing result. Our framework affords a general and intuitive approach for evaluating measurable waiting time PDFs and their moments, making it a potentially useful kinetic tool for a wide variety of single-molecule processes.

  13. Characterization of simvastatin acid uptake by organic anion transporting polypeptide 3A1 (OATP3A1) and influence of drug-drug interaction.

    Science.gov (United States)

    Atilano-Roque, Amandla; Joy, Melanie S

    2017-12-01

    Human organic anion transporting polypeptide 3A1 (OATP3A1) is predominately expressed in the heart. The ability of OATP3A1 to transport statins into cardiomyocytes is unknown, although other OATPs are known to mediate the uptake of statin drugs in liver. The pleiotropic effects and uptake of simvastatin acid were analyzed in primary human cardiomyocytes and HEK293 cells transfected with the OATP3A1 gene. Treatment with simvastatin acid reduced indoxyl sulfate-mediated reactive oxygen species and modulated OATP3A1 expression in cardiomyocytes and HEK293 cells transfected with the OATP3A1 gene. We observed a pH-dependent effect on OATP3A1 uptake, with more efficient simvastatin acid uptake at pH5.5 in HEK293 cells transfected with the OATP3A1 gene. The Michaelis-Menten constant (K m ) for simvastatin acid uptake by OATP3A1 was 0.017±0.002μM and the V max was 0.995±0.027fmol/min/10 5 cells. Uptake of simvastatin acid was significantly increased by known (benzylpenicillin and estrone-3-sulfate) and potential (indoxyl sulfate and cyclosporine) substrates of OATP3A1. In conclusion, the presence of OATP3A1 in cardiomyocytes suggests that this transporter may modulate the exposure of cardiac tissue to simvastatin acid due to its enrichment in cardiomyocytes. Increases in uptake of simvastatin acid by OATP3A1 when combined with OATP substrates suggest the potential for drug-drug interactions that could influence clinical outcomes. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. The mechanism distinguishability problem in biochemical kinetics: the single-enzyme, single-substrate reaction as a case study.

    Science.gov (United States)

    Schnell, Santiago; Chappell, Michael J; Evans, Neil D; Roussel, Marc R

    2006-01-01

    A theoretical analysis of the distinguishability problem of two rival models of the single enzyme-single substrate reaction, the Michaelis-Menten and Henri mechanisms, is presented. We also outline a general approach for analysing the structural indistinguishability between two mechanisms. The approach involves constructing, if possible, a smooth mapping between the two candidate models. Evans et al. [N.D. Evans, M.J. Chappell, M.J. Chapman, K.R. Godfrey, Structural indistinguishability between uncontrolled (autonomous) nonlinear analytic systems, Automatica 40 (2004) 1947-1953] have shown that if, in addition, either of the mechanisms satisfies a particular criterion then such a transformation always exists when the models are indistinguishable from their experimentally observable outputs. The approach is applied to the single enzyme-single substrate reaction mechanism. In principle, mechanisms can be distinguished using this analysis, but we show that our ability to distinguish mechanistic models depends both on the precise measurements made, and on our knowledge of the system prior to performing the kinetics experiments.

  15. Kinetics of the removal of mono-chlorobenzene vapour from waste gases using a trickle bed air biofilter.

    Science.gov (United States)

    Mathur, Anil K; Sundaramurthy, J; Balomajumder, C

    2006-10-11

    The performance of a trickle bed air biofilter (TBAB) in the removal of mono-chlorobenzene (MCB) was evaluated in concentrations varying from 0.133 to 7.187 g m(-3) and at empty bed residence time (EBRT) varying from 37.7 to 188.52 s. More than 90% removal efficiency in the trickle bed air biofilter was achieved for the inlet MCB concentration up to 1.069 g m(-3) and EBRT less than 94.26 s. The trickle bed air biofilter was constructed with coal packing material, inoculated with a mixed consortium of activated sludge obtained from sewage treatment plant. The continuous performance of the removal of MCB in the trickle bed air biofilter was monitored for various gas concentrations, gas flow rates, and empty bed residence time. The experiment was conducted for a period of 75 days. The trickle bed air biofilter degrading MCB with an average elimination capacity of 80 g m(-3) h(-1) was obtained. The effect of starvation was also studied. After starvation period of 8 days, the degradation was low but recovered within a short period of time. Using macrokinetic determination method, the Michaelis-Menten kinetic constant K(m) and maximum reaction rate, r(max) evaluated as 0.121 g m(-3) s(-1) and 7.45 g m(-3), respectively.

  16. The Non-Linear Child: Ontogeny, Isoniazid Concentration, and NAT2 Genotype Modulate Enzyme Reaction Kinetics and Metabolism.

    Science.gov (United States)

    Rogers, Zoe; Hiruy, Hiwot; Pasipanodya, Jotam G; Mbowane, Chris; Adamson, John; Ngotho, Lihle; Karim, Farina; Jeena, Prakash; Bishai, William; Gumbo, Tawanda

    2016-09-01

    N-acetyltransferase 2 (NAT2) catalyzes the acetylation of isoniazid to N-acetylisoniazid. NAT2 polymorphism explains 88% of isoniazid clearance variability in adults. We examined the effects of clinical and genetic factors on Michaelis-Menten reaction kinetic constants of maximum velocity (V max ) and affinity (K m ) in children 0-10years old. We measured the rates of isoniazid elimination and N-acetylisoniazid production in the blood of 30 children. Since maturation effects could be non-linear, we utilized a pharmacometric approach and the artificial intelligence method, multivariate adaptive regression splines (MARS), to identify factors predicting NAT2 V max and K m by examining clinical, genetic, and laboratory factors in toto. Isoniazid concentration predicted both V max and K m and superseded the contribution of NAT2 genotype. Age non-linearly modified the NAT2 genotype contribution until maturation at ≥5.3years. Thus, enzyme efficiency was constrained by substrate concentration, genes, and age. Since MARS output is in the form of basis functions and equations, it allows multiscale systems modeling from the level of cellular chemical reactions to whole body physiological parameters, by automatic selection of significant predictors by the algorithm. Copyright © 2016 Forschungsgesellschaft für Arbeitsphysiologie und Arbeitschutz e.V. Published by Elsevier B.V. All rights reserved.

  17. The Non-Linear Child: Ontogeny, Isoniazid Concentration, and NAT2 Genotype Modulate Enzyme Reaction Kinetics and Metabolism

    Directory of Open Access Journals (Sweden)

    Zoe Rogers

    2016-09-01

    Full Text Available N-acetyltransferase 2 (NAT2 catalyzes the acetylation of isoniazid to N-acetylisoniazid. NAT2 polymorphism explains 88% of isoniazid clearance variability in adults. We examined the effects of clinical and genetic factors on Michaelis-Menten reaction kinetic constants of maximum velocity (Vmax and affinity (Km in children 0–10 years old. We measured the rates of isoniazid elimination and N-acetylisoniazid production in the blood of 30 children. Since maturation effects could be non-linear, we utilized a pharmacometric approach and the artificial intelligence method, multivariate adaptive regression splines (MARS, to identify factors predicting NAT2 Vmax and Km by examining clinical, genetic, and laboratory factors in toto. Isoniazid concentration predicted both Vmax and Km and superseded the contribution of NAT2 genotype. Age non-linearly modified the NAT2 genotype contribution until maturation at ≥5.3 years. Thus, enzyme efficiency was constrained by substrate concentration, genes, and age. Since MARS output is in the form of basis functions and equations, it allows multiscale systems modeling from the level of cellular chemical reactions to whole body physiological parameters, by automatic selection of significant predictors by the algorithm.

  18. Evaluation of sources of variation on in vitro fermentation kinetics of feedstuffs in a gas production system.

    Science.gov (United States)

    Keim, Juan P; Alvarado-Gilis, Christian; Arias, Rodrigo A; Gandarillas, Mónica; Cabanilla, Jaime

    2017-10-01

    The aim of this study was to evaluate the effect of different sources of variation in gas production technique on the in vitro gas production kinetics of feedstuffs. Triplicates of commercial concentrate, grass silage, grass hay and grass pasture were incubated in three experiments: experiment 1 assessed two agitation methods; experiment 2 evaluated different rumen inocula (pooled or different donor cows for each incubation run); and experiment 3 used Goering-Van Soest or Mould buffers for media preparation. Gas production data were fitted into the Michaelis-Menten model and then subjected to analysis of variance. Gas production (GP) at 48 h and asymptote gas production (A) were lower when bottles were continuously under horizontal movement. Time to produce half and 75% of A, and A were affected by rumen inocula, while buffer type affected time to produce half and 25% of A and GP. No interactions between substrates and sources of variation were observed, suggesting that the effects of substrates on GP parameters were not modified. It is concluded that comparison of numerical data from in vitro experiments that follow different protocols must be done carefully. However, the ranking of different substrates is more robust and less affected by the sources of variation. © 2017 Japanese Society of Animal Science.

  19. Effects of Iron-Oxide Nanoparticle Surface Chemistry on Uptake Kinetics and Cytotoxicity in CHO-K1 Cells

    Directory of Open Access Journals (Sweden)

    Camille C. Hanot

    2015-12-01

    Full Text Available Superparamagnetic iron-oxide nanoparticles (SPIONs show great promise for multiple applications in biomedicine. While a number of studies have examined their safety profile, the toxicity of these particles on reproductive organs remains uncertain. The goal of this study was to evaluate the cytotoxicity of starch-coated, aminated, and PEGylated SPIONs on a cell line derived from Chinese Hamster ovaries (CHO-K1 cells. We evaluated the effect of particle diameter (50 and 100 nm and polyethylene glycol (PEG chain length (2k, 5k and 20k Da on the cytotoxicity of SPIONs by investigating cell viability using the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT and sulforhodamine B (SRB assays. The kinetics and extent of SPION uptake by CHO-K1 cells was also studied, as well as the resulting generation of intracellular reactive oxygen species (ROS. Cell toxicity profiles of SPIONs correlated strongly with their cellular uptake kinetics, which was strongly dependent on surface properties of the particles. PEGylation caused a decrease in both uptake and cytotoxicity compared to aminated SPIONs. Interestingly, 2k Da PEG-modifed SPIONs displayed the lowest cellular uptake and cytotoxicity among all studied particles. These results emphasize the importance of surface coatings when engineering nanoparticles for biomedical applications.

  20. Root-exuded acid phosphatase and 32Pi-uptake kinetics of wheat, rye and triticale under phosphorus starvation

    International Nuclear Information System (INIS)

    Pandey, Renu

    2006-01-01

    A nutrient culture experiment was conducted with cereal species viz., wheat (Triticum aestivum L.) cv. PBW-343), rye (Secale cereale L cv. R-308) and triticale (Triticale octoploide L. cv. DT-46), a hybrid of wheat and rye, to examine the genetic variation in root-exuded acid phosphatase (ACPase) activity and kinetics of 32 Pi-uptake under P deficient condition. The ACPase activity was assayed in the extract (intra-) and on surface (extra-cellular) or root, using p-nitrophenyl phosphate as substrate. Significantly higher ACPase activity was observed in wheat followed by rye and triticale both on the root surface and in root extract. In general, root surface ACPase activity was 2.2-fold higher than that in root extract. A strong correlation (r 2 = 0.87**) between extra and intra-cellular ACPase activity was observed. In terms of kinetic parameters, it was observed that 32 Pi uptake and I max values were significantly higher in rye while C min and K m were lowest compared to wheat and triticale. The dry weights of shoot, root and total plant were significantly higher in rye compared to wheat and triticale. Rye also had higher amount of total plant P content The superiority of rye over wheat and triticale in P uptake was observed mainly due to efficient Pi-uptake system, which needs further studies to ascertain the enhancement of Pi-induced high-affinity P transporter in these cereals. (author)

  1. Artifacts in measuring aerosol uptake kinetics: the roles of time, concentration and adsorption

    Directory of Open Access Journals (Sweden)

    L. H. Renbaum

    2011-07-01

    Full Text Available In laboratory studies of organic aerosol particles reacting with gas-phase oxidants, high concentrations of radicals are often used to study on the timescale of seconds reactions which may be occurring over days or weeks in the troposphere. Implicit in this approach is the assumption that radical concentration and time are interchangeable parameters, though this has not been established. Here, the kinetics of OH- and Cl-initiated oxidation reactions of model single-component liquid (squalane and supercooled (brassidic acid and 2-octyldodecanoic acid organic aerosols are studied by varying separately the radical concentration and the reaction time. Two separate flow tubes with residence times of 2 and 66 s are used, and [OH] and [Cl] are varied by adjusting either the laser photolysis fluence or the radical precursor concentration ([O3] or [Cl2], respectively used to generate the radicals. It is found that the rates measured by varying the radical concentration and the reaction time are equal only if the precursor concentrations are the same in the two approaches. Further, the rates depend on the concentrations of the precursor species with a Langmuir-type functional form suggesting that O3 and Cl2 saturate the surface of the liquid particles. It is believed that the presence of O3 inhibits the rate of OH reaction, perhaps by reacting with OH radicals or by O3 or intermediate species blocking surface sites, while Cl2 enhances the rate of Cl reaction by participating in a radical chain mechanism. These results have important implications for laboratory experiments in which high concentrations of gas-phase oxidants are used to study atmospheric reactions over short timescales and may explain the variability in recent measurements of the reactive uptake of OH on squalane particles in reactor systems used in this and other laboratories.

  2. The kinetics of phagocytosis of 198Au colloids ''in vitro''

    International Nuclear Information System (INIS)

    Astorri, N.L.; Bergoc, R.M.; Bianchin, A.M.; Caro, R.A.; Ihlo, J.E.; Rivera, E.S.

    1982-01-01

    The kinetics of the phagocytosis of 198-Au colloids by macrophages ''in vitro'' was studied by incubating during 5 hours phagocytic cells from the liver and the spleen of Wistar rats with colloidal radiogold particles, in the presence of an adequate culture medium (TC-199 with 10 per cent of Bovine Fetal Serum). In each experiment, the number of colloidal gold particles offered to each phatocytic cell, (Au) 0 and the mean rate of phagocytosis v, were calculated. The latter value was determined by measuring the radioactivity incorporated into the phagocytic cells during the incubation; it was expressed as the number of phagocytized colloidal gold particles per cell per minute. The values of log v = f [log (Au) 0 ] were plotted. The Lineweaver-Burk analysis of the results demonstrates that the kinetics of the phagocytosis of colloidal radiogold particles ''in vitro'' follows a model similar to Michaelis-Menten equations for enzyme reactions. The values of the substratum constant Ks and maximun velocity Vm were obtained by the regression analysis of the 1/v vs. 1/(Au) 0 graph. Vm was equal to 9.44 x 10 and 1.63 x 10 phagocytized colloidal gold particles per cell per minute for liver and spleen macrophages, respectively. Ks was equal to 6.01 x 10 9 and 8.02 x 10 8 colloidal gold particles per cell for liver and spleen macrophages, respectively. The significance of these differences is discussed and attributed mainly to a change of the specific engulfment rate constant. (author) [es

  3. Relative contributions of copper oxide nanoparticles and dissolved copper to Cu uptake kinetics of Gulf killifish (Fundulus grandis) embryos

    Science.gov (United States)

    Jiang, Chuanjia; Castellon, Benjamin T.; Matson, Cole W.; Aiken, George R.; Hsu-Kim, Heileen

    2017-01-01

    The toxicity of soluble metal-based nanomaterials may be due to the uptake of metals in both dissolved and nanoparticulate forms, but the relative contributions of these different forms to overall metal uptake rates under environmental conditions are not quantitatively defined. Here, we investigated the linkage between the dissolution rates of copper(II) oxide (CuO) nanoparticles (NPs) and their bioavailability to Gulf killifish (Fundulus grandis) embryos, with the aim of quantitatively delineating the relative contributions of nanoparticulate and dissolved species for Cu uptake. Gulf killifish embryos were exposed to dissolved Cu and CuO NP mixtures comprising a range of pH values (6.3–7.5) and three types of natural organic matter (NOM) isolates at various concentrations (0.1–10 mg-C L–1), resulting in a wide range of CuO NP dissolution rates that subsequently influenced Cu uptake. First-order dissolution rate constants of CuO NPs increased with increasing NOM concentration and for NOM isolates with higher aromaticity, as indicated by specific ultraviolet absorbance (SUVA), while Cu uptake rate constants of both dissolved Cu and CuO NP decreased with NOM concentration and aromaticity. As a result, the relative contribution of dissolved Cu and nanoparticulate CuO species for the overall Cu uptake rate was insensitive to NOM type or concentration but largely determined by the percentage of CuO that dissolved. These findings highlight SUVA and aromaticity as key NOM properties affecting the dissolution kinetics and bioavailability of soluble metal-based nanomaterials in organic-rich waters. These properties could be used in the incorporation of dissolution kinetics into predictive models for environmental risks of nanomaterials.

  4. Chromium and zinc uptake by algae Gelidium and agar extraction algal waste: kinetics and equilibrium.

    Science.gov (United States)

    Vilar, Vítor J P; Botelho, Cidália M S; Boaventura, Rui A R

    2007-11-19

    Biosorption of chromium and zinc ions by an industrial algal waste, from agar extraction industry has been studied in a batch system. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction, and the industrial waste immobilized with polyacrylonitrile (composite material). Langmuir and Langmuir-Freundlich equilibrium models describe well the equilibrium data. The parameters of Langmuir equilibrium model at pH 5.3 and 20 degrees C were for the algae, q(L)=18 mg Cr(III)g(-1) and 13 mgZn(II)g(-1), K(L) = 0.021l mg(-1)Cr(III) and 0.026l mg(-1) Zn(II); for the algal waste, q(L)=12 mgCr(III)g(-1) and 7mgZn(II)g(-1), K(L)=0.033lmg(-1) Cr(III) and 0.042l mg(-1) Zn(II); for the composite material, q(L) = 9 mgCr(III)g(-1) and 6 mgZn(II)g(-1), K(L)=0.032l mg(-1)Cr(III) and 0.034l mg(-1)Zn(II). The biosorbents exhibited a higher preference for Cr(III) ions and algae Gelidium is the best one. The pseudo-first-order Lagergren and pseudo-second-order models fitted well the kinetic data for the two metal ions. Kinetic constants and equilibrium uptake concentrations given by the pseudo-second-order model for an initial Cr(III) and Zn(II) concentration of approximately 100 mgl(-1), at pH 5.3 and 20 degrees C were k(2,ads)=0.04 g mg(-1)Cr(III)min(-1) and 0.07 g mg(-1)Zn(II)min(-1), q(eq)=11.9 mgCr(III)g(-1) and 9.5 mgZn(II)g(-1) for algae; k(2,ads)=0.17 g mg(-1)Cr(III)min(-1) and 0.19 g mg(-1)Zn(II)min(-1), q(eq)=8.3 mgCr(III)g(-1) and 5.6 mgZn(II)g(-1) for algal waste; k(2,ads)=0.01 g mg(-1)Cr(III)min(-1) and 0.18 g mg(-1)Zn(II)min(-1), q(eq)=8.0 mgCr(III)g(-1) and 4.4 mgZn(II)g(-1) for composite material. Biosorption was modelled using a batch adsorber mass transfer kinetic model, which successfully predicts Cr(III) and Zn(II) concentration profiles. The calculated average homogeneous diffusivities, D(h), were 4.2 x 10(-8), 8.3 x 10(-8) and 1.4 x 10(-8)cm(2)s(-1) for Cr(III) and 4.8 x 10(-8), 9.7 x 10(-8) and 6.2 x 10(-8)cm(2)s(-1

  5. Effects of oxygen delivery, dietary nitrate, intensified training and prior exercise on oxygen uptake kinetics and performance in humans

    DEFF Research Database (Denmark)

    Christensen, Peter Møller

    benefits from supplementing with nitrate to improve exercise efficiency and performance in endurance trained subjects. Furthermore it appears difficult to improve VO2 kinetics with intensified training in trained athletes; however intense exercise can amplify the VO2 response during subsequent high......In response to an increase in the metabolic demand the oxygen uptake (VO2) increases in an exponential fashion in exercising muscles and stabilizes after 1-2 min eventually reaching a plateau or steady state where the energy demand is matched by the l vel of VO2. VO2 kinetics describes the distinct...... phases of the VO2 response at the onset of exercise. Fast VO2 kinetics are considered to be beneficial in intense endurance sports with competitions lasting ~2-8 min, whereas low VO2 at steady state (high efficiency) is considered beneficial especially in events of longer duration. To improve...

  6. Use of an uncertainty analysis for genome-scale models as a prediction tool for microbial growth processes in subsurface environments.

    Science.gov (United States)

    Klier, Christine

    2012-03-06

    The integration of genome-scale, constraint-based models of microbial cell function into simulations of contaminant transport and fate in complex groundwater systems is a promising approach to help characterize the metabolic activities of microorganisms in natural environments. In constraint-based modeling, the specific uptake flux rates of external metabolites are usually determined by Michaelis-Menten kinetic theory. However, extensive data sets based on experimentally measured values are not always available. In this study, a genome-scale model of Pseudomonas putida was used to study the key issue of uncertainty arising from the parametrization of the influx of two growth-limiting substrates: oxygen and toluene. The results showed that simulated growth rates are highly sensitive to substrate affinity constants and that uncertainties in specific substrate uptake rates have a significant influence on the variability of simulated microbial growth. Michaelis-Menten kinetic theory does not, therefore, seem to be appropriate for descriptions of substrate uptake processes in the genome-scale model of P. putida. Microbial growth rates of P. putida in subsurface environments can only be accurately predicted if the processes of complex substrate transport and microbial uptake regulation are sufficiently understood in natural environments and if data-driven uptake flux constraints can be applied.

  7. Physiological background of the change point in VO2 and the slow component of oxygen uptake kinetics.

    Science.gov (United States)

    Zoładź, J A; Korzeniewski, B

    2001-06-01

    It is generally believed that oxygen uptake during incremental exercise--until VO2max, increases linearly with power output (see eg. Astrand & Rodahl, 1986). On the other hand, it is well established that the oxygen uptake reaches a steady state only during a low power output exercise, but during a high power output exercise, performed above the lactate threshold (LT), the oxygen uptake shows a continuous increase until the end of the exercise. This effect has been called the slow component of VO2 kinetics (Whipp & Wasserman, 1972). The presence of a slow component in VO2 kinetics implies that during an incremental exercise test, after the LT has been exceeded, the VO2 to power output relationship has to become curvilinear. Indeed, it has recently been shown that during the incremental exercise, the exceeding of the power output, at which blood lactate begins to accumulate (LT), causes a non-proportional increase in VO2 (Zoladz et al. 1995) which indicates a drop in muscle mechanical efficiency. The power output at which VO2 starts to rise non-proportionally to the power output has been called "the change point in VO2" (Zoladz et al. 1998). In this paper, the significance of the factors most likely involved in the physiological mechanism responsible for the change point in oxygen uptake (CP-VO2) and for the slow component of VO2 kinetics, including: increase of activation of additional muscle groups, intensification of the respiratory muscle activity, recruitment of type II muscle fibres, increase of muscle temperature, increase of the basal metabolic rate, lactate and hydrogen ion accumulation, proton leak through the inner mitochondrial membrane, slipping of the ATP synthase and a decrease in the cytosolic phosphorylation potential, are discussed. Finally, an original own model describing the sequence of events leading to the non-proportional increase of oxygen cost of work at a high exercise intensity is presented.

  8. Analysis of heart rate and oxygen uptake kinetics studied by two different pseudo-random binary sequence work rate amplitudes.

    Science.gov (United States)

    Drescher, U; Koschate, J; Schiffer, T; Schneider, S; Hoffmann, U

    2017-06-01

    The aim of the study was to compare the kinetics responses of heart rate (HR), pulmonary (V˙O 2 pulm) and predicted muscular (V˙O 2 musc) oxygen uptake between two different pseudo-random binary sequence (PRBS) work rate (WR) amplitudes both below anaerobic threshold. Eight healthy individuals performed two PRBS WR protocols implying changes between 30W and 80W and between 30W and 110W. HR and V˙O 2 pulm were measured beat-to-beat and breath-by-breath, respectively. V˙O 2 musc was estimated applying the approach of Hoffmann et al. (Eur J Appl Physiol 113: 1745-1754, 2013) considering a circulatory model for venous return and cross-correlation functions (CCF) for the kinetics analysis. HR and V˙O 2 musc kinetics seem to be independent of WR intensity (p>0.05). V˙O 2 pulm kinetics show prominent differences in the lag of the CCF maximum (39±9s; 31±4s; p<0.05). A mean difference of 14W between the PRBS WR amplitudes impacts venous return significantly, while HR and V˙O 2 musc kinetics remain unchanged. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Diffusion-controlled interface kinetics-inclusive system-theoretic propagation models for molecular communication systems

    Science.gov (United States)

    Chude-Okonkwo, Uche A. K.; Malekian, Reza; Maharaj, B. T.

    2015-12-01

    Inspired by biological systems, molecular communication has been proposed as a new communication paradigm that uses biochemical signals to transfer information from one nano device to another over a short distance. The biochemical nature of the information transfer process implies that for molecular communication purposes, the development of molecular channel models should take into consideration diffusion phenomenon as well as the physical/biochemical kinetic possibilities of the process. The physical and biochemical kinetics arise at the interfaces between the diffusion channel and the transmitter/receiver units. These interfaces are herein termed molecular antennas. In this paper, we present the deterministic propagation model of the molecular communication between an immobilized nanotransmitter and nanoreceiver, where the emission and reception kinetics are taken into consideration. Specifically, we derived closed-form system-theoretic models and expressions for configurations that represent different communication systems based on the type of molecular antennas used. The antennas considered are the nanopores at the transmitter and the surface receptor proteins/enzymes at the receiver. The developed models are simulated to show the influence of parameters such as the receiver radius, surface receptor protein/enzyme concentration, and various reaction rate constants. Results show that the effective receiver surface area and the rate constants are important to the system's output performance. Assuming high rate of catalysis, the analysis of the frequency behavior of the developed propagation channels in the form of transfer functions shows significant difference introduce by the inclusion of the molecular antennas into the diffusion-only model. It is also shown that for t > > 0 and with the information molecules' concentration greater than the Michaelis-Menten kinetic constant of the systems, the inclusion of surface receptors proteins and enzymes in the models

  10. Hydrodynamic chronoamperometry for probing kinetics of anaerobic microbial metabolism - case study of Faecalibacterium prausnitzii

    Science.gov (United States)

    Prévoteau, Antonin; Geirnaert, Annelies; Arends, Jan B. A.; Lannebère, Sylvain; van de Wiele, Tom; Rabaey, Korneel

    2015-07-01

    Monitoring in vitro the metabolic activity of microorganisms aids bioprocesses and enables better understanding of microbial metabolism. Redox mediators can be used for this purpose via different electrochemical techniques that are either complex or only provide non-continuous data. Hydrodynamic chronoamperometry using a rotating disc electrode (RDE) can alleviate these issues but was seldom used and is poorly characterized. The kinetics of Faecalibacterium prausnitzii A2-165, a beneficial gut microbe, were determined using a RDE with riboflavin as redox probe. This butyrate producer anaerobically ferments glucose and reduces riboflavin whose continuous monitoring on a RDE provided highly accurate kinetic measurements of its metabolism, even at low cell densities. The metabolic reaction rate increased linearly over a broad range of cell concentrations (9 × 104 to 5 × 107 cells.mL-1). Apparent Michaelis-Menten kinetics was observed with respect to riboflavin (KM = 6 μM kcat = 5.3×105 s-1, at 37 °C) and glucose (KM = 6 μM kcat = 2.4 × 105 s-1). The short temporal resolution allows continuous monitoring of fast cellular events such as kinetics inhibition with butyrate. Furthermore, we detected for the first time riboflavin reduction by another potential probiotic, Butyricicoccus pullicaecorum. The ability of the RDE for fast, accurate, simple and continuous measurements makes it an ad hoc tool for assessing bioprocesses at high resolution.

  11. FET PET for the evaluation of untreated gliomas: correlation of FET uptake and uptake kinetics with tumour grading

    International Nuclear Information System (INIS)

    Poepperl, Gabriele; Koch, Walter; Gildehaus, Franz J.; Tatsch, Klaus; Kreth, Friedrich W.; Mehrkens, Jan H.; Tonn, Joerg C.; Herms, Jochen; Kretzschmar, Hans A.; Seelos, Klaus

    2007-01-01

    Treatment and prognosis of gliomas depend on their histological tumour grade. The aim of the study was to evaluate the potential of [ 18 F]fluoroethyltyrosine (FET) PET for non-invasive tumour grading in untreated patients. Dynamic FET PET studies were performed in 54 patients who, based on MRI, were estimated to have low grade (LG; n = 20), intermediate (WHO II-III; n = 4) or high grade (HG; n = 30) tumours. For standard evaluation, tumour SUV max and the ratio to background (SUV max /BG) were calculated (sum image: 20-40 min). For dynamic evaluation, mean SUV values within a 90% isocontour ROI (SUV90) and the SUV90/BG ratios were determined for each time frame to evaluate the course of FET uptake. Results were correlated with histopathological findings from PET-guided stereotactic biopsies. Histology revealed gliomas in all patients. Using the standard method a statistically significant difference (p = 0.001) was found between LG (n = 20; SUV max /BG: 2.16 ± 0.98) and HG (n = 34; SUV max /BG: 3.29 ± 1.06) gliomas (opt. threshold 2.58: SN71%/SP85%/area under ROC curve [AUC]:0.798), however, with a marked overlap between WHO II to IV tumours. Time activity curves showed slight increase in LG, whereas HG tumours presented with an early peak (10-20 min) followed by a decrease. Dynamic evaluation successfully separated LG from HG gliomas with higher diagnostic accuracy (SN94%/SP100%/AUC:0.967). Based on the ratio-based method, a statistically significant difference was found between LG and HG gliomas. Due to the interindividual variability, however, no reliable individual grading was possible. In contrast, dynamic evaluation allowed LG and HG gliomas to be differentiated with high diagnostic power and, thus, should supplement the conventional method. (orig.)

  12. Kinetic characterization of a novel acid ectophosphatase from Enterobacter asburiae.

    Science.gov (United States)

    Sato, Vanessa Sayuri; Galdiano Júnior, Renato F; Rodrigues, Gisele Regina; Lemos, Eliana G M; Pizauro Junior, João Martins

    2016-02-01

    Expression of acid ectophosphatase by Enterobacter asburiae, isolated from Cattleya walkeriana (Orchidaceae) roots and identified by the 16S rRNA gene sequencing analysis, was strictly regulated by phosphorus ions, with its optimal activity being observed at an inorganic phosphate concentration of 7 mM. At the optimum pH 3.5, intact cells released p-nitrophenol at a rate of 350.76 ± 13.53 nmol of p-nitrophenolate (pNP)/min/10(8) cells. The membrane-bound enzyme was obtained by centrifugation at 100,000 × g for 1 h at 4 °C. p-Nitrophenylphosphate (pNPP) hydrolysis by the enzyme follows "Michaelis-Menten" kinetics with V = 61.2 U/mg and K0.5 = 60 μM, while ATP hydrolysis showed V = 19.7 U/mg, K0.5 = 110 μM, and nH = 1.6 and pyrophosphate hydrolysis showed V = 29.7 U/mg, K0.5 = 84 μM, and nH = 2.3. Arsenate and phosphate were competitive inhibitors with K i = 0.6 mM and K i = 1.8 mM, respectively. p-Nitrophenyl phosphatase (pNPPase) activity was inhibited by vanadate, while p-hydroxymercuribenzoate, EDTA, calcium, copper, and cobalt had no inhibitory effects. Magnesium ions were stimulatory (K0.5 = 2.2 mM and nH = 0.5). Production of an acid ectophosphatase can be a mechanism for the solubilization of mineral phosphates by microorganisms such as Enterobacter asburiae that are versatile in the solubilization of insoluble minerals, which, in turn, increases the availability of nutrients for plants, particularly in soils that are poor in phosphorus.

  13. Tritiated water uptake kinetics in tissue-free water and organically-bound fractions of tomato plants

    International Nuclear Information System (INIS)

    Spencer, F.S.

    1984-03-01

    The kinetics of tritiated water (HTO) vapour uptake into tissue-free water tritium (TFWT) and organically bound tritium (OBT) fractions of tomato, Lycopersicon esculentum Mill., cv Vendor, were investigated under controlled growing conditions. Most uptake data fitted a first-order kinetic model, C t = C ∞ (1-e -kt ), where C t is the tritium concentration at time t, Ca the steady-state concentration and k the uptake rate constant. During atmospheric-HTO exposure with clean-water irrigation in open pots the TFWT k values were 0.024 ± 0.023 h -1 for new foliage, 0.104 ± 0.067 h -1 for old foliage and 0.042 ± to 0.136 h -1 for new green fruit. OBT uptake rate constants were 20 percent less for new foliage and 76 percent less for new green fruit. Under steady-state conditions the ratio of tritium specific activities of TWFT to atmospheric HTO were 0.43 in new foliage, 0.46 in old foliage and 0.19 in green fruit. Within the plant, OBT and TFWT ratios were 0.70 for new foliage, 0.63 for old foliage (maximum) and between 0.72 and 1.92 for green fruit. The greater than unity tritium specific activity ratios in green fruit were not attributed to tritium enrichment but rather to the translocation of foliar OBT to the growing fruit which contained lower specific activity TFWT derived from soil water

  14. High-dose inhaled salbutamol has no acute effects on aerobic capacity or oxygen uptake kinetics in healthy trained men

    DEFF Research Database (Denmark)

    Elers, J; Mørkeberg, Jakob; Jansen, T

    2012-01-01

    enrolled nine healthy well-trained men in a randomized, blinded, placebo-controlled crossover study. Subjects were randomized to inhalation of 40 puffs of 0.2 mg salbutamol or two placebo tablets and performed an incremental test to exhaustion and three submaximal tests at 75% of peak power to determine...... oxygen uptake kinetics. During the incremental test, there were no effects of inhaled salbutamol on VO(2max) in absolute or relative terms, and no effect on peak power and lactate threshold. During the submaximal test, we found no effects on the time constant, time delay, the mean response time or O(2...

  15. Uptake of phosphorus from surfactant solutions by wheat leaves: spreading kinetics, wetted area, and drying time.

    Science.gov (United States)

    Peirce, Courtney A E; Priest, Craig; McBeath, Therese M; McLaughlin, Mike J

    2016-01-07

    The delivery and uptake of nutrients at the surface of plant leaves is an important physicochemical phenomenon that depends on leaf surface morphology and chemistry, fertilizer formulation chemistry (including adjuvant and associated surfactants), wetting dynamics, and many other physical, chemical and biological factors. In this study, the role of spreading dynamics in determining uptake of the macronutrient phosphorus from phosphoric acid fertilizer solution in combination with three different adjuvants was measured in the absence of droplet run-off and splashing. When run-off and splashing losses were zero, spreading and drying rates had a small to negligible effect on the uptake efficiency. The results suggest that uptake may be much less sensitive to the specific choice of adjuvant and long time-scale spreading behaviour than one might intuitively expect.

  16. Spatiotemporal variation of nitrate uptake kinetics within the maize (Zea mays L.) root system is associated with greater nitrate uptake and interactions with architectural phenes.

    Science.gov (United States)

    York, Larry M; Silberbush, Moshe; Lynch, Jonathan P

    2016-06-01

    Increasing maize nitrogen acquisition efficiency is a major goal for the 21st century. Nitrate uptake kinetics (NUK) are defined by I max and K m, which denote the maximum uptake rate and the affinity of transporters, respectively. Because NUK have been studied predominantly at the molecular and whole-root system levels, little is known about the functional importance of NUK variation within root systems. A novel method was created to measure NUK of root segments that demonstrated variation in NUK among root classes (seminal, lateral, crown, and brace). I max varied among root class, plant age, and nitrate deprivation combinations, but was most affected by plant age, which increased I max, and nitrate deprivation time, which decreased I max K m was greatest for crown roots. The functional-structural simulation SimRoot was used for sensitivity analysis of plant growth to root segment I max and K m, as well as to test interactions of I max with root system architectural phenes. Simulated plant growth was more sensitive to I max than K m, and reached an asymptote near the maximum I max observed in the empirical studies. Increasing the I max of lateral roots had the largest effect on shoot growth. Additive effects of I max and architectural phenes on nitrate uptake were observed. Empirically, only lateral root tips aged 20 d operated at the maximum I max, and simulations demonstrated that increasing all seminal and lateral classes to this maximum rate could increase plant growth by as much as 26%. Therefore, optimizing I max for all maize root classes merits attention as a promising breeding goal. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.

  17. Endocytosis of the major yolk proteins of the silkmoth, Hyalophora cecropia: Uptake kinetics and interactions

    International Nuclear Information System (INIS)

    Kulakosky, P.C.

    1989-01-01

    The oocytes of Lepidopteran insects take up several yolk proteins in defined proportions even though their relative availability in the hemolymph changes during the several days required to complete yolk formation in all the eggs. There are three hemolymph yolk precursors, vitellogenin, microvitellogenin and lipophorin; one precursor, paravitellogenin is produced in the ovary. The control mechanism for their proportional endocytosis is not known. In this thesis, the author describe the purification of all four proteins and the radiolabeling of the hemolymph precursors. The radiolabeled proteins were tested with an in vitro incubation system to assess the biological activity of the proteins and the reliability of the incubation methods. All of the labeled probes were transferred from the incubation medium to yolk spheres within the oocyte in a saturable, energy-dependent, and stage-specific manner. The rates of uptake were similar to the estimated rates of uptake in situ. The concentration dependence of in vitro uptake was investigated and found to be consistent with in situ concentrations and the composition of yolk in mature eggs. Two precursors, vitellogenin and lipophorin, competed for uptake indicating that they share a common binding site while the third, microvitellin, did not compete with the others. Though vitellogenin and lipophorin competed for uptake, only vitellogenin displayed the unique ability to increase the uptake rate of microvitellin and fluid in vitro

  18. Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors.

    Science.gov (United States)

    Milanovsky, Georgy E; Petrova, Anastasia A; Cherepanov, Dmitry A; Semenov, Alexey Yu

    2017-09-01

    The reduction kinetics of the photo-oxidized primary electron donor P 700 in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P 700 , secondary quinone acceptor A 1 , iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl 2 NQ) and oxygen. PS I complexes containing various quinones in the A 1 -binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl 2 NQ) as well as F X -core complexes, depleted of terminal iron-sulfur F A /F B clusters, were studied. The acceleration of charge recombination in F X -core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A 1 -binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P 700 + reduction with the kinetic model. The free energy gap ΔG 0 between F X and F A /F B clusters was estimated as -130 meV. The driving force of ET from A 1 to F X was determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A 1A -site, this reaction was found to be endergonic (ΔG 0  = +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from F A /F B , F X and Cl 2 NQ in the A 1 -site of PS I to external acceptors were estimated. The side production of superoxide radical in the A 1 -site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.

  19. A graphical user interface for a method to infer kinetics and network architecture (MIKANA).

    Science.gov (United States)

    Mourão, Márcio A; Srividhya, Jeyaraman; McSharry, Patrick E; Crampin, Edmund J; Schnell, Santiago

    2011-01-01

    One of the main challenges in the biomedical sciences is the determination of reaction mechanisms that constitute a biochemical pathway. During the last decades, advances have been made in building complex diagrams showing the static interactions of proteins. The challenge for systems biologists is to build realistic models of the dynamical behavior of reactants, intermediates and products. For this purpose, several methods have been recently proposed to deduce the reaction mechanisms or to estimate the kinetic parameters of the elementary reactions that constitute the pathway. One such method is MIKANA: Method to Infer Kinetics And Network Architecture. MIKANA is a computational method to infer both reaction mechanisms and estimate the kinetic parameters of biochemical pathways from time course data. To make it available to the scientific community, we developed a Graphical User Interface (GUI) for MIKANA. Among other features, the GUI validates and processes an input time course data, displays the inferred reactions, generates the differential equations for the chemical species in the pathway and plots the prediction curves on top of the input time course data. We also added a new feature to MIKANA that allows the user to exclude a priori known reactions from the inferred mechanism. This addition improves the performance of the method. In this article, we illustrate the GUI for MIKANA with three examples: an irreversible Michaelis-Menten reaction mechanism; the interaction map of chemical species of the muscle glycolytic pathway; and the glycolytic pathway of Lactococcus lactis. We also describe the code and methods in sufficient detail to allow researchers to further develop the code or reproduce the experiments described. The code for MIKANA is open source, free for academic and non-academic use and is available for download (Information S1).

  20. Kinetics and autoradiography of high affinity uptake of serotonin by primary astrocyte cultures

    International Nuclear Information System (INIS)

    Katz, D.M.; Kimelberg, H.K.

    1985-01-01

    Primary astrocyte cultures prepared from the cerebral cortices of neonatal rats showed significant accumulation of serotonin (5-hydroxytryptamine; [ 3 H]-5-HT). At concentrations in the range of 0.01 to 0.7 microM [ 3 H]-5-HT, this uptake was 50 to 85% Na+ dependent and gave a Km of 0.40 +/- 0.11 microM [ 3 H]-5-HT and a Vmax of 6.42 +/- 0.85 (+/- SEM) pmol of [ 3 H]-5-HT/mg of protein/4 min for the Na+-dependent component. In the absence of Na+ the uptake was nonsaturable. Omission of the monoamine oxidase inhibitor pargyline markedly reduced the Na+-dependent component of [ 3 H]-5-HT uptake but had a negligible effect on the Na+-independent component. This suggest significant oxidative deamination of serotonin after it has been taken up by the high affinity system, followed by release of its metabolite. The authors estimated that this system enabled the cells to concentrate [ 3 H]-5-HT up to 44-fold at an external [ 3 H]-5-HT concentration of 10(-7) M. Inhibition of [ 3 H]-5-HT uptake by a number of clinically effective antidepressants was also consistent with a specific high affinity uptake mechanism for 5-HT, the order of effectiveness of inhibition being chlorimipramine greater than fluoxetine greater than imipramine = amitriptyline greater than desmethylimipramine greater than iprindole greater than mianserin. Uptake of [ 3 H]-5-HT was dependent on the presence of Cl- as well as Na+ in the medium, and the effect of omission of both ions was nonadditive. Varying the concentration of K+ in the media from 1 to 50 mM had a limited effect on [ 3 H]-5-HT uptake

  1. Determination of Unbound Partition Coefficient and in Vitro-in Vivo Extrapolation for SLC13A Transporter-Mediated Uptake.

    Science.gov (United States)

    Riccardi, Keith; Li, Zhenhong; Brown, Janice A; Gorgoglione, Matthew F; Niosi, Mark; Gosset, James; Huard, Kim; Erion, Derek M; Di, Li

    2016-10-01

    Unbound partition coefficient (Kpuu) is important to an understanding of the asymmetric free drug distribution of a compound between cells and medium in vitro, as well as between tissue and plasma in vivo, especially for transporter-mediated processes. Kpuu was determined for a set of compounds from the SLC13A family that are inhibitors and substrates of transporters in hepatocytes and transporter-transfected cell lines. Enantioselectivity was observed, with (R)-enantiomers achieving much higher Kpuu (>4) than the (S)-enantiomers (<1) in human hepatocytes and SLC13A5-transfected human embryonic 293 cells. The intracellular free drug concentration correlated directly with in vitro pharmacological activity rather than the nominal concentration in the assay because of the high Kpuu mediated by SLC13A5 transporter uptake. Delivery of the diacid PF-06649298 directly or via hydrolysis of the ethyl ester prodrug PF-06757303 resulted in quite different Kpuu values in human hepatocytes (Kpuu of 3 for diacid versus 59 for prodrug), which was successfully modeled on the basis of passive diffusion, active uptake, and conversion rate from ester to diacid using a compartmental model. Kpuu values changed with drug concentrations; lower values were observed at higher concentrations possibly owing to a saturation of transporters. Michaelis-Menten constant (Km) of SLC13A5 was estimated to be 24 μM for PF-06649298 in human hepatocytes. In vitro Kpuu obtained from rat suspension hepatocytes supplemented with 4% fatty acid free bovine serum albumin showed good correlation with in vivo Kpuu of liver-to-plasma, illustrating the potential of this approach to predict in vivo Kpuu from in vitro systems. Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.

  2. Effects of dipyridamole-induced vasodilation on myocardial uptake and clearance kinetics of thallium-201

    International Nuclear Information System (INIS)

    Beller, G.A.; Holzgrefe, H.H.; Watson, D.D.

    1983-01-01

    Myocardial thallium-201 (201Tl) uptake and clearance after intravenous administration of dipyridamole (150 micrograms/kg) were determined in 12 open-chest anesthetized dogs with a partial coronary artery stenosis. 201Tl (1.5 mCi) was injected intravenously and myocardial biopsy specimens were obtained 10 min, 60 min, and 2 hr after injection. Serial changes in 201Tl activity in the normal zone and in the zone of partial stenosis were correlated with microsphere-determined regional blood flow and distal coronary pressure. Another nine dogs with equivalent stenosis not given dipyridamole before 201Tl served as controls. Data indicate that dipyridamole-induced vasodilation in the presence of a partial stenosis results in diminished uptake and delayed clearance compared with increased uptake and more rapid clearance in normally perfused myocardium producing an initial 201Tl defect with delayed redistribution

  3. Differential potassium influx influences growth of two cotton varieties in hydroponics

    International Nuclear Information System (INIS)

    Ali, L.; Maqsood, M.A.; Kanwal, S.; Aziz, T.

    2010-01-01

    Potassium uptake rate of two cotton (Gossypium hirsutum L.) varieties viz., NIBGE-2 and MNH-786 was investigated in nutrient solution culture having deficient K at the rate 0.3 mM and deficient K+ Na at the rate 0.3 +2.7 mM. Depletion of K from solution was monitored over a period of 24 h at regular time intervals after 0, 0.5, 1.0, 1.5, 2, 3, 4, 5, 6, 8, 10, 12 and 24 h to estimate K uptake kinetics of the roots i.e. maximum influx, I/sub max/ and the Michaelis-Menten constant, Km. NIBGE-2 had about 2-fold higher (2.0 mg g rdw-1 hr-1) I/sub max/ value for K uptake rate at deficient K+Na than that (1.207 mg g rdw-1 hr-1) for MNH-786. Higher, Michaelis-Menten constant, Km (12.82 ppm) for K uptake rate was observed in both cultivars NIBGE-2 and MNH-786 at deficient K+Na than that at deficient K. Main effects of treatments and varieties had significant (p< 0.05) effect on shoot dry matter, root dry matter, total dry matter and leaf area per plant. Maximum K influx in NIBGE-2 at deficient K and deficient K +Na was attributed to enhanced growth response as compared to that in MNH-786. (author)

  4. Uptake and kinetics of 226Ra, 210Pb and 210Po in big sage brush

    International Nuclear Information System (INIS)

    Simon, S.L.

    1985-01-01

    Root uptake of 226 Pb and 210 Po by mature sage brush was studied using a soil injection method for spiking the soil with minimal root disturbance. The main objective was to measure vegetation concentrations and determine concentration ratios (CR's) due to root uptake as a function of time in mature big sage brush. Concentration ratios obtained in mature vegetation and in steady-state situations may be valuable in assessing the impact of uranium mining and milling. The vegetation was sampled approximately every 3 mo for A 2 y period. Significant levels of activity were detected in the vegetation beginning at the first sampling (81 d after soil injection for 226 Ra, 28 d for 210 Pb and 210 Po). There was an exponential decrease in concentration to an apparent steady state value. Mean values (geometric) of the data pooled over the second year period indicated that steady-state Cr's for 226 Ra, 210 Pb and 210 Po, as determined in mature sage brush, were 0.04, 0.009, and 0.08, respectively. Investigations were also carried out to verify the suitability of soil injection for uptake studies and to evaluate the time dependence of 226 Ra leaching from sage brush leaves. The soil injection method was determined to produce, on the average, uptake equivalent to that produce by a uniform soil distribution, however, the variety of uptake for plants growing in injected soil was higher than for plants growing in uniformly contaminated soil. A three compartment mathematical model was formulated to help understand mechanisms of plant uptake and to predict, if possible, the concentration of 226 Ra, 210 Po in vegetation as a function of time after soil spiking

  5. Non-invasive differentiation of pancreatic lesions: is analysis of FDG kinetics superior to semiquantitative uptake value analysis?

    International Nuclear Information System (INIS)

    Nitzsche, E.U.; Hoegerle, S.; Mix, M.; Brink, I.; Otte, A.; Moser, E.

    2002-01-01

    The diagnostic utility of fluorine-18 2-deoxy-D-glucose positron emission tomography (FDG PET) for the non-invasive differentiation of focal pancreatic lesions originating from cancer or chronic pancreatitis by combined visual image interpretation and semiquantitative uptake value analysis has been documented. However, in clinical routine some misdiagnosis is still observed. This is because there is potential overlap between the semiquantitative uptake values obtained for active inflammatory lesions and cancer. Therefore, this prospective study was undertaken to test the hypothesis that analysis of dynamic kinetics of focal pancreatic lesions based on FDG PET may more accurately determine the benign or malignant nature of such lesions. Thirty patients (56±17 years) were studied dynamically with FDG PET for a period of 60-90 min. Patients were assigned to one of four groups: control, acute pancreatitis, chronic pancreatitis or pancreatic cancer. Two observers, blinded to the clinical data, analysed the time-activity curves of FDG kinetics based on region of interest analysis. The diagnosis predicted by FDG PET was compared with the result of histological examination of the surgical specimen. Analysis of FDG kinetics revealed significant differences in the shape of the time-activity curve for controls, pancreatic cancer and inflammatory disease. Surprisingly, there was no significant difference in the time-activity curve shape for chronic pancreatitis and acute pancreatitis; this is, however, not a clinical issue. Furthermore, acquisition time (60 min vs 90 min) did not affect interpretation of the time-activity curve, so that scanning time may be regularly shortened to 60 min. Interobserver agreement was 1. Based on these findings, non-invasive differentiation between pancreatic cancer and chronic pancreatitis was correctly predicted in all cases, as confirmed by histology. In addition, the specificity was increased compared with that obtained from standardised

  6. Training-induced acceleration of O(2) uptake on-kinetics precedes muscle mitochondrial biogenesis in humans.

    Science.gov (United States)

    Zoladz, Jerzy A; Grassi, Bruno; Majerczak, Joanna; Szkutnik, Zbigniew; Korostyński, Michał; Karasiński, Janusz; Kilarski, Wincenty; Korzeniewski, Bernard

    2013-04-01

    The effects of 5 weeks of moderate-intensity endurance training on pulmonary oxygen uptake kinetics (V(O(2)) on-kinetics) were studied in 15 healthy men (mean ± SD: age 22.7 ± 1.8 years, body weight 76.4 ± 8.9 kg and maximal V(O(2)) 46.0 ± 3.7 ml kg(-1) min(-1)). Training caused a significant acceleration (P = 0.003) of V(O(2)) on-kinetics during moderate-intensity cycling (time constant of the 'primary' component 30.0 ± 6.6 versus 22.8 ± 5.6 s before and after training, respectively) and a significant decrease (P = 0.04) in the amplitude of the primary component (837 ± 351 versus 801 ± 330 ml min(-1)). No changes in myosin heavy chain distribution, muscle fibre capillarization, level of peroxisome proliferator-activated receptor γ coactivator 1α and other markers of mitochondrial biogenesis (mitochondrial DNA copy number, cytochrome c and cytochrome oxidase subunit I contents) in the vastus lateralis were found after training. A significant downregulation in the content of the sarcoplasmic reticulum ATPase 2 (SERCA2; P = 0.03) and a tendency towards a decrease in SERCA1 (P = 0.055) was found after training. The decrease in SERCA1 was positively correlated (P = 0.05) with the training-induced decrease in the gain of the V(O(2)) on-kinetics (ΔV(O(2)) at steady state/Δpower output). In the early stage of training, the acceleration in V(O(2)) on-kinetics during moderate-intensity cycling can occur without enhanced mitochondrial biogenesis or changes in muscle myosin heavy chain distribution and in muscle fibre capillarization. The training-induced decrease of the O(2) cost of cycling could be caused by the downregulation of SERCA pumps.

  7. A kinetic study of cation release from a mixed mineral assemblage: implications for determination of uranium uptake

    International Nuclear Information System (INIS)

    Fenton, B.R.; Waite, T.D.

    1996-01-01

    The uptake of U(VI) as UO 2+ 2 on a natural complex mineral assemblage has been studied using batch selective chemical extraction techniques and secondary ion mass spectroscopy (SIMS). Sediments used in the study consisted of a quartz/mica schist collected from the locale of the Koongarra Uranium ore body, Alligator Rivers Uranium Province, Northern Territory, Australia. The bulk sediment was gravity separated into four size fractions, with attention focused on the nominally <25 μm and 250-1000 μm fractions of the bulk sample, in order to assess the effects of particle size on uranium uptake. Investigation of the kinetics of elemental release in the presence of selective extractants show that uranium is bound largely within the iron and aluminium oxyhydroxides of the assemblage, with a highly mobile fraction of this associated with aluminol sites. SIMS analysis of the natural substrate confirms that significant quantities of aluminium are present in surface layers. The effect of particle size on the uptake of uranium indicates very little change with respect to particle size. This finding may be attributed to the presence of highly porous surface coatings. (orig.)

  8. Toxicological effects of multi-walled carbon nanotubes on Saccharomyces cerevisiae: The uptake kinetics and mechanisms and the toxic responses

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Song; Zhu, Bin; Huang, Aiguo [College of Animal Science and Technology, Northwest A& F University, Yangling 712100 (China); Hu, Yang [College of Science, Northwest A& F University, Yangling 712100 (China); Wang, Gaoxue, E-mail: wanggaoxue@126.com [College of Animal Science and Technology, Northwest A& F University, Yangling 712100 (China); Ling, Fei, E-mail: feiling@nwsuaf.edu.cn [College of Animal Science and Technology, Northwest A& F University, Yangling 712100 (China)

    2016-11-15

    Highlights: • MWCNTs (<100 mg/L) were not toxic to S. cerevisiae. • MWCNTs were internalized in S. cerevisiae cells by three pathways. • The uptake kinetics and the subcellular distribution of MWCNTs in S. cerevisiae cells were shown. • S. cerevisiae cells were undergoing apoptosis by mitochondrial impairment pathway. - Abstract: Using Saccharomyces cerevisiae as an experimental model, the potential toxicological effects of oxidized multi-walled carbon nanotubes (MWCNTs) were investigated following exposure to 0–600 mg/L for 24 h. Results indicated that MWCNTs (>100 mg/L) had adverse effects on the cell proliferation. MWCNTs were clearly visible in lysosome, vacuole, endosome, mitochondria, multivesicular body and localization in the perinuclear region. The uptake kinetics data demonstrated that the maximum MWCNTs content (209.61 mg/g) was reached at 3 h, and a steady state was reached after 18 h. Based on the combined results of transmission electron microscope, endocytosis inhibition experiments and endocytosis-related genes (END3, END6, Sla2 and Rsp5) expression analysis, we elucidated MWCNTs uptake mechanism: (i) via a direct penetration of single MWCNTs; (ii) via endocytosis of single MWCNTs; and (iii) via endocytosis of MWCNTs aggregates. The percentage of apoptosis was significant increased at 600 mg/L. The decrease of mitochondrial transmembrane potential and the leakage of cytochrome c shown dose-dependent manners. Interestingly, there was no significant increase of reactive oxygen species (ROS). The apoptosis-related genes (SOD1, SOD2, Yca1, Nma111 and Nuc1) were significant changed. These results obtained in our study demonstrated that oxidized MWCNTs induce Saccharomyces cerevisiae apoptosis via mitochondrial impairment pathway.

  9. Sub-minute kinetics of human red cell fumarase: 1 H spin-echo NMR spectroscopy and 13 C rapid-dissolution dynamic nuclear polarization.

    Science.gov (United States)

    Shishmarev, Dmitry; Wright, Alan J; Rodrigues, Tiago B; Pileio, Giuseppe; Stevanato, Gabriele; Brindle, Kevin M; Kuchel, Philip W

    2018-03-01

    Fumarate is an important probe of metabolism in hyperpolarized magnetic resonance imaging and spectroscopy. It is used to detect the release of fumarase in cancer tissues, which is associated with necrosis and drug treatment. Nevertheless, there are limited reports describing the detailed kinetic studies of this enzyme in various cells and tissues. Thus, we aimed to evaluate the sub-minute kinetics of human red blood cell fumarase using nuclear magnetic resonance (NMR) spectroscopy, and to provide a quantitative description of the enzyme that is relevant to the use of fumarate as a probe of cell rupture. The fumarase reaction was studied using time courses of 1 H spin-echo and 13 C-NMR spectra. 1 H-NMR experiments showed that the fumarase reaction in hemolysates is sufficiently rapid to make its kinetics amenable to study in a period of approximately 3 min, a timescale characteristic of hyperpolarized 13 C-NMR spectroscopy. The rapid-dissolution dynamic nuclear polarization (RD-DNP) technique was used to hyperpolarize [1,4- 13 C]fumarate, which was injected into concentrated hemolysates. The kinetic data were analyzed using recently developed FmR α analysis and modeling of the enzymatic reaction using Michaelis-Menten equations. In RD-DNP experiments, the decline in the 13 C-NMR signal from fumarate, and the concurrent rise and fall of that from malate, were captured with high spectral resolution and signal-to-noise ratio, which allowed the robust quantification of fumarase kinetics. The kinetic parameters obtained indicate the potential contribution of hemolysis to the overall rate of the fumarase reaction when 13 C-NMR RD-DNP is used to detect necrosis in animal models of implanted tumors. The analytical procedures developed will be applicable to studies of other rapid enzymatic reactions using conventional and hyperpolarized substrate NMR spectroscopy. Copyright © 2018 John Wiley & Sons, Ltd.

  10. Understanding the in vivo uptake kinetics of a phosphatidylethanolamine-binding agent 99mTc-Duramycin

    International Nuclear Information System (INIS)

    Audi, Said; Li Zhixin; Capacete, Joseph; Liu Yu; Fang, Wei; Shu, Laura G.; Zhao Ming

    2012-01-01

    Introduction: 99m Tc-Duramycin is a peptide-based molecular probe that binds specifically to phosphatidylethanolamine (PE). The goal was to characterize the kinetics of molecular interactions between 99m Tc-Duramycin and the target tissue. Methods: High level of accessible PE is induced in cardiac tissues by myocardial ischemia (30 min) and reperfusion (120 min) in Sprague–Dawley rats. Target binding and biodistribution of 99m Tc-duramycin were captured using SPECT/CT. To quantify the binding kinetics, the presence of radioactivity in ischemic versus normal cardiac tissues was measured by gamma counting at 3, 10, 20, 60 and 180 min after injection. A partially inactivated form of 99m Tc-Duramycin was analyzed in the same fashion. A compartment model was developed to quantify the uptake kinetics of 99m Tc-Duramycin in normal and ischemic myocardial tissue. Results: 99m Tc-duramycin binds avidly to the damaged tissue with a high target-to-background radio. Compartment modeling shows that accessibility of binding sites in myocardial tissue to 99m Tc-Duramycin is not a limiting factor and the rate constant of target binding in the target tissue is at 2.2 ml/nmol/min/g. The number of available binding sites for 99m Tc-Duramycin in ischemic myocardium was estimated at 0.14 nmol/g. Covalent modification of D15 resulted in a 9-fold reduction in binding affinity. Conclusion: 99m Tc-Duramycin accumulates avidly in target tissues in a PE-dependent fashion. Model results reflect an efficient uptake mechanism, consistent with the low molecular weight of the radiopharmaceutical and the relatively high density of available binding sites. These data help better define the imaging utilities of 99m Tc-Duramycin as a novel PE-binding agent.

  11. Mechanistic kinetic modeling generates system-independent P-glycoprotein mediated transport elementary rate constants for inhibition and, in combination with 3D SIM microscopy, elucidates the importance of microvilli morphology on P-glycoprotein mediated efflux activity.

    Science.gov (United States)

    Ellens, Harma; Meng, Zhou; Le Marchand, Sylvain J; Bentz, Joe

    2018-06-01

    In vitro transporter kinetics are typically analyzed by steady-state Michaelis-Menten approximations. However, no clear evidence exists that these approximations, applied to multiple transporters in biological membranes, yield system-independent mechanistic parameters needed for reliable in vivo hypothesis generation and testing. Areas covered: The classical mass action model has been developed for P-glycoprotein (P-gp) mediated transport across confluent polarized cell monolayers. Numerical integration of the mass action equations for transport using a stable global optimization program yields fitted elementary rate constants that are system-independent. The efflux active P-gp was defined by the rate at which P-gp delivers drugs to the apical chamber, since as much as 90% of drugs effluxed by P-gp partition back into nearby microvilli prior to reaching the apical chamber. The efflux active P-gp concentration was 10-fold smaller than the total expressed P-gp for Caco-2 cells, due to their microvilli membrane morphology. The mechanistic insights from this analysis are readily extrapolated to P-gp mediated transport in vivo. Expert opinion: In vitro system-independent elementary rate constants for transporters are essential for the generation and validation of robust mechanistic PBPK models. Our modeling approach and programs have broad application potential. They can be used for any drug transporter with minor adaptations.

  12. Bilirubin glucuronidation revisited: proper assay conditions to estimate enzyme kinetics with recombinant UGT1A1.

    Science.gov (United States)

    Zhou, Jin; Tracy, Timothy S; Remmel, Rory P

    2010-11-01

    Bilirubin, an end product of heme catabolism, is primarily eliminated via glucuronic acid conjugation by UGT1A1. Impaired bilirubin conjugation, caused by inhibition of UGT1A1, can result in clinical consequences, including jaundice and kernicterus. Thus, evaluation of the ability of new drug candidates to inhibit UGT1A1-catalyzed bilirubin glucuronidation in vitro has become common practice. However, the instability of bilirubin and its glucuronides presents substantial technical challenges to conduct in vitro bilirubin glucuronidation assays. Furthermore, because bilirubin can be diglucuronidated through a sequential reaction, establishment of initial rate conditions can be problematic. To address these issues, a robust high-performance liquid chromatography assay to measure both bilirubin mono- and diglucuronide conjugates was developed, and the incubation conditions for bilirubin glucuronidation by human embryonic kidney 293-expressed UGT1A1 were carefully characterized. Our results indicated that bilirubin glucuronidation should be assessed at very low protein concentrations (0.05 mg/ml protein) and over a short incubation time (5 min) to assure initial rate conditions. Under these conditions, bilirubin total glucuronide formation exhibited a hyperbolic (Michaelis-Menten) kinetic profile with a K(m) of ∼0.2 μM. In addition, under these initial rate conditions, the relative proportions between the total monoglucuronide and the diglucuronide product were constant across the range of bilirubin concentration evaluated (0.05-2 μM), with the monoglucuronide being the predominant species (∼70%). In conclusion, establishment of appropriate incubation conditions (i.e., very low protein concentrations and short incubation times) is necessary to properly characterize the kinetics of bilirubin glucuronidation in a recombinant UGT1A1 system.

  13. Kinetic study of enzymatic hydrolysis of acid-pretreated coconut coir

    Science.gov (United States)

    Fatmawati, Akbarningrum; Agustriyanto, Rudy

    2015-12-01

    Biomass waste utilization for biofuel production such as bioethanol, has become more prominent currently. Coconut coir is one of lignocellulosic food wastes, which is abundant in Indonesia. Bioethanol production from such materials consists of more than one step. Pretreatment and enzymatic hydrolysis is crucial steps to produce sugar which can then be fermented into bioethanol. In this research, ground coconut coir was pretreated using dilute sulfuric acid at 121°C. This pretreatment had increased the cellulose content and decreased the lignin content of coconut coir. The pretreated coconut coir was hydrolyzed using a mix of two commercial cellulase enzymes at pH of 4.8 and temperature of 50°C. The enzymatic hydrolysis was conducted at several initial coconut coir slurry concentrations (0.1-2 g/100 mL) and reaction times (2-72 hours). The reducing sugar concentration profiles had been produced and can be used to obtain reaction rates. The highest reducing sugar concentration obtained was 1,152.567 mg/L, which was produced at initial slurry concentration of 2 g/100 mL and 72 hours reaction time. In this paper, the reducing sugar concentrations were empirically modeled as a function of reaction time using power equations. Michaelis-Menten kinetic model for enzymatic hydrolysis reaction is adopted. The kinetic parameters of that model for sulfuric acid-pretreated coconut coir enzymatic hydrolysis had been obtained which are Vm of 3.587×104 mg/L.h, and KM of 130.6 mg/L.

  14. An Integrated Circuit for Chip-Based Analysis of Enzyme Kinetics and Metabolite Quantification.

    Science.gov (United States)

    Cheah, Boon Chong; Macdonald, Alasdair Iain; Martin, Christopher; Streklas, Angelos J; Campbell, Gordon; Al-Rawhani, Mohammed A; Nemeth, Balazs; Grant, James P; Barrett, Michael P; Cumming, David R S

    2016-06-01

    We have created a novel chip-based diagnostic tools based upon quantification of metabolites using enzymes specific for their chemical conversion. Using this device we show for the first time that a solid-state circuit can be used to measure enzyme kinetics and calculate the Michaelis-Menten constant. Substrate concentration dependency of enzyme reaction rates is central to this aim. Ion-sensitive field effect transistors (ISFET) are excellent transducers for biosensing applications that are reliant upon enzyme assays, especially since they can be fabricated using mainstream microelectronics technology to ensure low unit cost, mass-manufacture, scaling to make many sensors and straightforward miniaturisation for use in point-of-care devices. Here, we describe an integrated ISFET array comprising 2(16) sensors. The device was fabricated with a complementary metal oxide semiconductor (CMOS) process. Unlike traditional CMOS ISFET sensors that use the Si3N4 passivation of the foundry for ion detection, the device reported here was processed with a layer of Ta2O5 that increased the detection sensitivity to 45 mV/pH unit at the sensor readout. The drift was reduced to 0.8 mV/hour with a linear pH response between pH 2-12. A high-speed instrumentation system capable of acquiring nearly 500 fps was developed to stream out the data. The device was then used to measure glucose concentration through the activity of hexokinase in the range of 0.05 mM-231 mM, encompassing glucose's physiological range in blood. Localised and temporal enzyme kinetics of hexokinase was studied in detail. These results present a roadmap towards a viable personal metabolome machine.

  15. Effects of growth rate, cell size, motion, and elemental stoichiometry on nutrient transport kinetics.

    Science.gov (United States)

    Flynn, Kevin J; Skibinski, David O F; Lindemann, Christian

    2018-04-01

    Nutrient acquisition is a critical determinant for the competitive advantage for auto- and osmohetero- trophs alike. Nutrient limited growth is commonly described on a whole cell basis through reference to a maximum growth rate (Gmax) and a half-saturation constant (KG). This empirical application of a Michaelis-Menten like description ignores the multiple underlying feedbacks between physiology contributing to growth, cell size, elemental stoichiometry and cell motion. Here we explore these relationships with reference to the kinetics of the nutrient transporter protein, the transporter rate density at the cell surface (TRD; potential transport rate per unit plasma-membrane area), and diffusion gradients. While the half saturation value for the limiting nutrient increases rapidly with cell size, significant mitigation is afforded by cell motion (swimming or sedimentation), and by decreasing the cellular carbon density. There is thus potential for high vacuolation and high sedimentation rates in diatoms to significantly decrease KG and increase species competitive advantage. Our results also suggest that Gmax for larger non-diatom protists may be constrained by rates of nutrient transport. For a given carbon density, cell size and TRD, the value of Gmax/KG remains constant. This implies that species or strains with a lower Gmax might coincidentally have a competitive advantage under nutrient limited conditions as they also express lower values of KG. The ability of cells to modulate the TRD according to their nutritional status, and hence change the instantaneous maximum transport rate, has a very marked effect upon transport and growth kinetics. Analyses and dynamic models that do not consider such modulation will inevitably fail to properly reflect competitive advantage in nutrient acquisition. This has important implications for the accurate representation and predictive capabilities of model applications, in particular in a changing environment.

  16. Transport and phosphorylation of choline in higher plant cells. Phosphorus-31 nuclear magnetic resonance studies

    Energy Technology Data Exchange (ETDEWEB)

    Bligny, R.; Foray, M.F.; Roby, C.; Douce, R.

    1989-03-25

    When sycamore cells were suspended in basal medium containing choline, the latter was taken up by the cells very rapidly. A facilitated diffusion system appertained at low concentrations of choline and exhibited Michaelis-Menten kinetics. At higher choline concentrations simple diffusion appeared to be the principal mode of uptake. Addition of choline to the perfusate of compressed sycamore cells monitored by /sup 31/P NMR spectroscopy resulted in a dramatic accumulation of P-choline in the cytoplasmic compartment containing choline kinase and not in the vacuole. The total accumulation of P-choline over a 10-h period exhibited Michaelis-Menten kinetics. During this period, in the absence of Pi in the perfusion medium there was a marked depletion of glucose-6-P, and the cytoplasmic Pi resonance disappeared almost completely. When a threshold of cytoplasmic Pi was attained, the phosphorylation of choline was sustained by the continuous release of Pi from the vacuole although at a much lower rate. However, when 100 microM inorganic phosphate was present in the perfusion medium, externally added Pi was preferentially used to sustain P-choline synthesis. It is clear, therefore, that cytosolic choline kinase associated with a carrier-mediated transport system for choline uptake appeared as effective systems for continuously trapping cytoplasmic Pi including vacuolar Pi entering the cytoplasm.

  17. Pulmonary O2 uptake on-kinetics in endurance- and sprint-trained master athletes.

    Science.gov (United States)

    Berger, N J A; Rittweger, J; Kwiet, A; Michaelis, I; Williams, A G; Tolfrey, K; Jones, A M

    2006-12-01

    The purpose of this study was to characterise the VO2 kinetic response to moderate intensity cycle exercise in endurance-trained (END) and sprint or power-trained (SPR) track and field master athletes ranging in age from 45 to 85 years. We hypothesised that the time constant (tau) describing the Phase II VO2 on-response would be smaller in the END compared to the SPR athletes, and that the tau would become greater with increasing age in both groups. Eighty-four master athletes who were competing at either the British or European Veteran Athletics Championships acted as subjects, and were classified as either END (800 m - marathon; n = 41), or SPR (100 - 400 m and field events; n = 43) specialists. Subjects completed two 6 minute "step" transitions to a work rate of moderate intensity on a cycle ergometer and pulmonary gas exchange was measured breath-by-breath. Analysis of variance revealed that SPR athletes had slower VO2 on-kinetics (i.e., greater tau) compared to END athletes at each of the age groups studied: 46 - 55 yrs (END: 25 +/- 6 vs. SPR: 36 +/- 9 s; p kinetics became slower with advancing age in the SPR athletes (p kinetics in SPR compared to END master athletes is consistent both with differences in physiology (e.g., muscle fibre type, oxidative/glycolytic capacity) and training between these specialist athletes. Master END athletes have similar tau values to their younger counterparts (approximately 25 s) suggesting that participation in endurance exercise training limits the slowing of VO2 on-kinetics with age in this population.

  18. Uptake and kinetics of 226Ra, 210Pb and 210Po in big sagebrush

    International Nuclear Information System (INIS)

    Simon, S.L.

    1985-01-01

    Root uptake of 226 Ra, 210 Pb and 210 Po by mature sagebrush was studied using a soil injection method for spiking the soil with minimal root disturbance. The main objective was to measure vegetation concentrations and determine concentration ratios (CR's) due to root uptake as a function of time in mature big sagebrush. Concentration ratios obtained in mature vegetation and in steady-state situations may be valuable in assessing the impact of uranium mining and milling. The vegetation was sampled approximately every 3 months for a 2 year period. Significant levels of activity were detected in the vegetation beginning at the first sampling (81 days after soil injection for 226 Ra, 28 days for 210 Pb and 210 Po). There was an exponential decrease in concentration to an apparent steady-state value. Mean values (geometric) of the data pooled over the second year period indicated that the steady-state CR's for 226 Ra, 210 Pb and 210 Po, as determined in mature sagebrush, were 0.04, 0.009, and 0.08, respectively. A three compartment mathematical model was formulated to help understand mechanisms of plant uptake and to predict, if possible, the concentration of 226 Ra, 210 Pb and 210 Po in vegetation as a function of time after soil spiking. A numerical solution was determined by 'calibrating' the general model solution with constants determined from regressions of concentrations in vegetation, soil leaching and leaf leaching data. Validation of the model is currently not possible because of an absence of similar time-dependent uptake studies. 168 refs., 19 figs., 18 tabs

  19. Effects of multi-frequency power ultrasound on the enzymolysis of corn gluten meal: Kinetics and thermodynamics study.

    Science.gov (United States)

    Jin, Jian; Ma, Haile; Qu, Wenjuan; Wang, Kai; Zhou, Cunshan; He, Ronghai; Luo, Lin; Owusu, John

    2015-11-01

    The effects of multi-frequency power ultrasound (MPU) pretreatment on the kinetics and thermodynamics of corn gluten meal (CGM) were investigated in this research. The apparent constant (KM), apparent break-down rate constant (kA), reaction rate constants (k), energy of activation (Ea), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs free energy of activation (ΔG) were determined by means of the Michaelis-Menten equation, first-order kinetics model, Arrhenius equation and transition state theory, respectively. The results showed that MPU pretreatment can accelerate the enzymolysis of CGM under different enzymolysis conditions, viz. substrate concentration, enzyme concentration, pH, and temperature. Kinetics analysis revealed that MPU pretreatment decreased the KM value by 26.1% and increased the kA value by 7.3%, indicating ultrasound pretreatment increased the affinity between enzyme and substrate. In addition, the values of k for ultrasound pretreatment were increased by 84.8%, 41.9%, 28.9%, and 18.8% at the temperature of 293, 303, 313 and 323 K, respectively. For the thermodynamic parameters, ultrasound decreased Ea, ΔH and ΔS by 23.0%, 24.3% and 25.3%, respectively, but ultrasound had little change in ΔG value in the temperature range of 293-323 K. In conclusion, MPU pretreatment could remarkably enhance the enzymolysis of CGM, and this method can be applied to protein proteolysis industry to produce peptides. Copyright © 2015 Elsevier B.V. All rights reserved.

  20. Seasonal variability in nitrate and phosphate uptake kinetics in a forested headwater stream using pulse nutrient additions

    Science.gov (United States)

    Griffiths, N. A.; Mulholland, P. J.

    2011-12-01

    We used the Tracer Additions for Spiraling Curve Characterization (TASCC) approach to quantify seasonal variability in ambient nutrient spiraling metrics and nutrient uptake kinetics in the West Fork of Walker Branch, a forested headwater stream in eastern Tennessee, USA. We performed instantaneous additions of nitrate (NO3-) and phosphate (PO4-3) separately with a conservative tracer (chloride, Cl-) during the following biologically-important time periods: autumn (during leaf fall, high organic matter [OM] standing stocks), winter (low OM standing stocks), spring (prior to canopy closure), and summer (closed canopy). We predicted that nutrient demand would be highest during autumn and spring, as OM inputs fuel heterotrophic respiration and high light availability stimulates autotrophic production, respectively. The measured ambient PO4-3 uptake rates (Vf-amb) followed our predictions, with the highest Vf-amb rates in autumn (Vf-amb = 2.8 mm/min) and spring (Vf-amb = 2.9 mm/min), and undetectable uptake in winter. Further, maximum areal PO4-3 uptake rates (Umax) were higher in autumn (Umax = 297 μg/m2/min) than spring (Umax = 106 μg/m2/min), possibly due to greater nutrient demand of heterotrophs on leaf litter accumulations. Contrary to our predictions, ambient NO3- uptake rates were highest in autumn and winter (autumn: Vf-amb = 2.8 mm/min, winter: Vf-amb = 2.4 mm/min), and lowest in spring (Vf-amb = 1.0 mm/min). The higher than expected Vf-amb rate in winter may be due to higher stream metabolism rates and thus greater nitrogen demand; the lower than expected Vf-amb rate in spring may reflect an alleviation of nitrogen demand due to high ammonium concentrations during this time. As the demand for both nitrogen and phosphorus in Walker Branch is greatest in autumn, future work will characterize how nutrient metrics change during this dynamic time period (i.e., before, during, and after leaf fall).

  1. COMBINED THEORETICAL AND EXPERIMENTAL INVESTIGATION OF MECHANISMS AND KINETICS OF VAPOR-PHASE MERCURY UPTAKE BY CARBONACEOUS SURFACES; ANNUAL

    International Nuclear Information System (INIS)

    Radisav D. Vidic; Eric V. Borguet; Karl J. Johnson

    2000-01-01

    The overall goal of this research program is to gain fundamental understanding of the important chemistry and physics involved in mercury adsorption on carbonaceous surfaces. This knowledge will then be used to optimize adsorption processes and operating conditions to maximize the uptake of mercury within the required contact time. An additional long-term benefit of this research is the basic understanding of the Hg adsorption process, which may facilitate the design of new adsorbents for more efficient and cost-effective removal of Hg from a variety of effluent streams. Molecular modeling of the adsorption of Hg on carbonaceous surfaces will greatly increase the insight into the physics of the adsorption process and combined with in situ rate measurements of mercury adsorption and desorption (conventional and pulsed laser) on graphite using linear and nonlinear optical probes with real time optical resolution have the potential to provide fundamental insight into the process of mercury uptake by carbonaceous surfaces. Besides accurate assessment of key parameters influencing adsorption equilibrium, fundamental understanding of the kinetics of mercury adsorption, desorption, and diffusion will be developed in this study. These key physical and chemical processes postulated through molecular modeling efforts and verified by in situ measurements will be utilized to select (or develop) promising sorbents for mercury control, which will be tested under dynamic conditions using simulated flue gas

  2. Uptake and Loss Kinetics of 57Co, 85Sr and 134Cs on Blood Cockle Anadara granosa

    International Nuclear Information System (INIS)

    Srisuksawad, K; Prasertchiewchan, N.; Tungkitjanukij, S.; Pakkong, P.

    2005-02-01

    Adult blood cockle (A. granosa) were exposed in the laboratory to 57 Co, 85 Sr, and 134 Cs in seawater at average +- s.e. stable activities of 0.725+-0.010 Bq/ml, 0.917+-0.066 Bq/ml and 1.37+-0.105 Bq/ml, respectively. The study aims to determine key contaminant bioaccumulation, retention and loss parameters for bio-indicator organisms used in assessment of the impact of the effluent discharge from nuclear and non-nuclear facilities on coastal area. Natural coastal water conditions in dry season with a salinity of 30 ppt, at 30οC and p H 8.1+-0.1 of the study area (Bang Pa Kong river basin) were simulated as far as practicable. 19 d uptake of radiotracers showed that blood cockle did not accumulate 134 Cs and 85 Sr but considerably accumulated 57 Co. Non-linear regression model fitting of a 1-compartment exponential uptake model derived overall weight concentration factors for the whole cockle at saturation of 687.6+-6.23 ml/g for 57 Co. 22 d loss experiment showed that 57 Co is tightly bounded in blood cockle and 63.2+-15.2% retained in the whole body. Loss of 57 Co displayed 2-compartment loss kinetic. The calculated half time for the short and long components of loss model was estimated 1.4 dand 41 d, respectively

  3. Toxicological effects of multi-walled carbon nanotubes on Saccharomyces cerevisiae: The uptake kinetics and mechanisms and the toxic responses

    International Nuclear Information System (INIS)

    Zhu, Song; Zhu, Bin; Huang, Aiguo; Hu, Yang; Wang, Gaoxue; Ling, Fei

    2016-01-01

    Highlights: • MWCNTs ( 100 mg/L) had adverse effects on the cell proliferation. MWCNTs were clearly visible in lysosome, vacuole, endosome, mitochondria, multivesicular body and localization in the perinuclear region. The uptake kinetics data demonstrated that the maximum MWCNTs content (209.61 mg/g) was reached at 3 h, and a steady state was reached after 18 h. Based on the combined results of transmission electron microscope, endocytosis inhibition experiments and endocytosis-related genes (END3, END6, Sla2 and Rsp5) expression analysis, we elucidated MWCNTs uptake mechanism: (i) via a direct penetration of single MWCNTs; (ii) via endocytosis of single MWCNTs; and (iii) via endocytosis of MWCNTs aggregates. The percentage of apoptosis was significant increased at 600 mg/L. The decrease of mitochondrial transmembrane potential and the leakage of cytochrome c shown dose-dependent manners. Interestingly, there was no significant increase of reactive oxygen species (ROS). The apoptosis-related genes (SOD1, SOD2, Yca1, Nma111 and Nuc1) were significant changed. These results obtained in our study demonstrated that oxidized MWCNTs induce Saccharomyces cerevisiae apoptosis via mitochondrial impairment pathway.

  4. Microbial respiration and kinetics of extracellular enzymes activities through rhizosphere and detritusphere at agricultural site

    Science.gov (United States)

    Löppmann, Sebastian; Blagodatskaya, Evgenia; Kuzyakov, Yakov

    2014-05-01

    Rhizosphere and detritusphere are soil microsites with very high resource availability for microorganisms affecting their biomass, composition and functions. In the rhizosphere low molecular compounds occur with root exudates and low available polymeric compounds, as belowground plant senescence. In detritusphere the substrate for decomposition is mainly a polymeric material of low availability. We hypothesized that microorganisms adapted to contrasting quality and availability of substrates in the rhizosphere and detritusphere are strongly different in affinity of hydrolytic enzymes responsible for decomposition of organic compounds. According to common ecological principles easily available substrates are quickly consumed by microorganisms with enzymes of low substrate affinity (i.e. r-strategists). The slow-growing K-strategists with enzymes of high substrate affinity are better adapted for growth on substrates of low availability. Estimation of affinity of enzyme systems to the substrate is based on Michaelis-Menten kinetics, reflecting the dependency of decomposition rates on substrate amount. As enzymes-mediated reactions are substrate-dependent, we further hypothesized that the largest differences in hydrolytic activity between the rhizosphere and detritusphere occur at substrate saturation and that these differences are smoothed with increasing limitation of substrate. Affected by substrate limitation, microbial species follow a certain adaptation strategy. To achieve different depth gradients of substrate availability 12 plots on an agricultural field were established in the north-west of Göttingen, Germany: 1) 4 plots planted with maize, reflecting lower substrate availability with depth; 2) 4 unplanted plots with maize litter input (0.8 kg m-2 dry maize residues), corresponding to detritusphere; 3) 4 bare fallow plots as control. Maize litter was grubbed homogenously into the soil at the first 5 cm to ensure comparable conditions for the herbivore and

  5. Kinetic of magnetic nanoparticles uptake evaluated by morphometry of mice peritoneal cells

    International Nuclear Information System (INIS)

    Silva, L.P.; Kuckelhaus, S.; Guedes, M.H.A.; Lacava, Z.G.M.; Tedesco, A.C.; Morais, P.C.; Azevedo, R.B.

    2005-01-01

    The development of magnetic fluids (MFs) has led to a wide range of new biomedical applications. Nevertheless, few studies have examined the kinetics of the magnetic nanoparticles (MNPs) internalization by phagocytes. In this study, we present morphometry as a method to quantify the cell surface covered by MNPs. The maximum cell surface covered by MNPs aggregates was 32.5% (8.5 min), 18.3% (24.1 min), and 18.0% (20.2 min) in DMSA, citric acid and dextran-coated MNPs, respectively. We concluded that the phagocytosis process of MNPs is strongly dependent upon the coating species

  6. New fluorescent bile acids: synthesis, chemical characterization, and disastereoselective uptake by Caco-2 cells of 3-deoxy 3-NBD-amino deoxycholic and ursodeoxycholic acid.

    Science.gov (United States)

    Májer, Ferenc; Salomon, Johanna J; Sharma, Ruchika; Etzbach, Simona V; Najib, Mohd Nadzri Mohd; Keaveny, Ray; Long, Aideen; Wang, Jun; Ehrhardt, Carsten; Gilmer, John F

    2012-03-01

    Deoxycholic acid (DCA), a secondary bile acid (BA), and ursodeoxycholic acid (UDCA), a tertiary BA, cause opposing effects in vivo and in cell suspensions. Fluorescent analogues of DCA and UDCA could help investigate important questions about their cellular interactions and distribution. We have prepared a set of isomeric 3α- and 3β-amino analogues of UDCA and DCA and derivatised these with the discrete fluorophore, 4-nitrobenzo-2-oxa-1,3-diazol (NBD), forming the corresponding four fluorescent adducts. These absorb in the range 465-470 nm and fluoresce at approx. 535 nm. In order to determine the ability of the new fluorescent bile acids to mimic the parents, their uptake was studied using monolayers of Caco-2 cells, which are known to express multiple proteins of the organic anion-transporting peptide (OATP) subfamily of transporters. Cellular uptake was monitored over time at 4 and 37°C to distinguish between passive and active transport. All four BA analogues were taken up but in a strikingly stereo- and structure-specific manner, suggesting highly discriminatory interactions with transporter protein(s). The α-analogues of DCA and to a lesser extent UDCA were actively transported, whereas the β-analogues were not. The active transport process was saturable, with Michaelis-Menten constants for 3α-NBD DCA (5) being K(m)=42.27±12.98 μM and V(max)=2.8 ± 0.4 nmol/(mg protein*min) and for 3α-NBD UDCA (3) K(m)=28.20 ± 7.45 μM and V(max)=1.8 ± 0.2 nmol/(mg protein*min). These fluorescent bile acids are promising agents for investigating questions of bile acid biology and for detection of bile acids and related organic anion transport processes. Copyright © 2012 Elsevier Ltd. All rights reserved.

  7. Effect of pulsed electric field treatment on enzyme kinetics and thermostability of endogenous ascorbic acid oxidase in carrots (Daucus carota cv. Nantes).

    Science.gov (United States)

    Leong, Sze Ying; Oey, Indrawati

    2014-03-01

    The objective of this research was to study the enzyme kinetics and thermostability of endogenous ascorbic acid oxidase (AAO) in carrot purée (Daucus carota cv. Nantes) after being treated with pulsed electric field (PEF) processing. Various PEF treatments using electric field strength between 0.2 and 1.2kV/cm and pulsed electrical energy between 1 and 520kJ/kg were conducted. The enzyme kinetics and the kinetics of AAO thermal inactivation (55-70°C) were described using Michaelis-Menten model and first order reaction model, respectively. Overall, the estimated Vmax and KM values were situated in the same order of magnitude as the untreated carrot purée after being exposed to pulsed electrical energy between 1 and 400kJ/kg, but slightly changed at pulsed electrical energy above 500kJ/kg. However, AAO presented different thermostability depending on the electric field strength applied. After PEF treatment at the electric field strength between 0.2 and 0.5kV/cm, AAO became thermolabile (i.e. increase in inactivation rate (k value) at reference temperature) but the temperature dependence of k value (Ea value) for AAO inactivation in carrot purée decreased, indicating that the changes in k values were less temperature dependent. It is obvious that PEF treatment affects the temperature stability of endogenous AAO. The changes in enzyme kinetics and thermostability of AAO in carrot purée could be related to the resulting carrot purée composition, alteration in intracellular environment and the effective concentration of AAO released after being subjected to PEF treatment. Copyright © 2013 Elsevier Ltd. All rights reserved.

  8. Fitness Level and Not Aging per se, Determines the Oxygen Uptake Kinetics Response

    Directory of Open Access Journals (Sweden)

    Mitchell A. George

    2018-03-01

    Full Text Available Although aging has been associated to slower V˙O2 kinetics, some evidence indicates that fitness status and not aging per se might modulate this response. The main goal of this study was to examine the V˙O2, deoxygenated hemoglobin+myoglobin (deoxy-[Hb+Mb] kinetics, and the NIRS-derived vascular reperfusion responses in older compared to young men of different training levels (i.e., inactive, recreationally active, and endurance trained. Ten young inactive [YI; 26 ± 5 yrs.; peak V˙O2 (V˙O2peak, 2.96 ± 0.55 L·min−1], 10 young recreationally active (YR; 26 ± 6 yrs.; 3.92 ± 0.33 L·min−1, 10 young endurance trained (YT; 30 ± 4 yrs.; 4.42 ± 0.32 L·min−1, 7 older inactive (OI; 69 ± 4 yrs.; 2.50 ± 0.31 L·min−1, 10 older recreationally active (OR; 69 ± 5 yrs.; 2.71 ± 0.42 L·min−1, and 10 older endurance trained (OT; 66 ± 3 yrs.; 3.20 ± 0.35 L·min−1 men completed transitions of moderate intensity cycling exercise (MODS to determine V˙O2 and deoxy-[Hb+Mb] kinetics, and the deoxy-[Hb+Mb]/V˙O2 ratio. The time constant of V˙O2 (τV˙O2 was greater in YI (38.8 ± 10.4 s and OI (44.1 ± 10.8 s compared with YR (26.8 ± 7.5 s and OR (26.6 ± 6.5 s, as well as compared to YT (14.8 ± 3.4 s, and OT (17.7 ± 2.7 s (p < 0.05. τV˙O2 was greater in YR and OR compared with YT and OT (p < 0.05. The deoxy-[Hb+Mb]/V˙O2 ratio was greater in YI (1.23 ± 0.05 and OI (1.29 ± 0.08 compared with YR (1.11 ± 0.03 and OR (1.13 ± 0.06, as well as compared to YT (1.01 ± 0.03, and OT (1.06 ± 0.03 (p < 0.05. Similarly, the deoxy-[Hb+Mb]/ V˙O2 ratio was greater in YR and OR compared with YT and OT (p < 0.05. There was a main effect of training (p = 0.033, whereby inactive (p = 0.018 and recreationally active men (p = 0.031 had significantly poorer vascular reperfusion than endurance trained men regardless of age. This study demonstrated not only that age-related slowing of V˙O2 kinetics can be eliminated in endurance trained individuals

  9. Prior exercise speeds pulmonary oxygen uptake kinetics and increases critical power during supine but not upright cycling.

    Science.gov (United States)

    Goulding, Richie P; Roche, Denise M; Marwood, Simon

    2017-09-01

    What is the central question of this study? Critical power (CP) represents the highest work rate for which a metabolic steady state is attainable. The physiological determinants of CP are unclear, but research suggests that CP might be related to the time constant of phase II oxygen uptake kinetics (τV̇O2). What is the main finding and its importance? We provide the first evidence that τV̇O2 is mechanistically related to CP. A reduction of τV̇O2 in the supine position was observed alongside a concomitant increase in CP. This effect may be contingent on measures of oxygen availability derived from near-infrared spectroscopy. Critical power (CP) is a fundamental parameter defining high-intensity exercise tolerance and is related to the time constant of phase II pulmonary oxygen uptake kinetics (τV̇O2). To test the hypothesis that this relationship is causal, we determined the impact of prior exercise ('priming') on CP and τV̇O2 in the upright and supine positions. Seventeen healthy men were assigned to either upright or supine exercise groups, whereby CP, τV̇O2 and muscle deoxyhaemoglobin kinetics (τ [HHb] ) were determined via constant-power tests to exhaustion at four work rates with (primed) and without (control) priming exercise at ∼31%Δ. During supine exercise, priming reduced τV̇O2 (control 54 ± 18 s versus primed 39 ± 11 s; P exercise had no effect on τV̇O2 (control 37 ± 12 s versus primed 35 ± 8 s; P = 0.82), τ [HHb] (control 10 ± 5 s versus primed 14 ± 10 s; P = 0.10) or CP (control 235 ± 42 W versus primed 232 ± 35 W; P = 0.57) during upright exercise. The concomitant reduction of τV̇O2 and increased CP following priming in the supine group, effects that were absent in the upright group, provide the first experimental evidence that τV̇O2 is mechanistically related to critical power. The increased τ [HHb+Mb] suggests that this effect was mediated, at least in part, by improved oxygen

  10. Polycaprolactone/maltodextrin nanocarrier for intracellular drug delivery: formulation, uptake mechanism, internalization kinetics, and subcellular localization.

    Science.gov (United States)

    Korang-Yeboah, Maxwell; Gorantla, Yamini; Paulos, Simon A; Sharma, Pankaj; Chaudhary, Jaideep; Palaniappan, Ravi

    2015-01-01

    Prostate cancer (PCa) disease progression is associated with significant changes in intracellular and extracellular proteins, intracellular signaling mechanism, and cancer cell phenotype. These changes may have direct impact on the cellular interactions with nanocarriers; hence, there is the need for a much-detailed understanding, as nanocarrier cellular internalization and intracellular sorting mechanism correlate directly with bioavailability and clinical efficacy. In this study, we report the differences in the rate and mechanism of cellular internalization of a biocompatible polycaprolactone (PCL)/maltodextrin (MD) nanocarrier system for intracellular drug delivery in LNCaP, PC3, and DU145 PCa cell lines. PCL/MD nanocarriers were designed and characterized. PCL/MD nanocarriers significantly increased the intracellular concentration of coumarin-6 and fluorescein isothiocyanate-labeled bovine serum albumin, a model hydrophobic and large molecule, respectively. Fluorescence microscopy and flow cytometry analysis revealed rapid internalization of the nanocarrier. The extent of nanocarrier cellular internalization correlated directly with cell line aggressiveness. PCL/MD internalization was highest in PC3 followed by DU145 and LNCaP, respectively. Uptake in all PCa cell lines was metabolically dependent. Extraction of endogenous cholesterol by methyl-β-cyclodextrin reduced uptake by 75%±4.53% in PC3, 64%±6.01% in LNCaP, and 50%±4.50% in DU145, indicating the involvement of endogenous cholesterol in cellular internalization. Internalization of the nanocarrier in LNCaP was mediated mainly by macropinocytosis and clathrin-independent pathways, while internalization in PC3 and DU145 involved clathrin-mediated endocytosis, clathrin-independent pathways, and macropinocytosis. Fluorescence microscopy showed a very diffused and non-compartmentalized subcellular localization of the PCL/MD nanocarriers with possible intranuclear localization and minor colocalization in

  11. Substrate and pH-Dependent Kinetic Profile of 3-Mercaptopropionate Dioxygenase from Pseudomonas aeruginosa.

    Science.gov (United States)

    Fellner, Matthias; Aloi, Sekotilani; Tchesnokov, Egor P; Wilbanks, Sigurd M; Jameson, Guy N L

    2016-03-08

    Thiol dioxygenases catalyze the synthesis of sulfinic acids in a range of organisms from bacteria to mammals. A thiol dioxygenase from the bacterium Pseudomonas aeruginosa oxidizes both 3-mercaptopropionic acid and cysteine, with a ∼70 fold preference for 3-mercaptopropionic acid over all pHs. This substrate reactivity is widened compared to other thiol dioxygenases and was exploited in this investigation of the residues important for activity. A simple model incorporating two protonation events was used to fit profiles of the Michaelis-Menten parameters determined at different pH values for both substrates. The pKs determined using plots of k(cat)/Km differ at low pH, but not in a way easily attributable to protonation of the substrate alone and share a common value at higher pH. Plots of k(cat) versus pH are also quite different at low pH showing the monoprotonated ES complexes with 3-mercaptopropionic acid and cysteine have different pKs. At higher pH, k(cat) decreases sigmoidally with a similar pK regardless of substrate. Loss of reactivity at high pH is attributed to deprotonation of tyrosine 159 and its influence on dioxygen binding. A mechanism is proposed by which deprotonation of tyrosine 159 both blocks oxygen binding and concomitantly promotes cystine formation. Finally, the role of tyrosine 159 was further probed by production of a G95C variant that is able to form a cysteine-tyrosine crosslink homologous to that found in mammalian cysteine dioxygenases. Activity of this variant is severely impaired. Crystallography shows that when un-crosslinked, the cysteine thiol excludes tyrosine 159 from its native position, while kinetic analysis shows that the thioether bond impairs reactivity of the crosslinked form.

  12. Purification, Kinetic, and Thermodynamic Characteristics of an Exo-polygalacturonase from Penicillium notatum with Industrial Perspective.

    Science.gov (United States)

    Amin, Faiza; Bhatti, Haq Nawaz; Bilal, Muhammad; Asgher, Muhammad

    2017-09-01

    An extracellular exo-polygalacturonase (exo-PG) produced by Penicillium notatum was purified (3.07-folds) by ammonium sulfate fractionation, ion exchange, and gel filtration chromatography. Two distinct isoforms of the enzyme, namely exo-PGI and exo-PGII, were identified during column purification with molecular weights of 85 and 20 kDa, respectively, on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme displayed its optimum activity at pH 6.0 and 50 °C and was found to be stable in the slightly acidic pH (ranging from 4.5 to 6.0). Michaelis-Menten parameters, i.e., K m (app) and V max for pectin hydrolysis, were calculated to be 16.6 mg/mL and 20 μmol/mL/min, respectively. The enzyme followed biphasic deactivation kinetics. Phase I of the exo-PGI showed half-lives of 6.83 and 2.39 min at 55 and 80 °C, respectively, whereas phase II of the enzyme exhibited a half-life of 63.57 and 22.72 min at 55 and 80 °C, respectively. The activation energy for denaturation was 51.66 and 44.06 kJ/mol for phase I and phase II of the exo-PGI, respectively. The enzyme activity was considerably enhanced by Mn 2+ , whereas exposure to a hydrophobic environment (urea and sodium azide solution) drastically suppressed the enzyme activity. Results suggest that exo-PGI might be considered as a potential candidate for various applications, particularly in the food and textile industries.

  13. Microbial ureolysis in the seawater-catalysed urine phosphorus recovery system: Kinetic study and reactor verification.

    Science.gov (United States)

    Tang, Wen-Tao; Dai, Ji; Liu, Rulong; Chen, Guang-Hao

    2015-12-15

    Our previous study has confirmed the feasibility of using seawater as an economical precipitant for urine phosphorus (P) precipitation. However, we still understand very little about the ureolysis in the Seawater-based Urine Phosphorus Recovery (SUPR) system despite its being a crucial step for urine P recovery. In this study, batch experiments were conducted to investigate the kinetics of microbial ureolysis in the seawater-urine system. Indigenous bacteria from urine and seawater exhibited relatively low ureolytic activity, but they adapted quickly to the urine-seawater mixture during batch cultivation. During cultivation, both the abundance and specific ureolysis rate of the indigenous bacteria were greatly enhanced as confirmed by a biomass-dependent Michaelis-Menten model. The period for fully ureolysis was decreased from 180 h to 2.5 h after four cycles of cultivation. Based on the successful cultivation, a lab-scale SUPR reactor was set up to verify the fast ureolysis and efficient P recovery in the SUPR system. Nearly complete urine P removal was achieved in the reactor in 6 h without adding any chemicals. Terminal Restriction Fragment Length Polymorphism (TRFLP) analysis revealed that the predominant groups of bacteria in the SUPR reactor likely originated from seawater rather than urine. Moreover, batch tests confirmed the high ureolysis rates and high phosphorus removal efficiency induced by cultivated bacteria in the SUPR reactor under seawater-to-urine mixing ratios ranging from 1:1 to 9:1. This study has proved that the enrichment of indigenous bacteria in the SUPR system can lead to sufficient ureolytic activity for phosphate precipitation, thus providing an efficient and economical method for urine P recovery. Copyright © 2015 Elsevier Ltd. All rights reserved.

  14. Organic N cycling in Arctic ecosystems: Quantifying root uptake kinetics and temporal variability of soil amino acids.

    Science.gov (United States)

    Homyak, P. M.; Iverson, S. L.; Slessarev, E.; Marchus, K.; Schimel, J.

    2017-12-01

    Arctic ecosystems are undergoing shifts in plant community composition with increased warming. How these changes may alter ecosystem function is not well constrained, owing in part to uncertainties on how plant-soil feedbacks influence nutrient cycling. For nitrogen (N), in particular, understanding how these feedbacks may alter cycling rates is challenging because i) Arctic plants take up organic N (i.e., amino acids; AA) when inorganic N is limiting, yet ii) it has never been quantified, for any plant species growing in the wild, how much of its N demand is actually met by taking up AA. To advance fundamental understanding of plant-soil feedbacks as the Arctic warms, we are integrating field measurements of AA availability in N-limited tussock tundra (E. vaginatum) and a comparably less N-limited birch shrub tundra (Betula nana and Salix spp.) with a root uptake model. We used soil microdialysis to determine available AA concentrations in the soil solution and potential rates of AA diffusion and mass flow to roots at the Toolik Field Station in Alaska. These measurements are being combined with AA root uptake kinetic experiments using E. vaginatum to establish actual AA root uptake rates. We found that in the early growing season (June), total AA concentrations in the soil solution averaged 104 µg N L-1 and were similar to NH4+ across sites. In the late growing season (August), AA were the dominant form of N averaging 75 µg N L-1 while NH4+ decreased to 13 µg N L-1. In the early growing season AA diffusion rates in the soil averaged 200 ng N cm-2 s-1 and declined to 150 ng N cm-2 s-1 in the late growing season. Lysine, serine, and arginine were the most abundant AA and differences in the N status of sites did not affect total AA concentrations. Amino acids made up at least half of the N diffusing through the soil solution, suggesting they can subsidize the N demand of arctic plants. Ongoing field experiments at Toolik will be used to constrain actual AA root

  15. Locomotor muscle fatigue does not alter oxygen uptake kinetics during high-intensity exercise

    Directory of Open Access Journals (Sweden)

    James Hopker

    2016-10-01

    Full Text Available The slow component (VO2sc that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre fatigue condition or rest for 33 minutes (control condition according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-second maximal sprints at a fixed pedaling cadence of 90 rev·min-1. Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and VO2max determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue (P = 0.03, the VO2sc was not significantly different between the pre fatigue (464 ± 301 mL·min-1 and the control (556 ± 223 mL·min-1 condition (P = 0.50. Blood lactate response was not significantly different between conditions (P = 0.48 but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition (P < 0.01 suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the VO2 kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the VO2sc is strongly associated with locomotor muscle fatigue.

  16. Locomotor Muscle Fatigue Does Not Alter Oxygen Uptake Kinetics during High-Intensity Exercise.

    Science.gov (United States)

    Hopker, James G; Caporaso, Giuseppe; Azzalin, Andrea; Carpenter, Roger; Marcora, Samuele M

    2016-01-01

    The [Formula: see text] slow component ([Formula: see text]) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min -1 . Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and [Formula: see text] determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue ( P = 0.03), the [Formula: see text] was not significantly different between the pre-fatigue (464 ± 301 mL·min -1 ) and the control (556 ± 223 mL·min -1 ) condition ( P = 0.50). Blood lactate response was not significantly different between conditions ( P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition ( P locomotor muscle fatigue does not significantly alter the [Formula: see text] kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the [Formula: see text] is strongly associated with locomotor muscle fatigue.

  17. A KDE-Based Random Walk Method for Modeling Reactive Transport With Complex Kinetics in Porous Media

    Science.gov (United States)

    Sole-Mari, Guillem; Fernà ndez-Garcia, Daniel; Rodríguez-Escales, Paula; Sanchez-Vila, Xavier

    2017-11-01

    In recent years, a large body of the literature has been devoted to study reactive transport of solutes in porous media based on pure Lagrangian formulations. Such approaches have also been extended to accommodate second-order bimolecular reactions, in which the reaction rate is proportional to the concentrations of the reactants. Rather, in some cases, chemical reactions involving two reactants follow more complicated rate laws. Some examples are (1) reaction rate laws written in terms of powers of concentrations, (2) redox reactions incorporating a limiting term (e.g., Michaelis-Menten), or (3) any reaction where the activity coefficients vary with the concentration of the reactants, just to name a few. We provide a methodology to account for complex kinetic bimolecular reactions in a fully Lagrangian framework where each particle represents a fraction of the total mass of a specific solute. The method, built as an extension to the second-order case, is based on the concept of optimal Kernel Density Estimator, which allows the concentrations to be written in terms of particle locations, hence transferring the concept of reaction rate to that of particle location distribution. By doing so, we can update the probability of particles reacting without the need to fully reconstruct the concentration maps. The performance and convergence of the method is tested for several illustrative examples that simulate the Advection-Dispersion-Reaction Equation in a 1-D homogeneous column. Finally, a 2-D application example is presented evaluating the need of fully describing non-bilinear chemical kinetics in a randomly heterogeneous porous medium.

  18. Deciphering relationships between in-stream travel times, nutrient concentrations, and uptake through analysis of hysteretic and non-hysteretic kinetic behavior

    Science.gov (United States)

    Covino, T. P.; Bowden, W. B.; Gooseff, M. N.; Wollheim, W. M.; McGlynn, B. L.; Whittinghill, K. A.; Wlostowski, A. N.; Herstand, M. R.

    2012-12-01

    Understanding the relationship between solute travel time, concentration, and nutrient uptake remains a central question in watershed hydrology and biogeochemistry. Theoretical understanding predicts that nutrient uptake should increase as in-stream solute travel time lengthens and/or as concentration increases; however, results from field-based studies have been contradictory. We used a newly developed approach, Tracer Additions for Spiraling Curve Characterization (TASCC), to investigate relationships between solute travel time, nutrient concentration, and nutrient uptake across a range of stream types. This approach allows us to quantify in-stream nutrient uptake across a range of travel times and nutrient concentrations using single instantaneous injections (slugs) of conservative and non-conservative tracers. In some systems we observed counter-clockwise hysteresis loops in the relationship between nutrient uptake and concentration. Greater nutrient uptake on the falling limb of tracer breakthrough curves indicates stronger uptake for a given concentration at longer travel times. However, in other systems we did not observe hysteresis in these relationships. Lack of hysteresis indicates that nutrient uptake kinetics were not influenced by travel time travel time. Here we investigate the potential roles of travel time and in-stream flowpaths that could be responsible for hysteretic behavior.

  19. Comparison of the oxygen uptake kinetics of club and olympic champion rowers.

    Science.gov (United States)

    Ingham, Stephen A; Carter, Helen; Whyte, Gregory P; Doust, Jonathan H

    2007-05-01

    To test the hypothesis that elite rowers would possess a faster, more economic oxygen uptake response than club standard rowers. Eight Olympic champion (ELITE) rowers were compared with a cohort of eight club standard (CLUB) rowers. Participants completed a progressive exercise test to exhaustion, repeated 6-min moderate and heavy square-wave transitions, and a maximal 2000-m ergometer time trial. The time constant (tau) of the primary component (PC) was faster for the ELITE group compared with CLUB for moderate-intensity (13.9 vs 19.4 s, P = 0.02) and heavy-intensity (18.7 vs 22.4 s, P = 0.005) exercise. ELITE rowers consumed less oxygen for moderate (14.2 vs 15.6 mL x min(-1) x W(-1); P = 0.009) and heavy (12.1 vs 13.7 mL x min(-1) x W(-1); P = 0.01) exercise. A greater absolute slow component was observed in the ELITE group (P = 0.009), but no differences were noted when the slow component was expressed relative to work rate performed (P = 0.14). Intergroup correlation with time trial performance speed was significant for tauPC during heavy-intensity exercise (r = -0.59, P = 0.02). Compared with CLUB rowers, the shorter time constant response and greater economy observed in ELITE rowers may suggest advantageous adjustment of oxidative processes from rest to work. Training status or performance level do not seem to be associated with a smaller slow component when comparing CLUB and ELITE oarsmen.

  20. The uptake kinetics and immunotoxic effects of microcystin-LR in human and chicken peripheral blood lymphocytes in vitro

    International Nuclear Information System (INIS)

    Lankoff, Anna; Carmichael, Wayne W.; Grasman, Keith A.; Yuan, Moucun

    2004-01-01

    Microcystin-LR is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. We investigated the influence of this toxin on human and chicken immune system modulation in vitro. Peripheral blood lymphocytes were treated with microcystin-LR at environmentally relevant doses of 1, 10 and 25 μg/ml for 12, 24, 48, 72 h (for proliferation assay cells were treated for 72 h). T-cell and B-cell proliferation as well as apoptosis and necrosis were determined in human and chicken samples. IL-2 and IL-6 production by human lymphocytes also was measured. In addition, uptake kinetics of microcystin-LR into human and chicken peripheral blood lymphocytes were calculated by Liquid Chromatography (LS) /Mass Spectrometry (MS) analysis. At the highest dose microcystin-LR decreased T-cell proliferation and all doses of microcystin-LR inhibited B-cell proliferation. The frequency of apoptotic and necrotic cells increased in a dose and time-dependent manner. Human lymphocytes responded to stimulation with microcystin-LR by increased production of IL-6 and decreased production of IL-2. Human lymphocytes were able to uptake from 0.014 to 1.663 μg/ml and chicken lymphocytes from 0.035 to 1.733 μg/ml of the microcystin-LR added to the cultures, depending on the treatment time and dose. In conclusion, microcystin-LR acted as an immunomodulator in cytokine production and down-regulated lymphocyte functions by induction of apoptosis and necrosis. However, further studies dealing with the influence of microcystin-LR on expression cytokine genes and transcription factors are necessary to confirm these hypotheses

  1. Time Trials Versus Time-to-Exhaustion Tests: Effects on Critical Power, W', and Oxygen-Uptake Kinetics.

    Science.gov (United States)

    Karsten, Bettina; Baker, Jonathan; Naclerio, Fernando; Klose, Andreas; Bianco, Antonino; Nimmerichter, Alfred

    2018-02-01

    To investigate single-day time-to-exhaustion (TTE) and time-trial (TT) -based laboratory tests values of critical power (CP), W prime (W'), and respective oxygen-uptake-kinetic responses. Twelve cyclists performed a maximal ramp test followed by 3 TTE and 3 TT efforts interspersed by 60 min recovery between efforts. Oxygen uptake ( V ˙ O 2 ) was measured during all trials. The mean response time was calculated as a description of the overall [Formula: see text]-kinetic response from the onset to 2 min of exercise. TTE-determined CP was 279 ± 52 W, and TT-determined CP was 276 ± 50 W (P = .237). Values of W' were 14.3 ± 3.4 kJ (TTE W') and 16.5 ± 4.2 kJ (TT W') (P = .028). While a high level of agreement (-12 to 17 W) and a low prediction error of 2.7% were established for CP, for W' limits of agreements were markedly lower (-8 to 3.7 kJ), with a prediction error of 18.8%. The mean standard error for TTE CP values was significantly higher than that for TT CP values (2.4% ± 1.9% vs 1.2% ± 0.7% W). The standard errors for TTE W' and TT W' were 11.2% ± 8.1% and 5.6% ± 3.6%, respectively. The [Formula: see text] response was significantly faster during TT (~22 s) than TTE (~28 s). The TT protocol with a 60-min recovery period offers a valid, time-saving, and less error-filled alternative to conventional and more recent testing methods. Results, however, cannot be transferred to W'.

  2. Uptake, transfer and elimination kinetics of paralytic shellfish toxins in common octopus (Octopus vulgaris).

    Science.gov (United States)

    Lopes, Vanessa M; Baptista, Miguel; Repolho, Tiago; Rosa, Rui; Costa, Pedro Reis

    2014-01-01

    Marine phycotoxins derived from harmful algal blooms are known to be associated with mass mortalities in the higher trophic levels of marine food webs. Bivalve mollusks and planktivorous fish are the most studied vectors of marine phycotoxins. However, field surveys recently showed that cephalopod mollusks also constitute potential vectors of toxins. Thus, here we determine, for the first time, the time course of accumulation and depuration of paralytic shellfish toxins (PSTs) in the common octopus (Octopus vulgaris). Concomitantly, the underlying kinetics of toxin transfer between tissue compartments was also calculated. Naturally contaminated clams were used to orally expose the octopus to PSTs during 6 days. Afterwards, octopus specimens were fed with non-contaminated shellfish during 10 days of depuration period. Toxins reached the highest concentrations in the digestive gland surpassing the levels in the kidney by three orders of magnitude. PSTs were not detected in any other tissue analyzed. Net accumulation efficiencies of 42% for GTX5, 36% for dcSTX and 23% for C1+2 were calculated for the digestive gland. These compounds were the most abundant toxins in both digestive gland and the contaminated shellfish diet. The small differences in relative abundance of each toxin observed between the prey and the cephalopod predator indicates low conversion rates of these toxins. The depuration period was better described using an exponential decay model comprising a single compartment - the entire viscera. It is worth noting that since octopuses' excretion and depuration rates are low, the digestive gland is able to accumulate very high toxin concentrations for long periods of time. Therefore, the present study clearly shows that O. vulgaris is a high-potential vector of PSTs during and even after the occurrence of these toxic algal blooms. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change

    Directory of Open Access Journals (Sweden)

    I. J. George

    2007-08-01

    Full Text Available The kinetics and reaction mechanism for the heterogeneous oxidation of saturated organic aerosols by gas-phase OH radicals were investigated under NOx-free conditions. The reaction of 150 nm diameter Bis(2-ethylhexyl sebacate (BES particles with OH was studied as a proxy for chemical aging of atmospheric aerosols containing saturated organic matter. An aerosol reactor flow tube combined with an Aerodyne time-of-flight aerosol mass spectrometer (ToF-AMS and scanning mobility particle sizer (SMPS was used to study this system. Hydroxyl radicals were produced by 254 nm photolysis of O3 in the presence of water vapour. The kinetics of the heterogeneous oxidation of the BES particles was studied by monitoring the loss of a mass fragment of BES with the ToF-AMS as a function of OH exposure. We measured an initial OH uptake coefficient of γ0=1.3 (±0.4, confirming that this reaction is highly efficient. The density of BES particles increased by up to 20% of the original BES particle density at the highest OH exposure studied, consistent with the particle becoming more oxidized. Electrospray ionization mass spectrometry analysis showed that the major particle-phase reaction products are multifunctional carbonyls and alcohols with higher molecular weights than the starting material. Volatilization of oxidation products accounted for a maximum of 17% decrease of the particle volume at the highest OH exposure studied. Tropospheric organic aerosols will become more oxidized from heterogeneous photochemical oxidation, which may affect not only their physical and chemical properties, but also their hygroscopicity and cloud nucleation activity.

  4. Cs-134 transfer from water or food to the Ciprinid Tinca tinca Linnaeus: uptake and loss kinetics

    International Nuclear Information System (INIS)

    Corisco, J.A.G.; Carreiro, M.C.V.

    1991-01-01

    Experiments with 134 Cs and the fish Tinca tinca Linnaeus (fam. Cyprinidae), as a part of a more extensive work, concerning a simplified freshwater trophic chain using water from Fratel dam, (at Tejo River), were undertaken. Direct uptake from water, during a period of about 30 days, leads to a kinetics expressed by the power function: CF (t) = 0.58 t 0.781 (t in days), the concentration factor (CF) referred to wet weight. Retention study, showed the existence of two biological half-lives, Tb 1 = 7 days and Tb 2 = 87 days, which might concern respectively, the 134 Cs desorption from the transit organs and the loss of the assimilated isotope from the storage organs. In the accumulation through the food chain, using planktonic crustacean Daphnia magna Straus (Cladocera) as prey, a transfer factor (TF) related to wet weight of both fish and prey, is estimated through the power function: TF (t) = 0.022 t 0.578 (t in days). Finally, the retention study following the food pathway contamination, stresses the existence of one long term component, with half-life Tb = 61 days. The transfer factor kinetics seems to point out to a rather slow process, leading to lower 134 Cs concentration values, than the contamination through the water. The loss of the assimilated 134 Cs, uptaken through both pathways, water or food, is a slow process. The longer biological half-life is very important in Radiological Protection, once it may be attributed to the radionuclide loss from the muscular mass. (author)

  5. Pulmonary O2 uptake and leg blood flow kinetics during moderate exercise are slowed by hyperventilation-induced hypocapnic alkalosis

    Science.gov (United States)

    Chin, Lisa M. K.; Heigenhauser, George J. F.; Paterson, Donald H.

    2010-01-01

    The effect of hyperventilation-induced hypocapnic alkalosis (Hypo) on the adjustment of pulmonary O2 uptake (V̇o2p) and leg femoral conduit artery (“bulk”) blood flow (LBF) during moderate-intensity exercise (Mod) was examined in eight young male adults. Subjects completed four to six repetitions of alternate-leg knee-extension exercise during normal breathing [Con; end-tidal partial pressure of CO2 (PetCO2) ∼40 mmHg] and sustained hyperventilation (Hypo; PetCO2 ∼20 mmHg). Increases in work rate were made instantaneously from baseline (3 W) to Mod (80% estimated lactate threshold). V̇o2p was measured breath by breath by mass spectrometry and volume turbine, and LBF (calculated from mean femoral artery blood velocity and femoral artery diameter) was measured simultaneously by Doppler ultrasound. Concentration changes of deoxy (Δ[HHb])-, oxy (Δ[O2Hb])-, and total hemoglobin-myoglobin (Δ[HbTot]) of the vastus lateralis muscle were measured continuously by near-infrared spectroscopy (NIRS). The kinetics of V̇o2p, LBF, and Δ[HHb] were modeled using a monoexponential equation by nonlinear regression. The time constants for the phase 2 V̇o2p (Hypo, 49 ± 26 s; Con, 28 ± 8 s) and LBF (Hypo, 46 ± 16 s; Con, 23 ± 6 s) were greater (P alkalosis is associated with slower convective (i.e., slowed femoral artery and microvascular blood flow) and diffusive (i.e., greater fractional O2 extraction for a given ΔV̇o2p) O2 delivery, which may contribute to the hyperventilation-induced slowing of V̇o2p (and muscle O2 utilization) kinetics. PMID:20339012

  6. Muscle glycogen reduction in man: relationship between surface EMG activity and oxygen uptake kinetics during heavy exercise.

    Science.gov (United States)

    Osborne, Mark A; Schneider, Donald A

    2006-01-01

    The purpose of this study was to determine whether muscle glycogen reduction prior to exercise would alter muscle fibre recruitment pattern and change either on-transient O2 uptake (VO2) kinetics or the VO2 slow component. Eight recreational cyclists (VO2peak, 55.6 +/- 1.3 ml kg (-1) min(-1)) were studied during 8 min of heavy constant-load cycling performed under control conditions (CON) and under conditions of reduced type I muscle glycogen content (GR). VO2 was measured breath-by-breath for the determination of VO2 kinetics using a double-exponential model with independent time delays. VO2 was higher in the GR trial compared to the CON trial as a result of augmented phase I and II amplitudes, with no difference between trials in the phase II time constant or the magnitude of the slow component. The mean power frequency (MPF) of electromyography activity for the vastus medialis increased over time during both trials, with a greater rate of increase observed in the GR trial compared to the CON trial. The results suggest that the recruitment of additional type II motor units contributed to the slow component in both trials. An increase in fat metabolism and augmented type II motor unit recruitment contributed to the higher VO2 in the GR trial. However, the greater rate of increase in the recruitment of type II motor units in the GR trial may not have been of sufficient magnitude to further elevate the slow component when VO2 was already high and approaching VO2peak .

  7. Bulk chlorine uptake by polyamide active layers of thin-film composite membranes upon exposure to free chlorine-kinetics, mechanisms, and modeling.

    Science.gov (United States)

    Powell, Joshua; Luh, Jeanne; Coronell, Orlando

    2014-01-01

    We studied the volume-averaged chlorine (Cl) uptake into the bulk region of the aromatic polyamide active layer of a reverse osmosis membrane upon exposure to free chlorine. Volume-averaged measurements were obtained using Rutherford backscattering spectrometry with samples prepared at a range of free chlorine concentrations, exposure times, and mixing, rinsing, and pH conditions. Our volume-averaged measurements complement previous studies that have quantified Cl uptake at the active layer surface (top ≈ 7 nm) and advance the mechanistic understanding of Cl uptake by aromatic polyamide active layers. Our results show that surface Cl uptake is representative of and underestimates volume-averaged Cl uptake under acidic conditions and alkaline conditions, respectively. Our results also support that (i) under acidic conditions, N-chlorination followed by Orton rearrangement is the dominant Cl uptake mechanism with N-chlorination as the rate-limiting step; (ii) under alkaline conditions, N-chlorination and dechlorination of N-chlorinated amide links by hydroxyl ion are the two dominant processes; and (iii) under neutral pH conditions, the rates of N-chlorination and Orton rearrangement are comparable. We propose a kinetic model that satisfactorily describes Cl uptake under acidic and alkaline conditions, with the largest discrepancies between model and experiment occurring under alkaline conditions at relatively high chlorine exposures.

  8. Inhibition of serotonin transport by (+)McN5652 is noncompetitive

    Energy Technology Data Exchange (ETDEWEB)

    Hummerich, Rene [Biochemical Laboratory, Central Institute of Mental Health, 68159 Mannheim (Germany); Schulze, Oliver [Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany); Raedler, Thomas [Department of Psychiatry and Psychotherapy, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany); Mikecz, Pal [Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany); Reimold, Matthias [Department of Nuclear Medicine, University Hospital Tuebingen, D-72076 Tuebingen (Germany); Brenner, Winfried [Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany); Clausen, Malte [Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany); Schloss, Patrick [Biochemical Laboratory, Central Institute of Mental Health, 68159 Mannheim (Germany); Buchert, Ralph [Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg (Germany)]. E-mail: buchert@uke.uni-hamburg.de

    2006-04-15

    Introduction: Imaging of the serotonergic innervation of the brain using positron emission tomography (PET) with the serotonin transporter (SERT) ligand [{sup 11C}] (+)McN5652 might be affected by serotonin in the synaptic cleft if there is relevant interaction between [{sup 11}C] (+)McN5652 and serotonin at the SERT. The aim of the present study therefore was to pharmacologically characterize the interaction of [{sup 11}C] (+)McN5652 and serotonin at the SERT. Methods: In vitro saturation analyses of [{sup 3}H]serotonin uptake into HEK293 cells stably expressing the human SERT were performed in the absence and presence of unlabelled (+)McN5652. Data were evaluated assuming Michaelis-Menten kinetics. Results: Unlabelled (+)McN5652 significantly reduced the maximal rate of serotonin transport V {sub max} of SERT without affecting the Michaelis-Menten constant K {sub M}. Conclusions: This finding indicates that (+)McN5652 inhibits serotonin transport through the SERT in a noncompetitive manner. This might suggest that [{sup 11}C] (+)McN5652 PET is not significantly affected by endogenous serotonin.

  9. Inhibition of serotonin transport by (+)McN5652 is noncompetitive

    International Nuclear Information System (INIS)

    Hummerich, Rene; Schulze, Oliver; Raedler, Thomas; Mikecz, Pal; Reimold, Matthias; Brenner, Winfried; Clausen, Malte; Schloss, Patrick; Buchert, Ralph

    2006-01-01

    Introduction: Imaging of the serotonergic innervation of the brain using positron emission tomography (PET) with the serotonin transporter (SERT) ligand [ 11C ] (+)McN5652 might be affected by serotonin in the synaptic cleft if there is relevant interaction between [ 11 C] (+)McN5652 and serotonin at the SERT. The aim of the present study therefore was to pharmacologically characterize the interaction of [ 11 C] (+)McN5652 and serotonin at the SERT. Methods: In vitro saturation analyses of [ 3 H]serotonin uptake into HEK293 cells stably expressing the human SERT were performed in the absence and presence of unlabelled (+)McN5652. Data were evaluated assuming Michaelis-Menten kinetics. Results: Unlabelled (+)McN5652 significantly reduced the maximal rate of serotonin transport V max of SERT without affecting the Michaelis-Menten constant K M . Conclusions: This finding indicates that (+)McN5652 inhibits serotonin transport through the SERT in a noncompetitive manner. This might suggest that [ 11 C] (+)McN5652 PET is not significantly affected by endogenous serotonin

  10. Characterization of hydroxybenzoic acid chelating resins: equilibrium, kinetics, and isotherm profiles for Cd(II and Pb(II uptake

    Directory of Open Access Journals (Sweden)

    BHAVNA A. SHAH

    2011-06-01

    Full Text Available Chelating ion-exchange resins were synthesized by polycondensation of ortho/para hydroxybenzoic acid with resorcinol/catechol employing formaldehyde as cross-linking agent at 80±5 °C in DMF. The resins were characterized by FTIR and XRD. The uptake behaviour of synthesized resins for Cd(II and Pb(II ions have been studied depending on contact time, pH, metal ion concentration and temperature. The sorption data obtained at optimized conditions were analyzed by the Langmuir and Freundlich isotherms. Experimental data of all metal–resin system were best represented by the Freundlich isotherm. The maximum obtained sorption capacity for cadmium was 69.53 mg g-1 and 169.32 mg g-1 for Lead. The adsorption process follows first order kinetics and the specific rate constant Kr was obtained by the application of the Lagergan equation. Thermodynamic parameters ∆Gads, ∆Sads and ∆Hads were calculated for the metal–resin systems. The external diffusion rate constant (KS and the intra-particle diffusion rate constant (Kid were calculated by the Spahn–Schlunder and Weber–Morris models, respectively. The sorption process was found to follow an intra-particle diffusion phenomenon.

  11. Reaction and catalyst engineering to exploit kinetically controlled whole-cell multistep biocatalysis for terminal FAME oxyfunctionalization.

    Science.gov (United States)

    Schrewe, Manfred; Julsing, Mattijs K; Lange, Kerstin; Czarnotta, Eik; Schmid, Andreas; Bühler, Bruno

    2014-09-01

    The oxyfunctionalization of unactivated C−H bonds can selectively and efficiently be catalyzed by oxygenase-containing whole-cell biocatalysts. Recombinant Escherichia coli W3110 containing the alkane monooxygenase AlkBGT and the outer membrane protein AlkL from Pseudomonas putida GPo1 have been shown to efficiently catalyze the terminal oxyfunctionalization of renewable fatty acid methyl esters yielding bifunctional products of interest for polymer synthesis. In this study, AlkBGTL-containing E. coli W3110 is shown to catalyze the multistep conversion of dodecanoic acid methyl ester (DAME) via terminal alcohol and aldehyde to the acid, exhibiting Michaelis-Menten-type kinetics for each reaction step. In two-liquid phase biotransformations, the product formation pattern was found to be controlled by DAME availability. Supplying DAME as bulk organic phase led to accumulation of the terminal alcohol as the predominant product. Limiting DAME availability via application of bis(2-ethylhexyl)phthalate (BEHP) as organic carrier solvent enabled almost exclusive acid accumulation. Furthermore, utilization of BEHP enhanced catalyst stability by reducing toxic effects of substrate and products. A further shift towards the overoxidized products was achieved by co-expression of the gene encoding the alcohol dehydrogenase AlkJ, which was shown to catalyze efficient and irreversible alcohol to aldehyde oxidation in vivo. With DAME as organic phase, the aldehyde accumulated as main product using resting cells containing AlkBGT, AlkL, as well as AlkJ. This study highlights the versatility of whole-cell biocatalysis for synthesis of industrially relevant bifunctional building blocks and demonstrates how integrated reaction and catalyst engineering can be implemented to control product formation patterns in biocatalytic multistep reactions. © 2014 Wiley Periodicals, Inc.

  12. Nitrous oxide production kinetics during nitrate reduction in river sediments.

    Science.gov (United States)

    Laverman, Anniet M; Garnier, Josette A; Mounier, Emmanuelle M; Roose-Amsaleg, Céline L

    2010-03-01

    A significant amount of nitrogen entering river basins is denitrified in riparian zones. The aim of this study was to evaluate the influence of nitrate and carbon concentrations on the kinetic parameters of nitrate reduction as well as nitrous oxide emissions in river sediments in a tributary of the Marne (the Seine basin, France). In order to determine these rates, we used flow-through reactors (FTRs) and slurry incubations; flow-through reactors allow determination of rates on intact sediment slices under controlled conditions compared to sediment homogenization in the often used slurry technique. Maximum nitrate reduction rates (R(m)) ranged between 3.0 and 7.1microg Ng(-1)h(-1), and affinity constant (K(m)) ranged from 7.4 to 30.7mg N-NO(3)(-)L(-1). These values were higher in slurry incubations with an R(m) of 37.9microg Ng(-1)h(-1) and a K(m) of 104mg N-NO(3)(-)L(-1). Nitrous oxide production rates did not follow Michaelis-Menten kinetics, and we deduced a rate constant with an average of 0.7 and 5.4ng Ng(-1)h(-1) for FTR and slurry experiments respectively. The addition of carbon (as acetate) showed that carbon was not limiting nitrate reduction rates in these sediments. Similar rates were obtained for FTR and slurries with carbon addition, confirming the hypothesis that homogenization increases rates due to release of and increasing access to carbon in slurries. Nitrous oxide production rates in FTR with carbon additions were low and represented less than 0.01% of the nitrate reduction rates and were even negligible in slurries. Maximum nitrate reduction rates revealed seasonality with high potential rates in fall and winter and low rates in late spring and summer. Under optimal conditions (anoxia, non-limiting nitrate and carbon), nitrous oxide emission rates were low, but significant (0.01% of the nitrate reduction rates). Copyright 2009 Elsevier Ltd. All rights reserved.

  13. Depuration and uptake kinetics of I, CS, MN, ZN and CD by the earthworm (lumbricus terrestris) in radiotracer-spiked litter

    International Nuclear Information System (INIS)

    Sheppard, S.C.; Evenden, W.G.; Cornwell, T.C.

    1997-01-01

    The relative depuration and uptake kinetics of contaminants should be known to interpret appropriately the use of organisms such as earthworms in environmental bioassays and monitoring. For example, 14-d earthworm bioassays should be interpreted with the knowledge that some contaminants will continue to accumulate in tissues for months. The radiotracers 125 I, 134 Cs, 54 Mn, 65 Zn, and 109 Cd were applied to deciduous litter and specimens of Lumbricus terrestris were exposed, either to litter alone or to litter on the top of soil columns. Depuration was monitored for 120 d and uptake, in a separate experiment, for 20 d. Both depuration and uptake were described using two-phase, first-order statistical models. Gut clearance had a mean half-time of 1.4 d. The mean half-time for physiological depuration decreased from I (210 d) > Cd (150 d) > Zn (69 d) > Mn (40 d) > Cs (24 d). Both the deputation and the uptake experiments were necessary to resolve even partially the multiphase processes. Earthworm/soil dry weight concentration ratios decreased from Cd > Zn > I ≥ Cs ≥ Mn. The very slow kinetics indicate that tissue concentrations will increase continuously for a long time, with important implications for subsequent food-chain transfers. (author)

  14. 18F-FLT uptake kinetics in head and neck squamous cell carcinoma: A PET imaging study

    International Nuclear Information System (INIS)

    Liu, Dan; Fenwick, John D.; Chalkidou, Anastasia; Landau, David B.; Marsden, Paul K.

    2014-01-01

    Purpose: To analyze the kinetics of 3 ′ -deoxy-3 ′ -[F-18]-fluorothymidine (18F-FLT) uptake by head and neck squamous cell carcinomas and involved nodes imaged using positron emission tomography (PET). Methods: Two- and three-tissue compartment models were fitted to 12 tumor time-activity-curves (TACs) obtained for 6 structures (tumors or involved nodes) imaged in ten dynamic PET studies of 1 h duration, carried out for five patients. The ability of the models to describe the data was assessed using a runs test, the Akaike information criterion (AIC) and leave-one-out cross-validation. To generate parametric maps the models were also fitted to TACs of individual voxels. Correlations between maps of different parameters were characterized using Pearson'sr coefficient; in particular the phosphorylation rate-constants k 3-2tiss and k 5 of the two- and three-tissue models were studied alongside the flux parameters K FLT-2tiss and K FLT of these models, and standardized uptake values (SUV). A methodology based on expectation-maximization clustering and the Bayesian information criterion (“EM-BIC clustering”) was used to distil the information from noisy parametric images. Results: Fits of two-tissue models 2C3K and 2C4K and three-tissue models 3C5K and 3C6K comprising three, four, five, and six rate-constants, respectively, pass the runs test for 4, 8, 10, and 11 of 12 tumor TACs. The three-tissue models have lower AIC and cross-validation scores for nine of the 12 tumors. Overall the 3C6K model has the lowest AIC and cross-validation scores and its fitted parameter values are of the same orders of magnitude as literature estimates. Maps ofK FLT and K FLT-2tiss are strongly correlated (r = 0.85) and also correlate closely with SUV maps (r = 0.72 for K FLT-2tiss , 0.64 for K FLT ). Phosphorylation rate-constant maps are moderately correlated with flux maps (r = 0.48 for k 3-2tiss vs K FLT-2tiss and r = 0.68 for k 5 vs K FLT ); however, neither phosphorylation

  15. Oxygen uptake kinetics during and after exercise are useful markers of coronary artery disease in patients with exercise electrocardiography suggesting myocardial ischemia

    International Nuclear Information System (INIS)

    Tajima, Akihiko; Ohkoshi, Nobuyuki; Kawara, Tokuhiro; Aizawa, Tadanori; Itoh, Haruki; Maeda, Tomoko; Osada, Naohiko; Omiya, Kazuto; Wasserman, K.

    2009-01-01

    The aim of the current study was to determine if the slowed exercise oxygen uptake (VO 2 ) kinetics, which is developed by myocardial ischemia, would be accompanied by delayed recovery VO 2 kinetics in patients with coronary artery disease (CAD). Thirty-seven patients with significant ST depression during treadmill exercise underwent cardiopulmonary exercise testing with cycle ergometer. Measurements performed are the ratios of change in increase in oxygen (O 2 ) uptake relative to increase in work rate (ΔVO 2 /ΔWR) across anaerobic threshold (AT) and 1 mm ST depression point (ST-dep), the time constants of VO 2 during recovery (T 1/2 VO 2 ), stress radio-isotope scintigraphy and coronary angiography. Patients were divided into CAD positive (CAD+) and CAD negative (CAD-) groups, based on coronary angiography. In CAD+, ΔVO 2 /ΔWR decreased above AT and ST-dep, in contrast to CAD- patients. The T 1/2 VO 2 in CAD+ (103.1±13.0 s) was greater than that of CAD- (76.5±8.7 s) and showed negative correlations to the ratios of ΔVO 2 /ΔWR across AT and ST-dep. These parameters improved in the patients who underwent coronary bypass surgery. Exercise and recovery VO 2 kinetics were slowed when myocardial ischemia was provoked by exercise. Measurement of exercise and recovery VO 2 kinetics improve the accuracy of the exercise electrocardiogram diagnosis of CAD. (author)

  16. Thermal and single frequency counter-current ultrasound pretreatments of sodium caseinate: enzymolysis kinetics and thermodynamics, amino acids composition, molecular weight distribution and antioxidant peptides.

    Science.gov (United States)

    Abdualrahman, Mohammed Adam Y; Ma, Haile; Zhou, Cunshan; Yagoub, Abu ElGasim A; Hu, Jiali; Yang, Xue

    2016-12-01

    Due to the disadvantages of traditional enzymolysis, pretreatments are crucial to enhance protein enzymolysis. Enzymolysis kinetics and thermodynamics, amino acids composition, molecular weight distribution, fluorescence spectroscopy and antioxidant activity of thermal (HT) and single frequency counter-current ultrasound (SCFU) pretreated sodium caseinate (NaCas) were studied. Enzymolysis of untreated NaCas (control) improved significantly (P < 0.05) by SFCU and followed by HT. Values of the Michaelis-Menten constant (K M ) of SFCU and HT were 0.0212 and 0.0250, respectively. HT and SFCU increased (P < 0.05) the reaction rate constant (k) by 38.64 and 90.91%, respectively at 298 K. k values decreased with increasing temperature. The initial activation energy (46.39 kJ mol -1 ) reduced (P < 0.05) by HT (39.66 kJ mol -1 ) and further by SFCU (33.42 kJ mol -1 ). SFCU-pretreated NaCas hydrolysates had the highest contents of hydrophobic, aromatic, positively and negatively charged amino acids. Medium-sized peptides (5000-1000 Da) are higher in SFCU (78.11%) than HT and the control. SFCU induced molecular unfolding of NaCas proteins. Accordingly, SFCU-pretreated NaCas hydrolysate exhibited the highest scavenging activity on DPPH and hydroxyl radicals, reducing power, and iron chelating ability. SFCU pretreatment would be a useful tool for production of bioactive peptides from NaCas hydrolysate. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

  17. Kinetics of 13N-ammonia uptake in myocardial single cells indicating potential limitations in its applicability as a marker of myocardial blood flow

    International Nuclear Information System (INIS)

    Rauch, B.; Helus, F.; Grunze, M.; Braunwell, E.; Mall, G.; Hasselbach, W.; Kuebler, W.

    1985-01-01

    To study kinetics and principles of cellular uptake of 13 N-ammonia, a marker of coronary perfusion in myocardial scintigraphy, heart muscle cells of adult rats were isolated by perfusion with collagenase and hyaluronidase. Net uptake of 13 N, measured by flow dialysis, reached equilibrium within 20 sec in the presence of sodium bicarbonate and carbon dioxide (pH 7.4, 37 degrees C). Total extraction, 80 sec after the reaction start, was 786 +/- 159 mumol/ml cell volume. Cells destroyed by calcium overload were unable to extract 13 N-ammonia. Omission of bicarbonate and carbon dioxide reduced total extraction to 36% of control. 13 N-Ammonia uptake could also be reduced by 50 muM 4,4' diisothiocyanostilbene 2,2' disulfonic acid, by 100 micrograms/ml 1-methionine sulfoximine, and by preincubation with 5 muM free oleic acid. These results indicate that in addition to metabolic trapping by glutamine synthetase, the extraction of 13 N-ammonia by myocardial cells is influenced by cell membrane integrity, intracellular-extracellular pH gradient, and possibly an anion exchange system for bicarbonate. For this reason, the uptake of 13 N-ammonia may not always provide a valid measurement of myocardial perfusion

  18. Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth, morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

    DEFF Research Database (Denmark)

    Jampeetong, Arunothai; Brix, Hans

    2009-01-01

    In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO3-, NH4+, or both at equimolar concentrations (500 μM). Plants supplied with only NO3- had lower growth rates (0.17 ± 0.01 g g-1 d-1), shorter roots, smaller...... leaves with less chlorophyll than plants supplied with NH4+ alone or in combination with NO3- (RGR = 0.28 ± 0.01 g g-1 d-1). Ammonium was the preferred form of N taken up. The maximal rate of NH4+ uptake (Vmax) was 6-14 times higher than the maximal uptake rate of NO3- and the minimum concentration...... for uptake (Cmin) was lower for NH4+ than for NO3-. Plants supplied with NO3- had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO3- was primarily reduced in the roots, but NRA levels were generally low (NH4...

  19. Kinetics of 3H-serotonin uptake by platelets in infantile autism and developmental language disorder (including five pairs of twins)

    International Nuclear Information System (INIS)

    Katsui, T.; Okuda, M.; Usuda, S.; Koizumi, T.

    1986-01-01

    The kinetics of 5-HT uptake by platelets was studied in cases of infantile autism and developmental language disorder (DLD) and normal subjects. Two patients of the autism group were twins, and the seven patients of the DLD group were members of four pairs of twins. The Vmax values (means +/- SD) for autism and DLD were 6.46 +/- .90 pmol 5-HT/10(7) cells/min and 4.85 +/- 1.50 pmol 5-HT/10(7) cells/min, respectively. These values were both significantly higher than that of 2.25 +/- .97 pmole 5-HT/10(7) cells/min for normal children. The Km values of the three groups were not significantly different. Data on the five pairs of twins examined suggested that the elevated Vmax of 5-HT uptake by platelets was determined genetically

  20. Kinetics of 3H-serotonin uptake by platelets in infantile autism and developmental language disorder (including five pairs of twins)

    Energy Technology Data Exchange (ETDEWEB)

    Katsui, T.; Okuda, M.; Usuda, S.; Koizumi, T.

    1986-03-01

    The kinetics of 5-HT uptake by platelets was studied in cases of infantile autism and developmental language disorder (DLD) and normal subjects. Two patients of the autism group were twins, and the seven patients of the DLD group were members of four pairs of twins. The Vmax values (means +/- SD) for autism and DLD were 6.46 +/- .90 pmol 5-HT/10(7) cells/min and 4.85 +/- 1.50 pmol 5-HT/10(7) cells/min, respectively. These values were both significantly higher than that of 2.25 +/- .97 pmole 5-HT/10(7) cells/min for normal children. The Km values of the three groups were not significantly different. Data on the five pairs of twins examined suggested that the elevated Vmax of 5-HT uptake by platelets was determined genetically.

  1. Tracking of cell nuclei for assessment of in vitro uptake kinetics in ultrasound-mediated drug delivery using fibered confocal fluorescence microscopy.

    Science.gov (United States)

    Derieppe, Marc; de Senneville, Baudouin Denis; Kuijf, Hugo; Moonen, Chrit; Bos, Clemens

    2014-10-01

    Previously, we demonstrated the feasibility to monitor ultrasound-mediated uptake of a cell-impermeable model drug in real time with fibered confocal fluorescence microscopy. Here, we present a complete post-processing methodology, which corrects for cell displacements, to improve the accuracy of pharmacokinetic parameter estimation. Nucleus detection was performed based on the radial symmetry transform algorithm. Cell tracking used an iterative closest point approach. Pharmacokinetic parameters were calculated by fitting a two-compartment model to the time-intensity curves of individual cells. Cells were tracked successfully, improving time-intensity curve accuracy and pharmacokinetic parameter estimation. With tracking, 93 % of the 370 nuclei showed a fluorescence signal variation that was well-described by a two-compartment model. In addition, parameter distributions were narrower, thus increasing precision. Dedicated image analysis was implemented and enabled studying ultrasound-mediated model drug uptake kinetics in hundreds of cells per experiment, using fiber-based confocal fluorescence microscopy.

  2. Basic microscopic theory of the distribution, transfer and uptake kinetics of dissolved radionuclides by suspended particulate matter - Part I; Theory development

    International Nuclear Information System (INIS)

    Abril, J.M.

    1998-01-01

    Recently much experimental effort has been focused on determining those factors which affect the kinetics and the final equilibrium conditions for the uptake of radionuclides from the aqueous phase by particulate matter. At present, some of these results appear to be either surprising or contradictory and introduce some uncertainty in which parameter values are most appropriate for environmental modelling. In this paper, we study the ionic exchange between the dissolved phase and suspended particles from a microscopic viewpoint, developing a mathematical description of the kinetic transfer and the k d distribution coefficients. The most relevant contribution is the assumption that the exchange of radionuclides occurs in a specific surface layer on the particles, with a non-zero thickness. A wide range of experimental findings can be explained with this theory. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

  3. [{sup 14}C]Serotonin uptake and [O-methyl-{sup 11}C]venlafaxine kinetics in porcine brain

    Energy Technology Data Exchange (ETDEWEB)

    Smith, D.F. E-mail: dfsmith@inet.uni2.dk; Hansen, S.B.; Oestergaard, L.; Gee, A.D.; Danielsen, E.; Ishizu, K.; Bender, D.; Poulsen, P.H.; Gjedde, A

    2001-08-01

    As part of our program of developing PET tracers for neuroimaging of psychotropic compounds, venlafaxine, an antidepressant drug, was evaluated. First, we measured in vitro rates of serotonin uptake in synaptosomes prepared from selected regions of porcine brain. Then, we determined the pharmacokinetics of venlafaxine, [O-methyl-{sup 11}C]-labeled for PET. Synaptosomal studies showed that the active uptake of [{sup 14}C]5-HT differed markedly between brain regions, with highest rates in hypothalamus, raphe region, and thalamus, and lowest rates in cortex and cerebellum. PET studies showed that the unidirectional rate of uptake of [O-methyl-{sup 11}C]venlafaxine from blood to brain was highest in the hypothalamus, raphe region, thalamus and basal ganglia and lowest in the cortex and cerebellum. Under normal physiological conditions, the capillary permeability-surface area (PS) product for [O-methyl-{sup 11}C]venlafaxine could not be estimated, because of complete flow-limitation of the cerebral uptake. Nevertheless, a correlation occurred between the apparent partition volume of the radiotracer and the rate of active uptake of 5-HT in selected regions of the porcine brain. During hypercapnia, limitations of blood-brain transfer were observed, giving PS-products for water that were only ca. 50% higher than those of venlafaxine. Thus, under normal physiological conditions, the rate of uptake of venlafaxine from blood into brain is completely flow-limited.

  4. Kinetics of caesium and potassium absorption by roots of three grass pastures and competitive effects of potassium on caesium uptake in Cynodon sp.

    Science.gov (United States)

    Ayub, J. Juri; Valverde, L. Rubio; Garcia-Sanchez, M. J.; Fernandez, J. A.; Velasco, R. H.

    2008-08-01

    Caesium uptake by plant roots has been normally associated with the uptake of potassium as the potassium transport systems present in plants have also the capacity to transport caesium. Three grass species (Eragrostis curvula, Cynodon sp and Distichlis spicata) growing in seminatural grassland of central Argentina were selected to study their capability to incorporate Cs+ (and K+) using electrophysiological techniques. Although the 137Cs soil inventory ranged between 328-730 Bq m-2 in this region, no 137Cs activity was detected in these plants. However, all the species, submitted previously to K+ starvation, showed the uptake of both Cs+ and K+ when micromolar concentrations of these cations were present in the medium. The uptake showed saturation kinetics for both cations that could be fitted to the Michelis-Menten model. KM values were smaller for K+ than for Cs+, indicating a higher affinity for the first cation. The presence of increasing K+ concentrations in the assay medium inhibited Cs+ uptake in Cynodon sp., as expected if both cations are transported by the same transport systems. This effect is due to the competition of both ions for the union sites of the high affinity potassium transporters. In field situation, where soil concentration of Cs+ is smaller than K+ concentration, is then expectable that caesium activity in plants is not detectable. Nevertheless, the studied plants would have the capacity to incorporate caesium if its availability in soil solution increases. In addition, studies of Cs/K interaction can help us to understand the variability in transfer factors.

  5. Kinetics of caesium and potassium absorption by roots of three grass pastures and competitive effects of potassium on caesium uptake in Cynodon sp

    International Nuclear Information System (INIS)

    Ayub, J. Juri; Velasco, R. H.; Valverde, L. Rubio; Garcia-Sanchez, M. J.; Fernandez, J. A.

    2008-01-01

    Caesium uptake by plant roots has been normally associated with the uptake of potassium as the potassium transport systems present in plants have also the capacity to transport caesium. Three grass species (Eragrostis curvula, Cynodon sp and Distichlis spicata) growing in seminatural grassland of central Argentina were selected to study their capability to incorporate Cs + (and K + ) using electrophysiological techniques. Although the 137 Cs soil inventory ranged between 328-730 Bq m -2 in this region, no 137 Cs activity was detected in these plants. However, all the species, submitted previously to K + starvation, showed the uptake of both Cs + and K + when micromolar concentrations of these cations were present in the medium. The uptake showed saturation kinetics for both cations that could be fitted to the Michelis-Menten model. K M values were smaller for K + than for Cs + , indicating a higher affinity for the first cation. The presence of increasing K + concentrations in the assay medium inhibited Cs + uptake in Cynodon sp., as expected if both cations are transported by the same transport systems. This effect is due to the competition of both ions for the union sites of the high affinity potassium transporters. In field situation, where soil concentration of Cs + is smaller than K + concentration, is then expectable that caesium activity in plants is not detectable. Nevertheless, the studied plants would have the capacity to incorporate caesium if its availability in soil solution increases. In addition, studies of Cs/K interaction can help us to understand the variability in transfer factors

  6. Journal of Chemical Sciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    ... behaves as an effective catalyst towards oxidation of 3,5-ditertiarybutyl catechol (3,5-DTBC) in acetonitrile to its corresponding quinone derivative in air. The reaction follows first-order reaction kinetics with rate constant 4.28 × 10−5 min-1. The reaction follows Michaelis-Menten enzymatic kinetics with a turnover number of ...

  7. Journal of Chemical Sciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants.

  8. Picolinic acid promoted oxidative decarboxylation of ...

    African Journals Online (AJOL)

    The kinetics and mechanism of picolinic acid promoted reaction of phenylsulfinylacetic acid (PSAA) with Cr(VI) was carried out in aqueous acetonitrile medium under pseudo first order conditions. The reaction follows Michaelis-Menten type of kinetics with respect to PSAA. The catalytic activity by picolinic acid can be ...

  9. Kinetics of phosphate uptake, growth, and accumulation of cyclic diphosphoglycerate in a phosphate-limited continuous culture of Methanobacterium thermoautotrophicum.

    Science.gov (United States)

    Krueger, R D; Harper, S H; Campbell, J W; Fahrney, D E

    1986-07-01

    The archaebacterium Methanobacterium thermoautotrophicum was grown in continuous culture at 65 degrees C in a phosphate-limited medium at specific growth rates from 0.06 to 0.28 h-1 (maximum growth rate [mu max] = 0.36 h-1). Cyclic-2,3-diphosphoglycerate (cyclic DPG) levels ranged from 2 to 20 mM in Pi-limited cells, compared with about 30 mM in batch-grown cells. The Monod constant for Pi-limited growth was 5 nM. Pi uptake rates were determined by following the disappearance of 32Pi from the medium. Interrupting the H2 supply stopped the uptake of Pi and the release of organic phosphates. Little or no efflux of Pi occurred in the presence or absence of H2. Pi uptake of cells adapted to nanomolar Pi concentrations could be accounted for by the operation of one uptake system with an apparent Km of about 25 nM and a Vmax of 58 nmol of Pi per min per g (dry weight). Uptake curves at 30 microM Pi or above were biphasic due to a sevenfold decrease in Vmax after an initial phase of rapid movement of Pi into the cell. Under these conditions the growth rate slowed to zero and the cyclic DPG pool expanded before growth resumed. Thus, three properties of M. thermoautotrophicum make it well adapted to live in a low-P environment: the presence of a low-Km, high-Vmax uptake system for Pi; the ability to accumulate cyclic DPG rapidly; and a growth strategy in which accumulation of Pi and cyclic DPG takes precedence over a shift-up in growth rate when excess Pi becomes available.

  10. Kinetics of phosphate uptake, growth, and accumulation of cyclic diphosphoglycerate in a phosphate-limited continuous culture of Methanobacterium thermoautotrophicum.

    Science.gov (United States)

    Krueger, R D; Harper, S H; Campbell, J W; Fahrney, D E

    1986-01-01

    The archaebacterium Methanobacterium thermoautotrophicum was grown in continuous culture at 65 degrees C in a phosphate-limited medium at specific growth rates from 0.06 to 0.28 h-1 (maximum growth rate [mu max] = 0.36 h-1). Cyclic-2,3-diphosphoglycerate (cyclic DPG) levels ranged from 2 to 20 mM in Pi-limited cells, compared with about 30 mM in batch-grown cells. The Monod constant for Pi-limited growth was 5 nM. Pi uptake rates were determined by following the disappearance of 32Pi from the medium. Interrupting the H2 supply stopped the uptake of Pi and the release of organic phosphates. Little or no efflux of Pi occurred in the presence or absence of H2. Pi uptake of cells adapted to nanomolar Pi concentrations could be accounted for by the operation of one uptake system with an apparent Km of about 25 nM and a Vmax of 58 nmol of Pi per min per g (dry weight). Uptake curves at 30 microM Pi or above were biphasic due to a sevenfold decrease in Vmax after an initial phase of rapid movement of Pi into the cell. Under these conditions the growth rate slowed to zero and the cyclic DPG pool expanded before growth resumed. Thus, three properties of M. thermoautotrophicum make it well adapted to live in a low-P environment: the presence of a low-Km, high-Vmax uptake system for Pi; the ability to accumulate cyclic DPG rapidly; and a growth strategy in which accumulation of Pi and cyclic DPG takes precedence over a shift-up in growth rate when excess Pi becomes available. PMID:3722128

  11. Technical note: Influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies

    Directory of Open Access Journals (Sweden)

    G. Li

    2018-02-01

    Full Text Available Coated-wall flow tube reactors are frequently used to investigate gas uptake and heterogeneous or multiphase reaction kinetics under laminar flow conditions. Coating surface roughness may potentially distort the laminar flow pattern, induce turbulence and introduce uncertainties in the calculated uptake coefficient based on molecular diffusion assumptions (e.g., Brown/Cooney–Kim–Davis (CKD/Knopf–Pöschl–Shiraiwa (KPS methods, which has not been fully resolved in earlier studies. Here, we investigate the influence of surface roughness and local turbulence on coated-wall flow tube experiments for gas uptake and kinetic studies. According to laminar boundary theory and considering the specific flow conditions in a coated-wall flow tube, we derive and propose a critical height δc to evaluate turbulence effects in the design and analysis of coated-wall flow tube experiments. If a geometric coating thickness δg is larger than δc, the roughness elements of the coating may cause local turbulence and result in overestimation of the real uptake coefficient (γ. We further develop modified CKD/KPS methods (i.e., CKD-LT/KPS-LT to account for roughness-induced local turbulence effects. By combination of the original methods and their modified versions, the maximum error range of γCKD (derived with the CKD method or γKPS (derived with the KPS method can be quantified and finally γ can be constrained. When turbulence is generated, γCKD or γKPS can bear large difference compared to γ. Their difference becomes smaller for gas reactants with lower uptake (i.e., smaller γ and/or for a smaller ratio of the geometric coating thickness to the flow tube radius (δg ∕ R0. On the other hand, the critical height δc can also be adjusted by optimizing flow tube configurations and operating conditions (i.e., tube diameter, length, and flow velocity, to ensure not only unaffected laminar flow patterns but also other specific requirements for an

  12. Uptake, translocation and biotransformation kinetics of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.).

    Science.gov (United States)

    Xu, Xuehui; Wen, Bei; Huang, Honglin; Wang, Sen; Han, Ruixia; Zhang, Shuzhen

    2016-01-01

    This study presents a detailed kinetic investigation on the uptake, acropetal translocation and transformation of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.) by hydroponic exposure. Root uptake followed the order: BDE-47 > 6-MeO-BDE-47 > 6-OH-BDE-47, while 6-OH-BDE-47 was the most prone to acropetal translocation. Debromination rates of BDE-47 were 1.31 and 1.46 times greater than the hydroxylation and methoxylation rates, respectively. Transformation from BDE-47 to lower brominated OH/MeO-PBDEs occurred mainly through debromination first followed by hydroxylation or methoxylation. There was no transformation from 6-OH-BDE-47 or 6-MeO-BDE-47 to PBDEs. Methylation rate of 6-OH-BDE-47 was twice as high as that of 6-MeO-BDE-47 hydroxylation, indicating methylation of 6-OH-BDE-47 was easier and more rapid than hydroxylation of 6-MeO-BDE-47. Debromination and isomerization were potential metabolic pathways for 6-OH-BDE-47 and 6-MeO-BDE-47 in maize. This study provides important information for better understanding the mechanism on plant uptake and transformation of PBDEs. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Kinetics of phosphorus and potassium release from rock phosphate and waste mica enriched compost and their effect on yield and nutrient uptake by wheat (Triticum aestivum).

    Science.gov (United States)

    Nishanth, D; Biswas, D R

    2008-06-01

    An attempt was made to study the efficient use of rice straw and indigenous source of phosphorus and potassium in crop production through composting technology. Various enriched composts were prepared using rice straw, rock phosphate (RP), waste mica and bioinoculant (Aspergillus awamori) and kinetics of release of phosphorus and potassium from enriched composts and their effect on yield and nutrient uptake by wheat (Triticum aestivum) were carried out. Results showed sharp increases in release in water-soluble P and K from all the composts at 8th to 12th day of leaching, thereafter, it decreased gradually. Maximum release of water-soluble P and K were obtained in ordinary compost than enriched composts during the initial stages of leaching, but their differences narrowed down at latter stages. Data in pot experiments revealed that enriched composts performed poorly than diammonium phosphate during initial stages of crop growth, but they out yielded at the latter stages, particularly at maturity stage, as evident from their higher yield, uptake, nutrient recoveries and fertility status of P and K in soils. Moreover, enriched composts prepared with RP and waste mica along with A. awamori resulted in significantly higher biomass yield, uptake and recoveries of P and K as well as available P and K in soils than composts prepared without inoculant. Results indicated that enriched compost could be an alternate technology for the efficient management of rice straw, low-grade RP and waste mica in crop production, which could help to reduce the reliance on costly chemical fertilizers.

  14. Competition between organics and bromide at the aqueous solution-air interface as seen from ozone uptake kinetics and X-ray photoelectron spectroscopy.

    Science.gov (United States)

    Lee, Ming-Tao; Brown, Matthew A; Kato, Shunsuke; Kleibert, Armin; Türler, Andreas; Ammann, Markus

    2015-05-14

    A more detailed understanding of the heterogeneous chemistry of halogenated species in the marine boundary layer is required. Here, we studied the reaction of ozone (O3) with NaBr solutions in the presence and absence of citric acid (C6H8O7) under ambient conditions. Citric acid is used as a proxy for oxidized organic material present at the ocean surface or in sea spray aerosol. On neat NaBr solutions, the observed kinetics is consistent with bulk reaction-limited uptake, and a second-order rate constant for the reaction of O3 + Br(-) is 57 ± 10 M(-1) s(-1). On mixed NaBr-citric acid aqueous solutions, the uptake kinetics was faster than that predicted by bulk reaction-limited uptake and also faster than expected based on an acid-catalyzed mechanism. X-ray photoelectron spectroscopy (XPS) on a liquid microjet of the same solutions at 1.0 × 10(-3)-1.0 × 10(-4) mbar was used to obtain quantitative insight into the interfacial composition relative to that of the bulk solutions. It revealed that the bromide anion becomes depleted by 30 ± 10% while the sodium cation gets enhanced by 40 ± 20% at the aqueous solution-air interface of a 0.12 M NaBr solution mixed with 2.5 M citric acid in the bulk, attributed to the role of citric acid as a weak surfactant. Therefore, the enhanced reactivity of bromide solutions observed in the presence of citric acid is not necessarily attributable to a surface reaction but could also result from an increased solubility of ozone at higher citric acid concentrations. Whether the acid-catalyzed chemistry may have a larger effect on the surface than in the bulk to offset the effect of bromide depletion also remains open.

  15. Reproducibility of O-(2-{sup 18}F-fluoroethyl)-L-tyrosine uptake kinetics in brain tumors and influence of corticoid therapy: an experimental study in rat gliomas

    Energy Technology Data Exchange (ETDEWEB)

    Stegmayr, Carina; Schoeneck, Michael; Oliveira, Dennis; Willuweit, Antje [Institute of Neuroscience and Medicine, Research Center Juelich, Juelich (Germany); Filss, Christian; Coenen, Heinz H.; Langen, Karl-Josef [Institute of Neuroscience and Medicine, Research Center Juelich, Juelich (Germany); University of Aachen, Department of Nuclear Medicine and Neurology, Aachen (Germany); Galldiks, Norbert [Institute of Neuroscience and Medicine, Research Center Juelich, Juelich (Germany); University of Cologne, Department of Neurology, Cologne (Germany); Shah, N. Jon [Institute of Neuroscience and Medicine, Research Center Juelich, Juelich (Germany); University of Aachen, Department of Nuclear Medicine and Neurology, Aachen (Germany); Juelich-Aachen Research Alliance (JARA) - Section JARA-Brain, Juelich (Germany)

    2016-06-15

    Positron emission tomography (PET) using O-(2-{sup 18}F-fluoroethyl)-L-tyrosine ({sup 18}F-FET) is a well-established method for the diagnostics of brain tumors. This study investigates reproducibility of {sup 18}F-FET uptake kinetics in rat gliomas and the influence of the frequently used dexamethasone (Dex) therapy. F98 glioma or 9L gliosarcoma cells were implanted into the striatum of 31 Fischer rats. After 10-11 days of tumor growth, the animals underwent dynamic PET after injection of {sup 18}F-FET (baseline). Thereafter, animals were divided into a control group and a group receiving Dex injections, and all animals were reinvestigated 2 days later. Tumor-to-brain ratios (TBR) of {sup 18}F-FET uptake (18-61 min p.i.) and the slope of the time-activity-curves (TAC) (18-61 min p.i.) were evaluated using a Volume-of-Interest (VOI) analysis. Data were analyzed by two-way repeated measures ANOVA and reproducibility by the intraclass correlation coefficient (ICC). The slope of the tumor TACs showed high reproducibility with an ICC of 0.93. A systematic increase of the TBR in the repeated scans was noted (3.7 ± 2.8 %; p < 0.01), and appeared to be related to tumor growth as indicated by a significant correlation of TBR and tumor volume (r = 0.77; p < 0.0001). After correction for tumor growth TBR showed high longitudinal stability with an ICC of 0.84. Dex treatment induced a significant decrease of the TBR (-8.2 ± 6.1 %; p < 0.03), but did not influence the slope of the tumor TAC. TBR of {sup 18}F-FET uptake and tracer kinetics in brain tumors showed high longitudinal stability. Dex therapy may induce a minor decrease of the TBR; this needs further investigation. (orig.)

  16. Modeling the oxygen uptake kinetics during exercise testing of patients with chronic obstructive pulmonary diseases using nonlinear mixed models

    DEFF Research Database (Denmark)

    Baty, Florent; Ritz, Christian; van Gestel, Arnoldus

    2016-01-01

    describe functionality of the R package medrc that extends the framework of the commonly used packages drc and nlme and allows fitting nonlinear mixed effects models for automated nonlinear regression modeling. The methodology was applied to a data set including 6MWT [Formula: see text]O2 kinetics from 61...... patients with chronic obstructive pulmonary disease (disease severity stage II to IV). The mixed effects approach was compared to a traditional curve-by-curve approach. RESULTS: A six-parameter nonlinear regression model was jointly fitted to the set of [Formula: see text]O2 kinetics. Significant...

  17. Kinetic modelling of in vitro data of PI3K, mTOR1, PTEN enzymes and on-target inhibitors Rapamycin, BEZ235, and LY294002.

    Science.gov (United States)

    Goltsov, Alexey; Tashkandi, Ghassan; Langdon, Simon P; Harrison, David J; Bown, James L

    2017-01-15

    The phosphatidylinositide 3-kinases (PI3K) and mammalian target of rapamycin-1 (mTOR1) are two key targets for anti-cancer therapy. Predicting the response of the PI3K/AKT/mTOR1 signalling pathway to targeted therapy is made difficult because of network complexities. Systems biology models can help explore those complexities but the value of such models is dependent on accurate parameterisation. Motivated by a need to increase accuracy in kinetic parameter estimation, and therefore the predictive power of the model, we present a framework to integrate kinetic data from enzyme assays into a unified enzyme kinetic model. We present exemplar kinetic models of PI3K and mTOR1, calibrated on in vitro enzyme data and founded on Michaelis-Menten (MM) approximation. We describe the effects of an allosteric mTOR1 inhibitor (Rapamycin) and ATP-competitive inhibitors (BEZ235 and LY294002) that show dual inhibition of mTOR1 and PI3K. We also model the kinetics of phosphatase and tensin homolog (PTEN), which modulates sensitivity of the PI3K/AKT/mTOR1 pathway to these drugs. Model validation with independent data sets allows investigation of enzyme function and drug dose dependencies in a wide range of experimental conditions. Modelling of the mTOR1 kinetics showed that Rapamycin has an IC 50 independent of ATP concentration and that it is a selective inhibitor of mTOR1 substrates S6K1 and 4EBP1: it retains 40% of mTOR1 activity relative to 4EBP1 phosphorylation and inhibits completely S6K1 activity. For the dual ATP-competitive inhibitors of mTOR1 and PI3K, LY294002 and BEZ235, we derived the dependence of the IC 50 on ATP concentration that allows prediction of the IC 50 at different ATP concentrations in enzyme and cellular assays. Comparison of drug effectiveness in enzyme and cellular assays showed that some features of these drugs arise from signalling modulation beyond the on-target action and MM approximation and require a systems-level consideration of the whole PI3K

  18. Uptake, translocation and biotransformation kinetics of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.)

    International Nuclear Information System (INIS)

    Xu, Xuehui; Wen, Bei; Huang, Honglin; Wang, Sen; Han, Ruixia; Zhang, Shuzhen

    2016-01-01

    This study presents a detailed kinetic investigation on the uptake, acropetal translocation and transformation of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 in maize (Zea mays L.) by hydroponic exposure. Root uptake followed the order: BDE-47 > 6-MeO-BDE-47 > 6-OH-BDE-47, while 6-OH-BDE-47 was the most prone to acropetal translocation. Debromination rates of BDE-47 were 1.31 and 1.46 times greater than the hydroxylation and methoxylation rates, respectively. Transformation from BDE-47 to lower brominated OH/MeO-PBDEs occurred mainly through debromination first followed by hydroxylation or methoxylation. There was no transformation from 6-OH-BDE-47 or 6-MeO-BDE-47 to PBDEs. Methylation rate of 6-OH-BDE-47 was twice as high as that of 6-MeO-BDE-47 hydroxylation, indicating methylation of 6-OH-BDE-47 was easier and more rapid than hydroxylation of 6-MeO-BDE-47. Debromination and isomerization were potential metabolic pathways for 6-OH-BDE-47 and 6-MeO-BDE-47 in maize. This study provides important information for better understanding the mechanism on plant uptake and transformation of PBDEs. - Highlights: • Uptake and translocation of BDE-47 and 6-OH/MeO-BDE-47 were analog-specific. • Debromination was the fast and dominant metabolic reaction of BDE-47 in maize. • Metabolic pathways of BDE-47, 6-OH/MeO-BDE-47 in maize were discussed. • Metabolic processes should be considered in exploring phytoremediation strategy. - This article provides direct in vivo evidences of bioaccumulation and biotransformation of PBDEs, OH-PBDEs and MeO-PBDEs in plants.

  19. A short period of high-intensity interval training improves skeletal muscle mitochondrial function and pulmonary oxygen uptake kinetics

    DEFF Research Database (Denmark)

    Christensen, Peter Møller; Jacobs, Robert A; Bonne, Thomas Christian

    2016-01-01

    The aim of the present study was to examine whether improvements in pulmonary V̇O2 kinetics following a short period of high-intensity training (HIT) would be associated with improved skeletal muscle mitochondrial function. Ten untrained male volunteers (age: 26 ± 2; mean ± SD) performed six HIT...

  20. 99Tcm-N(NOEt2 Uptake Kinetics Difference among KMB17 Human Embryonic Lung Diploid Fibroblast and Different Human Lung Cancer Cells

    Directory of Open Access Journals (Sweden)

    Wei JIA

    2010-04-01

    Full Text Available Background and objective PET/CT imaging is expensive, so searching the tumor imaging agent for SPECT/CT is necessary. 99Tcm-N(NOEt2 [bis (N-ethoxy-N-ethyl dithiocarbamato nitrido99Tcm (V] can be uptaken by lung cancer cells and other cells alike. The aim of this study is to evaluate the distinctive value in lung tumor with 99Tcm-N(NOEt2, the difference in its uptake kinetics in human embryonic lung diploid fibroblasts KMB17 and several kinds of lung cancer cells lines. Methods Firstly, six different cell culture medium which contained YTMLC Gejiu human lung squamous carcinoma cell, SPC-A1 human lung adenocarcinoma cell, AGZY low metastatic human lung adenocarcinoma, 973 high metastatic human lung adenocarcinoma cell, GLC-82 Gejiu human lung adenocarcinoma cell, and KMB17 human embryonic lung diploid fibroblast, respectively with equal cell density of 1×106/mL and the same volume were prepared; secondly, the same radioactive dose of 99Tcm-N(NOEt2 was added into each sample and then 300 μL mixed sample was taken out respectively and cultured in 37 oC culture box; Finally, 5 min, 15 min, 30 min, 45 min, 60 min, 75 min, 90 min after cultivation, centrifuged each cultured sample and determined the intracellular radiocounts of each sample, calculated each cell sample’s uptake rate of 99Tcm-N(NOEt2 at different time. Results Statistical difference was found among six cell samples, and the uptake rate sequence from high to low is 973 and SPC-A1>YTMLC>GLC-82>AGZY>KMB17 respectively; furthermore, 30 min-45 min after culture, the uptake rate reached stability, and the 45 min uptake rate of each sample was higher than its 96.7% uptake peak. Conclusion Based on the results above mentioned, it is supposed that there are discriminative clinical value when using 99Tcm-N(NOEt2 as a tumor targeting imaging agent, and 30 min or so after injection may be the best imaging time in the early imaging stage.

  1. Genetic characterization, nickel tolerance, biosorption, kinetics, and uptake mechanism of a bacterium isolated from electroplating industrial effluent.

    Science.gov (United States)

    Nagarajan, N; Gunasekaran, P; Rajendran, P

    2015-04-01

    Electroplating industries in Madurai city produce approximately 49,000 L of wastewater and 1200 L of sludge every day revealing 687-5569 ppm of nickel (Ni) with other contaminants. Seventeen Ni-tolerant bacterial strains were isolated from nutrient-enriched effluents. Among them one hyper Ni accumulating strain was scored and identified as Bacillus cereus VP17 on the basis of morphology, biochemical tests, 16S rDNA gene sequencing, and phylogenetic analysis. Equilibrium data of Ni(II) ions using the bacterium as sorbent at isothermal conditions (37 °C) and pH 6 were best adjusted by Langmuir (R(2) = 0.6268) and Freundlich models (R(2) = 0.9505). Experimental validation reveals Ni sorption takes place on a heterogeneous surface of the biosorbent, and predicted metal sorption capacity is 434 ppm. The pseudo-second-order kinetic model fitted the biosorption kinetic data better than the pseudo-first-order kinetic model (R(2) = 0.9963 and 0.3625). Scanning electron microscopy, energy dispersive X-ray, and Fourier transform infrared spectroscopy studies of the bacterial strain with and without Ni(II) ion reveals the biosorption mechanism. The results conclude possibilities of using B. cereus VP17 for Ni bioremediation.

  2. Uptake and release kinetics of 134Cs by goldfish (Carassius auratus) and 137Cs by zebra fish (Brachydanio rerio) in controlled aquatic environment

    International Nuclear Information System (INIS)

    Srivastava, A.; Reddy, S.J.; Kelber, O.; Urich, K.; Denschlag, H.O.

    1994-01-01

    The uptake and release kinetics of 134 Cs by Goldfish (Carassius auratus) and 137 Cs by Zebra Fish (Brachydanio rerio) from aquatic media of different ionic compositions and temperature was studied in controlled laboratory conditions. The accumulation of radiocesium in the case of Brachydanio rerio is observed to be strongly dependent on the potassium ion concentration of the aquatic medium, but in the case of Carassius auratus this dependence is quite weak. The biological half-lives of the cesium isotopes incorporated into the fish investigated in the present work vary from 19 to 80 days and are influenced by the temperature and the ionic composition of the aquatic medium. (author) 19 refs.; 1 fig.; 3 tabs

  3. Kinetics of alcoholic fermentation during the culturing of bakers' yeast

    Energy Technology Data Exchange (ETDEWEB)

    Franz, B

    1961-01-01

    A synthesis was made of the effects of various factors on the rate of fermentation by Saccharomyces cerevisiae. The rate obeyed the Michaelis-Menten equation, was independent of the concentration of yeast, was maximal at 20/sup 0/ (0.61 ml ethanol/g dry yeast/h), was not significantly affected between pH 6.5 and 3.0 but declined at 3.0, was inhibited by ethanol at a rate proportional to the concentration squared (at ethanol = 12 volume %, the fermentation rate was practically zero), and was enhanced by the addition of phosphorus when a P-poor yeast was employed.

  4. Iodine capsules in thyroid therapy: An individually controlled study of I-131 uptake kinetics as compared to liquid administration

    International Nuclear Information System (INIS)

    von Schulthess, G.K.; Seelentag, W.W.; Pfeiffer, G.; Blauenstein, P.; Bekier, A.

    1984-01-01

    The aim of this study was to determine the additional radiation dose sustained by parts of the patients gastric mucosa when given I-131 therapy in capsular rather than liquid form, and thus to establish the safety of this procedure. 16 patients with benign thyroid disease were studied by measuring serum radioactivity at 0, 5, 10, 20, 40, and 80 min. after administration of the capsule (120-200 MBq I131). These serum uptake values were compared to the uptake after administration of a liquid diagnostic dose of I-131 (2 MBq). From the resulting uptake curves the delay due to capsular dissolution was determined. The average dissolution time was found to be 12 min. with a large standard deviation of 7 min. Also, a theoretical curve was computed to indicate the dose rate as a function of the distance from the surface of the capsule. Based on this information the maximum dose to the gastric mucosa is of the order of 250 cGy for a therapeutic activity of 185 MBq, which is the maximum dose which may be given as single application to outpatients in Switzerland. By having the patient swallow some liquid during the first ten minutes, the capsule can be made to move around, and hence, the local radiation dose can be reduced substantially. The authors conclude, that I-131 in capsular form is a safe galenic form for therapeutic use in patients with thyroid disease. When large doses are given, administration of the dose in several capsules may be advisable

  5. Kinetics of phosphate uptake, growth, and accumulation of cyclic diphosphoglycerate in a phosphate-limited continuous culture of Methanobacterium thermoautotrophicum.

    OpenAIRE

    Krueger, R D; Harper, S H; Campbell, J W; Fahrney, D E

    1986-01-01

    The archaebacterium Methanobacterium thermoautotrophicum was grown in continuous culture at 65 degrees C in a phosphate-limited medium at specific growth rates from 0.06 to 0.28 h-1 (maximum growth rate [mu max] = 0.36 h-1). Cyclic-2,3-diphosphoglycerate (cyclic DPG) levels ranged from 2 to 20 mM in Pi-limited cells, compared with about 30 mM in batch-grown cells. The Monod constant for Pi-limited growth was 5 nM. Pi uptake rates were determined by following the disappearance of 32Pi from the...

  6. Signaling Cascades: Consequences of Varying Substrate and Phosphatase Levels

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Knudsen, Michael; Wiuf, Carsten Henrik

    2012-01-01

    We study signaling cascades with an arbitrary number of layers of one-site phosphorylation cycles. Such cascades are abundant in nature and integrated parts of many pathways. Based on the Michaelis-Menten model of enzyme kinetics and the law of mass-action, we derive explicit analytic expressions...

  7. MODELING OF MIXED CHEMOSTAT CULTURES OF AN AEROBIC BACTERIUM, COMAMONAS-TESTOSTERONI, AND AN ANAEROBIC BACTERIUM, VEILLONELLA-ALCALESCENS - COMPARISON WITH EXPERIMENTAL-DATA

    NARCIS (Netherlands)

    GERRITSE, J; SCHUT, F; GOTTSCHAL, JC

    A mathematical model of mixed chemostat cultures of the obligately aerobic bacterium Comamonas testosteroni and the anaerobic bacterium Veillonella alcalescens grown under dual limitation Of L-lactate and oxygen was constructed. The model was based on Michaelis-Menten-type kinetics for the

  8. Metabolic stereoselectivity of cytochrome P450 3A4 towards deoxypodophyllotoxin : In silico predictions and experimental validation

    NARCIS (Netherlands)

    Julsing, Mattijs K.; Vasilev, Nikolay P.; Schneidman-Duhovny, Dina; Muntendarn, Remco; Woerdenbag, Herman J.; Quax, Wim J.; Wolfson, Haim J.; Ionkova, Iliana; Kayser, Oliver

    Deoxypodophyllotoxin is stereoselectively converted into epipodophyllotoxin by recombinant human cytochrome P450 3A4 (CY-P3A4). Further kinetic analysis revealed that the Michaelis-Menten K(m) and V(max) for hydroxylation of deoxypodophyllotoxin by CYP3A4 at C7 position were 1.93 mu M and 1.48

  9. Wang and Li Afr J Tradit Complement Altern Med. (2016) 13(1):99 ...

    African Journals Online (AJOL)

    PROF ADEWUNMI

    It possesses antiseptic, anti-inflammatory, analgesic, anti-cancer and antioxidant ... All experiments on animals were conducted in accordance with and after approval by the ... With the content of gallic acid control as horizontal coordinate and the ... The kinetic constants were calculated based on Michaelis-Menten equation ...

  10. Journal of Chemical Sciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    The oxidation of eleven amino acids by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid results in the formation of the corresponding carbonyl compounds and ammonia. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with some of the amino acids while others ...

  11. Purification and characterization of a chlorite dismutase from Pseudomonas chloritidismutans

    NARCIS (Netherlands)

    Mehboob, F.; Wolterink, A.F.W.M.; Vermeulen, A.J.; Jiang, B.; Hagedoorn, P.L.; Stams, A.J.M.; Kengen, S.W.M.

    2009-01-01

    The chlorite dismutase (Cld) of Pseudomonas chloritidismutans was purified from the periplasmic fraction in one step by hydroxyapatite chromatography. The enzyme has a molecular mass of 110 kDa and consists of four 31-kDa subunits. Enzyme catalysis followed Michaelis-Menten kinetics, with Vmax and

  12. Cyclodextrin Aldehydes are Oxidase Mimics

    DEFF Research Database (Denmark)

    Fenger, Thomas Hauch; Bjerre, Jeannette; Bols, Mikael

    2009-01-01

    Cyclodextrins containing 6-aldehyde groups were found to catalyse oxidation of aminophenols in the presence of hydrogen peroxide. The catalysis followed Michaelis-Menten kinetics and is related to the catalysis previously observed with cyclodextrin ketones. A range of different cyclodextrin aldeh...

  13. International Meeting on Cholinesterases (5th) Held in Madras, India on 24-28 September, 1994.

    Science.gov (United States)

    1994-09-01

    found that hydrolysis of thioesters deviated from simple Michaelis-Menten model. Kinetics was triphasic , displaying complexities of both BuChE and ACHE...of recombinant human acetylcholinesterase (rHuAChE) produced by human embryonic kidney cell line (293) in a fixed-bed reactor (1) was investigated at

  14. Kinetic box models for the uptake of radionuclides and heavy metals by suspended particulate matter: equivalence between models and its implications

    International Nuclear Information System (INIS)

    Barros, H.; Abril, J.M.

    2008-01-01

    In recent years an increasing experimental effort has been paid to the study of the sorption process of radionuclides and heavy metals by particulate matter in aquatic environments. This has led to the development of different kinetic box models. Most of them are variations of two basic approaches: one containing several (up to three) parallel reactions while the other involves consecutive reactions. All the reactions are reversible (irreversibility is contained as a particular case) with concentration independent coefficients. The present work provides analytical solutions and demonstrates that both approaches are mathematically equivalent. That is, both models produce the same analytical solution for the uptake curve (time course of the concentrations in the dissolved phase), which is illustrated using literature data. This result unifies the description of the observed behaviour, but it brings up the question of the physical meaning of the involved coefficients. Finally, the mathematical relationship developed here serves to discuss some limitations found in recent attempts in literature devoted to distinguish the actual uptake mechanism

  15. Differentiation of Glioblastomas from Metastatic Brain Tumors by Tryptophan Uptake and Kinetic Analysis: A Positron Emission Tomographic Study with Magnetic Resonance Imaging Comparison

    Directory of Open Access Journals (Sweden)

    David O. Kamson

    2013-07-01

    Full Text Available Differentiating high-grade gliomas from solitary brain metastases is often difficult by conventional magnetic resonance imaging (MRI; molecular imaging may facilitate such discrimination. We tested the accuracy of α[11C]methyl-L-tryptophan (AMT–positron emission tomography (PET to differentiate newly diagnosed glioblastomas from brain metastases. AMT-PET was performed in 36 adults with suspected brain malignancy. Tumoral AMT accumulation was measured by standardized uptake values (SUVs. Tracer kinetic analysis was also performed to separate tumoral net tryptophan transport (by AMT volume of distribution [VD] from unidirectional uptake rates using dynamic PET and blood input function. Differentiating the accuracy of these PET variables was evaluated and compared to conventional MRI. For glioblastoma/metastasis differentiation, tumoral AMT SUV showed the highest accuracy (74% and the tumor/cortex VD ratio had the highest positive predictive value (82%. The combined accuracy of MRI (size of contrast-enhancing lesion and AMT-PET reached up to 93%. For ring-enhancing lesions, tumor/cortex SUV ratios were higher in glioblastomas than in metastatic tumors and could differentiate these two tumor types with > 90% accuracy. These results demonstrate that evaluation of tryptophan accumulation by PET can enhance pretreatment differentiation of glioblastomas and metastatic brain tumors. This approach may be particularly useful in patients with a newly diagnosed solitary ring-enhancing mass.

  16. Photocurrents in retinal rods of pigeons (Columba livia): kinetics and spectral sensitivity.

    Science.gov (United States)

    Palacios, A G; Goldsmith, T H

    1993-01-01

    1. Membrane photocurrents were recorded from outer segments of isolated retinal rods of pigeons (Columba livia), the first such measurements on the photoreceptors of a bird. The amplitude of the response to 20 ms flashes of narrow wavelength bands of light increases linearly with intensity at low photon fluxes and saturates at higher intensities. The maximum (saturating) photocurrent observed in forty-nine rod cells was 50 pA. Larger responses with less variability in the intensity for half-maximal responses were observed when the physiological saline contained 20 mM bicarbonate (in addition to Hepes buffer). 2. The dependence of peak amplitude on intensity is well fitted by an exponential function; it is usually less well fitted by the Michaelis-Menten (Naka-Rushton) equation. 3. In the presence of bicarbonate, the average sensitivity of pigeon rods to dim flashes was 0.56 pA photon-1 microns -2. The effective collecting area per photon was 1.8 microns 2. About 83 +/- 26 (mean +/- S.D.) photoisomerizations were required for a half-saturating response. 4. The response kinetics of rods to dim flashes can be reasonably well described by a series of four to five either Poisson or independent filters. The time to peak, measured from the mid-point of a 20 ms flash, was 319 +/- 83 ms (mean +/- S.D.). The integration time of the response was 851 +/- 86 ms (mean +/- S.D.) with bicarbonate present and 572 +/- 126 ms in the absence of bicarbonate. The responses of pigeon rods appear to be slower than those of mammals at the same temperature. The fraction of current suppressed by a single photoisomerization is smaller in pigeon than in mammalian rods by a factor of at least two. 5. The spectral sensitivity function was measured between 680 and 330 nm. The maximum at about 505 nm (range 497-508 nm) corresponds to the alpha-band of a vertebrate rhodopsin and agrees with previous behavioural measurements of scotopic sensitivity of pigeons as well as the absorption spectrum of

  17. Kinetic study of phytotoxicity induced by foliar lead uptake for vegetables exposed to fine particles and implications for sustainable urban agriculture.

    Science.gov (United States)

    Xiong, TianTian; Austruy, Annabelle; Pierart, Antoine; Shahid, Muhammad; Schreck, Eva; Mombo, Stéphane; Dumat, Camille

    2016-08-01

    At the global scale, foliar metal transfer occurs for consumed vegetables cultivated in numerous urban or industrial areas with a polluted atmosphere. However, the kinetics of metal uptake, translocation and involved phytotoxicity was never jointly studied with vegetables exposed to micronic and sub-micronic particles (PM). Different leafy vegetables (lettuces and cabbages) cultivated in RHIZOtest® devices were, therefore, exposed in a greenhouse for 5, 10 and 15days to various PbO PM doses. The kinetics of transfer and phytotoxicity was assessed in relation to lead concentration and exposure duration. A significant Pb accumulation in leaves (up to 7392mg/kg dry weight (DW) in lettuce) with translocation to roots was observed. Lead foliar exposure resulted in significant phytotoxicity, lipid composition change, a decrease of plant shoot growth (up to 68.2% in lettuce) and net photosynthesis (up to 58% in lettuce). The phytotoxicity results indicated plant adaptation to Pb and a higher sensitivity of lettuce in comparison with cabbage. Air quality needs, therefore, to be considered for the health and quality of vegetables grown in polluted areas, such as certain megacities (in China, Pakistan, Europe, etc.) and furthermore, to assess the health risks associated with their consumption. Copyright © 2016. Published by Elsevier B.V.

  18. The uptake of NO3-, NO2-, and NH4+ by intact wheat (Triticum aestivum) seedlings. I. Induction and kinetics of transport systems

    Science.gov (United States)

    Goyal, S. S.; Huffaker, R. C.

    1986-01-01

    The inducibility and kinetics of the NO3-, NO2-, and NH4+ transporters in roots of wheat seedlings (Triticum aestivum cv Yercora Rojo) were characterized using precise methods approaching constant analysis of the substrate solutions. A microcomputer-controlled automated high performance liquid chromatography system was used to determine the depletion of each N species (initially at 1 millimolar) from complete nutrient solutions. Uptake rate analyses were performed using computerized curve-fitting techniques. More precise estimates were obtained for the time required for the extent of the induction of each transporter. Up to 10 and 6 hours, respectively, were required to achieve apparent full induction of the NO3- and NO2- transporters. Evidence for substrate inducibility of the NH4+ transporters requiring 5 hours is presented. The transport of NO3- was mediated by a dual system (or dual phasic), whereas only single systems were found for transport of NO2- and NH4+. The Km values for NO3-, NO2-, and NH4+ were, respectively, 0.027, 0.054, and 0.05 millimolar. The Km for mechanism II of NO3- transport could not be defined in this study as it exhibited only apparent first order kinetics up to 1 millimolar.

  19. Influence of priming exercise on pulmonary O2 uptake kinetics during transitions to high-intensity exercise from an elevated baseline.

    Science.gov (United States)

    DiMenna, Fred J; Wilkerson, Daryl P; Burnley, Mark; Jones, Andrew M

    2008-08-01

    It has been suggested that the slower O2 uptake (VO2) kinetics observed when exercise is initiated from an elevated baseline metabolic rate are linked to an impairment of muscle O2 delivery. We hypothesized that "priming" exercise would significantly reduce the phase II time constant (tau) during subsequent severe-intensity cycle exercise initiated from an elevated baseline metabolic rate. Seven healthy men completed exercise transitions to 70% of the difference between gas exchange threshold (GET) and peak VO2 from a moderate-intensity baseline (90% GET) on three occasions in each of the "unprimed" and "primed" conditions. Pulmonary gas exchange, heart rate, and the electromyogram of m. vastus lateralis were measured during all tests. The phase II VO2 kinetics were slower when severe exercise was initiated from a baseline of moderate exercise compared with unloaded pedaling (mean+/-SD tau, 42+/-15 vs. 33+/-8 s; P0.05). The amplitude of the VO2 slow component and the change in electromyogram from minutes 2 to 6 were both significantly reduced following priming exercise (VO2 slow component: from 0.47+/-0.09 to 0.27+/-0.13 l/min; change in integrated electromyogram between 2 and 6 min: from 51+/-35 to 26+/-43% of baseline; Pchanges in muscle fiber activation.

  20. Kinetics and equilibrium modelling of lead uptake by algae Gelidium and algal waste from agar extraction industry.

    Science.gov (United States)

    Vilar, Vítor J P; Botelho, Cidália M S; Boaventura, Rui A R

    2007-05-08

    Pb(II) biosorption onto algae Gelidium, algal waste from agar extraction industry and a composite material was studied. Discrete and continuous site distribution models were used to describe the biosorption equilibrium at different pH (5.3, 4 and 3), considering competition among Pb(II) ions and protons. The affinity distribution function of Pb(II) on the active sites was calculated by the Sips distribution. The Langmuir equilibrium constant was compared with the apparent affinity calculated by the discrete model, showing higher affinity for lead ions at higher pH values. Kinetic experiments were conducted at initial Pb(II) concentrations of 29-104 mgl(-1) and data fitted to pseudo-first Lagergren and second-order models. The adsorptive behaviour of biosorbent particles was modelled using a batch mass transfer kinetic model, which successfully predicts Pb(II) concentration profiles at different initial lead concentration and pH, and provides significant insights on the biosorbents performance. Average values of homogeneous diffusivity, D(h), are 3.6 x 10(-8); 6.1 x 10(-8) and 2.4 x 10(-8)cm(2)s(-1), respectively, for Gelidium, algal waste and composite material. The concentration of lead inside biosorbent particles follows a parabolic profile that becomes linear near equilibrium.

  1. Kinetics and equilibrium modelling of lead uptake by algae Gelidium and algal waste from agar extraction industry

    International Nuclear Information System (INIS)

    Vilar, Vitor J.P.; Botelho, Cidalia M.S.; Boaventura, Rui A.R.

    2007-01-01

    Pb(II) biosorption onto algae Gelidium, algal waste from agar extraction industry and a composite material was studied. Discrete and continuous site distribution models were used to describe the biosorption equilibrium at different pH (5.3, 4 and 3), considering competition among Pb(II) ions and protons. The affinity distribution function of Pb(II) on the active sites was calculated by the Sips distribution. The Langmuir equilibrium constant was compared with the apparent affinity calculated by the discrete model, showing higher affinity for lead ions at higher pH values. Kinetic experiments were conducted at initial Pb(II) concentrations of 29-104 mg l -1 and data fitted to pseudo-first Lagergren and second-order models. The adsorptive behaviour of biosorbent particles was modelled using a batch mass transfer kinetic model, which successfully predicts Pb(II) concentration profiles at different initial lead concentration and pH, and provides significant insights on the biosorbents performance. Average values of homogeneous diffusivity, D h , are 3.6 x 10 -8 ; 6.1 x 10 -8 and 2.4 x 10 -8 cm 2 s -1 , respectively, for Gelidium, algal waste and composite material. The concentration of lead inside biosorbent particles follows a parabolic profile that becomes linear near equilibrium

  2. Kinetics and equilibrium modelling of lead uptake by algae Gelidium and algal waste from agar extraction industry

    Energy Technology Data Exchange (ETDEWEB)

    Vilar, Vitor J.P. [Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto (Portugal); Botelho, Cidalia M.S. [Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto (Portugal); Boaventura, Rui A.R. [Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Quimica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto (Portugal)]. E-mail: bventura@fe.up.pt

    2007-05-08

    Pb(II) biosorption onto algae Gelidium, algal waste from agar extraction industry and a composite material was studied. Discrete and continuous site distribution models were used to describe the biosorption equilibrium at different pH (5.3, 4 and 3), considering competition among Pb(II) ions and protons. The affinity distribution function of Pb(II) on the active sites was calculated by the Sips distribution. The Langmuir equilibrium constant was compared with the apparent affinity calculated by the discrete model, showing higher affinity for lead ions at higher pH values. Kinetic experiments were conducted at initial Pb(II) concentrations of 29-104 mg l{sup -1} and data fitted to pseudo-first Lagergren and second-order models. The adsorptive behaviour of biosorbent particles was modelled using a batch mass transfer kinetic model, which successfully predicts Pb(II) concentration profiles at different initial lead concentration and pH, and provides significant insights on the biosorbents performance. Average values of homogeneous diffusivity, D {sub h}, are 3.6 x 10{sup -8}; 6.1 x 10{sup -8} and 2.4 x 10{sup -8} cm{sup 2} s{sup -1}, respectively, for Gelidium, algal waste and composite material. The concentration of lead inside biosorbent particles follows a parabolic profile that becomes linear near equilibrium.

  3. Effects of administration route, dietary condition, and blood glucose level on kinetics and uptake of 18F-FDG in mice.

    Science.gov (United States)

    Wong, Koon-Pong; Sha, Wei; Zhang, Xiaoli; Huang, Sung-Cheng

    2011-05-01

    The effects of dietary condition and blood glucose level on the kinetics and uptake of (18)F-FDG in mice were systematically investigated using intraperitoneal and tail-vein injection. Dynamic PET was performed for 60 min on 23 isoflurane-anesthetized male C57BL/6 mice after intravenous (n = 11) or intraperitoneal (n = 12) injection of (18)F-FDG. Five and 6 mice in the intravenous and intraperitoneal groups, respectively, were kept fasting overnight (18 ± 2 h), and the others were fed ad libitum. Serial blood samples were collected from the femoral artery to measure (18)F-FDG and glucose concentrations. Image data were reconstructed using filtered backprojection with CT-based attenuation correction. The standardized uptake value (SUV) was estimated from the 45- to 60-min image. The metabolic rate of glucose (MRGlu) and (18)F-FDG uptake constant (K(i)) were derived by Patlak graphical analysis. In the brain, SUV and K(i) were significantly higher in fasting mice with intraperitoneal injection, but MRGlu did not differ significantly under different dietary states and administration routes. Cerebral K(i) was inversely related to elevated blood glucose levels, irrespective of administration route or dietary state. In myocardium, SUV, K(i), and MRGlu were significantly lower in fasting than in nonfasting mice for both routes of injection. Myocardial SUV and K(i) were strongly dependent on the dietary state, and K(i) did not correlate with the blood glucose level. Similar results were obtained for skeletal muscle, although the differences were not as pronounced. Intraperitoneal injection is a valid alternative route, providing pharmacokinetic data equivalent to data from tail-vein injection for small-animal (18)F-FDG PET. Cerebral K(i) varies inversely with blood glucose level, but the measured cerebral MRGlu does not correlate with blood glucose level or dietary condition. Conversely, the K(i) values of the myocardium and skeletal muscle are strongly dependent on

  4. Kinetic, Thermodynamic and Equilibrium Studies on Uptake of Rhodamine B onto ZnCl2 Activated Low Cost Carbon

    Directory of Open Access Journals (Sweden)

    N. Bhadusha

    2012-01-01

    Full Text Available A carbonaceous adsorbent prepared from biomass waste like wood apple outer shell (Limonia acidissima by ZnCl2 treatment was investigated for its efficiency in removing Rhodamine B (RDB. Influence of agitation time, adsorbent dose, dye concentration, pH and temperature were explored. Two theoretical adsorption isotherms namely Langmuir and Freundlich were used to describe the experimental results. The Langmuir adsorption capacity (Qo was found to be 46.7 mg/g and the equilibrium parameter (RL values indicate favourable adsorption. The experimental data were well fitted with Langmuir isotherm model and pseudo second order kinetic model. Desorption studies showed that ion exchange mechanism might be involved in the adsorption process.

  5. Heterotrophic and mixotrophic growth of Micractinium pusillum Fresenius in the presence of acetate and glucose: effect of light and acetate gradient concentration.

    Science.gov (United States)

    Bouarab, L; Dauta, A; Loudiki, M

    2004-06-01

    The main objective of this study was to determine the importance of secondary mechanism of organic carbon utilization (mixotrophic and heterotrophic modes) in addition to CO2 fixation (photoautotrophic mode) in the green alga, Micractinium pusillum Fresenius (chlorophyta), isolated from a waste stabilization pond. The growth was studied in the presence of acetate and glucose. The incorporation rate of 14C- acetate was measured in the light and in the dark at different concentrations. Finally, in order to underline the role of photosynthesis and respiration processes in the acetate assimilation, the effect of two specific metabolic inhibitors, a specific inhibitor of photosystem II (DCMU) and an uncoupler respiratory (DNP), has been studied. The obtained results showed that M. pusillum grows in the presence of organic substrates, i.e., glucose and acetate, in the light (mixotrophic growth) as well as in the dark (Heterotrophic growth). The growth was much more important in the light than in the dark and more in the presence of glucose than of acetate. In the light, the presence of acetate led to a variation of growth parameters mumax, iotaopt, and beta. The effect of acetate gradient on the growth of the microalga was severe as soon as its concentration in the medium was higher. The acetate uptake followed a Michaelis-Menten kinetic in the light as well as in the dark. The capacity of assimilation was slightly higher in the dark. The utilization of DNP and DCMU indicates that acetate incorporation is an active process depending on both anabolic (photosynthesis) and catabolic (respiration) metabolisms, corroborating the model of the Michaelis-Menten kinetic.

  6. Environmentally relevant organophosphate triesters in herring gulls: In vitro biotransformation and kinetics and diester metabolite formation using a hepatic microsomal assay

    International Nuclear Information System (INIS)

    Greaves, Alana K.; Su, Guanyong; Letcher, Robert J.

    2016-01-01

    The in vitro biotransformation and kinetics of six organophosphate triester (OPE) flame retardants were investigated in herring gulls (Larus argentatus) from the Great Lakes using a hepatic microsomal metabolism assay. Administration of each individual OPE (tri-n-butyl phosphate (TNBP), tris(2-butoxyethyl) phosphate (TBOEP), triphenyl phosphate (TPHP), triethyl phosphate (TEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and tris(2-chloroisopropyl) phosphate (TCIPP)) to the in vitro assay (concentration range 0.01 to 10 μM) resulted in rapid depletion with the exception of TEP. Following the Michaelis-Menten enzyme kinetics model, a preliminary 2-minute incubation period was used to estimate the V max (± SE) values (i.e., the maximal rate of reaction for a saturated enzyme system), which ranged from 5.0 ± 0.4 (TPHP) to 29 ± 18 pmol/min/mg protein (TBOEP), as well as the K M (± SE) values (i.e., the OPE concentration corresponding to one half of the V max ), which ranged from 9.8 ± 1 (TPHP) to 189 ± 135 nM (TBOEP). Biotransformation assays over a 100-minute incubation period revealed that TNBP was metabolized most rapidly (with a depletion rate of 73 ± 4 pmol/min/mg protein), followed by TBOEP (53 ± 8 pmol/min/mg), TCIPP (27 ± 1 pmol/min/mg), TPHP (22 ± 2 pmol/min/mg) and TDCIPP (8 ± 1 pmol/min/mg). In vitro biotransformation of OP triesters was clearly structure-dependent where non-halogenated alkyl OP triesters were metabolized more rapidly than halogenated alkyl triesters. Halogenated OP triesters were transformed to their respective diesters more efficiently relative to non-halogenated OP triesters. To our knowledge, this is the first study to investigate OP triester metabolism and OP diester formation in an avian or wildlife model system, which is important to understand the fate and biological activity of OPEs in an exposed organism. - Highlights: • The metabolism and kinetics of 6 OPEs were examined in herring gull liver microsomes. • The

  7. Physiological and functional diversity of phenol degraders isolated from phenol-grown aerobic granules: Phenol degradation kinetics and trichloroethylene co-metabolic activities.

    Science.gov (United States)

    Zhang, Yi; Tay, Joo Hwa

    2016-03-15

    Aerobic granule is a novel form of microbial aggregate capable of degrading toxic and recalcitrant substances. Aerobic granules have been formed on phenol as the growth substrate, and used to co-metabolically degrade trichloroethylene (TCE), a synthetic solvent not supporting aerobic microbial growth. Granule formation process, rate limiting factors and the comprehensive toxic effects of phenol and TCE had been systematically studied. To further explore their potential at the level of microbial population and functions, phenol degraders were isolated and purified from mature granules in this study. Phenol and TCE degradation kinetics of 15 strains were determined, together with their TCE transformation capacities and other physiological characteristics. Isolation in the presence of phenol and TCE exerted stress on microbial populations, but the procedure was able to preserve their diversity. Wide variation was found with the isolates' kinetic behaviors, with the parameters often spanning 3 orders of magnitude. Haldane kinetics described phenol degradation well, and the isolates exhibited actual maximum phenol-dependent oxygen utilization rates of 9-449 mg DO g DW(-1) h(-1), in phenol concentration range of 4.8-406 mg L(-1). Both Michaelis-Menten and Haldane types were observed for TCE transformation, with the actual maximum rate of 1.04-21.1 mg TCE g DW(-1) h(-1) occurring between TCE concentrations of 0.42-4.90 mg L(-1). The TCE transformation capacities and growth yields on phenol ranged from 20-115 mg TCE g DW(-1) and 0.46-1.22 g DW g phenol(-1), respectively, resulting in TCE transformation yields of 10-70 mg TCE g phenol(-1). Contact angles of the isolates were between 34° and 82°, suggesting both hydrophobic and hydrophilic cell surface. The diversity in the isolates is a great advantage, as it enables granules to be versatile and adaptive under different operational conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Environmentally relevant organophosphate triesters in herring gulls: In vitro biotransformation and kinetics and diester metabolite formation using a hepatic microsomal assay

    Energy Technology Data Exchange (ETDEWEB)

    Greaves, Alana K. [Wildlife and Landscape Directorate, Science and Technology Branch, Environment and Climate Change Canada, National Wildlife Research Centre, Carleton University, Ottawa, ON K1A 0H3 (Canada); Department of Chemistry, Carleton University, Ottawa, ON K1S 5B6 (Canada); Su, Guanyong, E-mail: guanyong.su85@gmail.com [Wildlife and Landscape Directorate, Science and Technology Branch, Environment and Climate Change Canada, National Wildlife Research Centre, Carleton University, Ottawa, ON K1A 0H3 (Canada); Department of Chemistry, Carleton University, Ottawa, ON K1S 5B6 (Canada); Letcher, Robert J., E-mail: robert.letcher@canada.ca [Wildlife and Landscape Directorate, Science and Technology Branch, Environment and Climate Change Canada, National Wildlife Research Centre, Carleton University, Ottawa, ON K1A 0H3 (Canada); Department of Chemistry, Carleton University, Ottawa, ON K1S 5B6 (Canada)

    2016-10-01

    The in vitro biotransformation and kinetics of six organophosphate triester (OPE) flame retardants were investigated in herring gulls (Larus argentatus) from the Great Lakes using a hepatic microsomal metabolism assay. Administration of each individual OPE (tri-n-butyl phosphate (TNBP), tris(2-butoxyethyl) phosphate (TBOEP), triphenyl phosphate (TPHP), triethyl phosphate (TEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and tris(2-chloroisopropyl) phosphate (TCIPP)) to the in vitro assay (concentration range 0.01 to 10 μM) resulted in rapid depletion with the exception of TEP. Following the Michaelis-Menten enzyme kinetics model, a preliminary 2-minute incubation period was used to estimate the V{sub max} (± SE) values (i.e., the maximal rate of reaction for a saturated enzyme system), which ranged from 5.0 ± 0.4 (TPHP) to 29 ± 18 pmol/min/mg protein (TBOEP), as well as the K{sub M} (± SE) values (i.e., the OPE concentration corresponding to one half of the V{sub max}), which ranged from 9.8 ± 1 (TPHP) to 189 ± 135 nM (TBOEP). Biotransformation assays over a 100-minute incubation period revealed that TNBP was metabolized most rapidly (with a depletion rate of 73 ± 4 pmol/min/mg protein), followed by TBOEP (53 ± 8 pmol/min/mg), TCIPP (27 ± 1 pmol/min/mg), TPHP (22 ± 2 pmol/min/mg) and TDCIPP (8 ± 1 pmol/min/mg). In vitro biotransformation of OP triesters was clearly structure-dependent where non-halogenated alkyl OP triesters were metabolized more rapidly than halogenated alkyl triesters. Halogenated OP triesters were transformed to their respective diesters more efficiently relative to non-halogenated OP triesters. To our knowledge, this is the first study to investigate OP triester metabolism and OP diester formation in an avian or wildlife model system, which is important to understand the fate and biological activity of OPEs in an exposed organism. - Highlights: • The metabolism and kinetics of 6 OPEs were examined in herring gull liver

  9. Characterizing nutrient uptake kinetics for efficient crop production during Solanum lycopersicum var. cerasiforme Alef. growth in a closed indoor hydroponic system.

    Science.gov (United States)

    Lee, Ju Yeon; Rahman, Arifur; Azam, Hossain; Kim, Hyung Seok; Kwon, Man Jae

    2017-01-01

    A balanced nutrient supply is essential for the healthy growth of plants in hydroponic systems. However, the commonly used electrical conductivity (EC)-based nutrient control for plant cultivation can provide amounts of nutrients that are excessive or inadequate for proper plant growth. In this study, we investigated the kinetics of major and minor nutrient uptake in a nutrient solution during the growth of tomato (Solanum lycopersicum var. cerasiforme Alef.) in a closed hydroponic system. The concentrations of major and minor ions in the nutrient solution were determined by various analytical methods including inductively coupled plasma-optical emission spectroscopy (ICP-OES), ion chromatography (IC), ion specific electrodes, and/or colorimetric methods. The concentrations of the individual nutrient ions were compared with changes in the EC. The EC of the nutrient solution varied according to the different growth stages of tomato plants. Variation in the concentrations of NO3-, SO42-, Mg2+, Ca2+, and K+ was similar to the EC variation. However, in the cases of PO43-, Na+, Cl-, dissolved Fe and Mn, Cu2+, and Zn2+, variation did not correspond with that of EC. These ions were generally depleted (to 0 mg L-1) during tomato growth, suggesting that these specific ions should be monitored individually and their supply increased. Nutrient uptake rates of major ions increased gradually at different growth stages until harvest (from 15 mg L-1 d-1). Saturation indices determined by MINEQL+ simulation and a mineral precipitation experiment demonstrated the potential for amorphous calcium phosphate precipitation, which may facilitate the abiotic adsorptive removal of dissolved Fe, dissolved Mn, Cu2+, and Zn2+.

  10. Temperature sensitivity of extracellular enzyme kinetics in subtropical wetland soils under different nutrient and water level conditions

    Science.gov (United States)

    Goswami, S.; Inglett, K.; Inglett, P.

    2012-12-01

    Microbial extracellular enzymes play an important role in the initial steps of soil organic matter decomposition and are involved in regulating nutrient cycle processes. Moreover, with the recent concern of climate change, microbial extracellular enzymes may affect the functioning (C losses, C sequestration, greenhouse gas emissions, vegetation changes) of different ecosystems. Hence, it is imperative to understand the biogeochemical processes that may be climate change sensitive. Here, we have measured the Michaelis Menten Kinetics [maximal rate of velocity (Vmax) and half-saturation constant (Km)] of 6 enzymes involved in soil organic matter decomposition (phosphatase, phosphodiesterase, β-D-glucosidase, cellobiohydrolase, leucine aminopeptidase, N-Acetyl-β-D glucosaminidase) in different nutrient(P) concentration both aerobically and anaerobically in Everglade water conservation area 2A (F1, F4-slough and U3-slough). Temperature sensitivity of different enzymes is assessed within soil of different P concentrations. We hypothesized that the temperature sensitivity of the enzyme changes with the biogeochemical conditions including water level and nutrient condition. Furthermore, we have tested specific hypothesis that higher P concentration will initiate more C demand for microbes leading to higher Vmax value for carbon processing enzymes in high P site. We found temperature sensitivity of all enzymes for Vmax and Km under both aerobic and anaerobic condition ranges from 0.6 to 3.2 for Vmax and 0.5 to 2.5 for Km. Q10 values of Km for glucosidase indicate more temperature sensitivity under anaerobic condition. Under aerobic condition higher temperature showed significant effect on Vmax for bisphosphatase between high P and low P site. Decreasing P concentration from F1 site to U3-S site had showed significant effect in all temperature on carbon processing enzyme. This suggests that in high P site, microbes will use more carbon-processing enzyme to get more carbon

  11. Kinetic Studies on Trichoderna Viride Cellulase

    International Nuclear Information System (INIS)

    Saw Aung; Oo Aung; Aung Myint

    2002-02-01

    Studies on cellulase enzyme (EC 3.2.1.4), which catalyzes the hydrolysis of. cellulose to yield glucose, were made. Cellulase from a fungus source, Trichoderma viride was cultivated on Czapek's agar medium and enzyme production broth medium was employed for parameter tests. The microscopic examination and cellulase hydrolysis test on subcultured fungi were applied to confirm the T. viride species. A calibration curve for standard glucose was plotted by using visible spectroscopy. Dinitrosalicylic acid was used as enzyme reaction inhibitor and the colour intensity was measured in a UV-visible spectrophotometer at a λ max of 570 nm. The parameters such as optimum pH, optimum temperature, effect of substrate concentration, effect, of enzyme concentration, enzyme unit (EU), reaction order (n), maximum velocity (V max ), Michaelis-Menten constant (K m ) using various substrates, viz., carboxy methylcellulose, cotton fibre and filter paper determined. (author)

  12. Kinetics of [123I]iodide uptake and discharge by perchlorate in studies of inhibition of iodide binding by antithyroid drugs

    International Nuclear Information System (INIS)

    McCruden, D.C.; Connell, J.M.C.; Alexander, W.D.; Hilditch, T.E.

    1985-01-01

    Thyroidal binding of iodide was studied by kinetic analysis of [ 123 ]iodide uptake and its discharge by perchlorate in 80 hyperthyroid subjects receiving antithyroid drug therapy. Five dosage regimens ranging from 5 mg carbimazole twice daily to 15 mg methimazole twice daily were studied. Binding inhibition was estimated at 5-7 h after drug as an index of the mean effect of the 12 hourly regimen. In all cases, except one in the lowest dose group, binding was found to be markedly reduced with mean binding rates ranging from 0.002 to 0.020 min -1 (normal > 0.15 min -1 ). The net clearance of iodide in the lowest dose group was reduced to a mean value near the upper limit of the euthyroid range, whereas in the highest dose group it lay at the lower limit of the euthyroid range. These results were reflected in the serum thyroid hormone response. There was a reducing incidence of inadequate control of hyperthyroidism and an increasing incidence of hypothyroidism with increasing thiourylene dose. The exit rate constant of free iodide for the various doses showed values from 0.048 to 0.055 min -1 . Correpsonding mean values for the discharge rate constant after perchlorate were 0.087 to 0.105 min -1 . This suggests that perchlorate increases the rate of iodide release from the thyroid gland. Studies at a later interval after drug (12-14 h) showed no change in discharge rate constant. This leads to the conclusion that perchlorate may further inhibit iodide binding in subjects receiving antithyroid drug therapy. (author)

  13. Combining Microbial Enzyme Kinetics Models with Light Use Efficiency Models to Predict CO2 and CH4 Ecosystem Exchange from Flooded and Drained Peatland Systems

    Science.gov (United States)

    Oikawa, P. Y.; Jenerette, D.; Knox, S. H.; Sturtevant, C. S.; Verfaillie, J. G.; Baldocchi, D. D.

    2014-12-01

    Under California's Cap-and-Trade program, companies are looking to invest in land-use practices that will reduce greenhouse gas (GHG) emissions. The Sacramento-San Joaquin River Delta is a drained cultivated peatland system and a large source of CO2. To slow soil subsidence and reduce CO2 emissions, there is growing interest in converting drained peatlands to wetlands. However, wetlands are large sources of CH4 that could offset CO2-based GHG reductions. The goal of our research is to provide accurate measurements and model predictions of the changes in GHG budgets that occur when drained peatlands are restored to wetland conditions. We have installed a network of eddy covariance towers across multiple land use types in the Delta and have been measuring CO2 and CH4 ecosystem exchange for multiple years. In order to upscale these measurements through space and time we are using these data to parameterize and validate a process-based biogeochemical model. To predict gross primary productivity (GPP), we are using a simple light use efficiency (LUE) model which requires estimates of light, leaf area index and air temperature and can explain 90% of the observed variation in GPP in a mature wetland. To predict ecosystem respiration we have adapted the Dual Arrhenius Michaelis-Menten (DAMM) model. The LUE-DAMM model allows accurate simulation of half-hourly net ecosystem exchange (NEE) in a mature wetland (r2=0.85). We are working to expand the model to pasture, rice and alfalfa systems in the Delta. To predict methanogenesis, we again apply a modified DAMM model, using simple enzyme kinetics. However CH4 exchange is complex and we have thus expanded the model to predict not only microbial CH4 production, but also CH4 oxidation, CH4 storage and the physical processes regulating the release of CH4 to the atmosphere. The CH4-DAMM model allows accurate simulation of daily CH4 ecosystem exchange in a mature wetland (r2=0.55) and robust estimates of annual CH4 budgets. The LUE

  14. The single-process biochemical reaction of Rubisco: a unified theory and model with the effects of irradiance, CO₂ and rate-limiting step on the kinetics of C₃ and C₄ photosynthesis from gas exchange.

    Science.gov (United States)

    Farazdaghi, Hadi

    2011-02-01

    Photosynthesis is the origin of oxygenic life on the planet, and its models are the core of all models of plant biology, agriculture, environmental quality and global climate change. A theory is presented here, based on single process biochemical reactions of Rubisco, recognizing that: In the light, Rubisco activase helps separate Rubisco from the stored ribulose-1,5-bisphosphate (RuBP), activates Rubisco with carbamylation and addition of Mg²(+), and then produces two products, in two steps: (Step 1) Reaction of Rubisco with RuBP produces a Rubisco-enediol complex, which is the carboxylase-oxygenase enzyme (Enco) and (Step 2) Enco captures CO₂ and/or O₂ and produces intermediate products leading to production and release of 3-phosphoglycerate (PGA) and Rubisco. PGA interactively controls (1) the carboxylation-oxygenation, (2) electron transport, and (3) triosephosphate pathway of the Calvin-Benson cycle that leads to the release of glucose and regeneration of RuBP. Initially, the total enzyme participates in the two steps of the reaction transitionally and its rate follows Michaelis-Menten kinetics. But, for a continuous steady state, Rubisco must be divided into two concurrently active segments for the two steps. This causes a deviation of the steady state from the transitional rate. Kinetic models are developed that integrate the transitional and the steady state reactions. They are tested and successfully validated with verifiable experimental data. The single-process theory is compared to the widely used two-process theory of Farquhar et al. (1980. Planta 149, 78-90), which assumes that the carboxylation rate is either Rubisco-limited at low CO₂ levels such as CO₂ compensation point, or RuBP regeneration-limited at high CO₂. Since the photosynthesis rate cannot increase beyond the two-process theory's Rubisco limit at the CO₂ compensation point, net photosynthesis cannot increase above zero in daylight, and since there is always respiration at

  15. Physiological Response of Plants Grown on Porous Ceramic Tubes

    Science.gov (United States)

    Tsao, David; Okos, Martin

    1997-01-01

    This research involves the manipulation of the root-zone water potential for the purposes of discriminating the rate limiting step in the inorganic nutrient uptake mechanism utilized by higher plants. This reaction sequence includes the pathways controlled by the root-zone conditions such as water tension and gradient concentrations. Furthermore, plant based control mechanisms dictated by various protein productions are differentiated as well. For the nutrients limited by the environmental availability, the kinetics were modeled using convection and diffusion equations. Alternatively, for the nutrients dependent upon enzyme manipulations, the uptakes are modeled using Michaelis-Menten kinetics. In order to differentiate between these various mechanistic steps, an experimental apparatus known as the Porous Ceramic Tube - Nutrient Delivery System (PCT-NDS) was used. Manipulation of the applied suction pressure circulating a nutrient solution through this system imposes a change in the matric component of the water potential. This compensates for the different osmotic components of water potential dictated by nutrient concentration. By maintaining this control over the root-zone conditions, the rate limiting steps in the uptake of the essential nutrients into tomato plants (Lycopersicon esculentum cv. Cherry Elite) were differentiated. Results showed that the uptake of some nutrients were mass transfer limited while others were limited by the enzyme kinetics. Each of these were adequately modeled with calculations and discussions of the parameter estimations provided.

  16. Studies on the influence of the interval after blood withdrawal and different storage temperatures on the uptake and kinetics of 14C-serotonin in human thrombocytes in vitro

    International Nuclear Information System (INIS)

    Jarosch, U.

    1978-07-01

    The active in-vitro uptake of 14 C-serotonin in human thrombocytes was investigated in dependence of the interval after blood withdrawal (10-130 min) and the storage temperature of the platelet-rich plasma (4 0 , 22 0 , 37 0 C) for different incubation periods (2, 5, 10 minutes at 37 0 C). The kinetic study of 14 C serotonin uptake showed a constant affinity to the thrombocyte serotonin transport system for all experimental conditions while the maximum reaction rate was clearly affected. One exception was the value determined after 130 minutes of storage time and a storage temperature of 37 0 C for a 14 C serotonin concentration of 10 -5 M which showed a reduced affinity. (orig./AJ) [de

  17. Muscular and pulmonary O2 uptake kinetics during moderate- and high-intensity sub-maximal knee-extensor exercise in humans

    DEFF Research Database (Denmark)

    Krustrup, Peter; Jones, Andrew M.; Wilkerson, Daryl P.

    2009-01-01

    artery to vein and vein to artery). The kinetics of m O2 and p O2 were modelled using non-linear regression. The time constant (tau) describing the phase II p O2 kinetics following the onset of exercise was not significantly different from the mean response time (initial time delay + &tgr) for m O2...... kinetics for LI (30 +/- 3 vs. 30 +/- 3 s) but was slightly higher (P....05; r = -0.01) and HI (33 +/- 3 vs. 27 +/- 3, P>0.05; r = -0.04). MTT was ~17 s just before exercise and decreased to 10 s and 12 s after 5 s of exercise for LI and HI, respectively. These data indicate that the phase II p O2 kinetics reflect m O2 kinetics during exercise but not during recovery where...

  18. Extraction of Crude Chitinase from Higher Plants and their Chitin-Hydrolysis Activities; Kotosyokubutu yurai kichinaze no chusyutu to kichin bunkai kassei

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, K.; Harada, K.; Shibata, M.; Maeda, R. [Doshisha Univ., Kyoto (Japan). Faculty of Engineering

    1997-07-10

    To prepare a purified chitinase from higher plants, firstly, crude enzymes were extracted from six higher plants, namely, radish seeds, sunflower seeds, watermelon seeds, bamboo leaves, orange skin, and persimmon skin. Using these crude enzymes, pH dependencies of hydrolysis reaction of colloidal chitin are investigated. For radish seeds and bamboo leaves, which have relatively high activities, the kinetics of enzymatic reaction are studies. It is clear that these reactions obey Michaelis-Menten kinetics. 7 refs., 3 figs., 2 tabs.

  19. Para-[{sup 123}I]iodo-L-phenylalanine in patients with pancreatic adenocarcinoma. Tumour uptake, whole-body kinetics, dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Hellwig, D.; Gouverneur, E.; Schaefer, A.; Kirsch, C.M.; Samnick, S. [Dept. of Nuclear Medicine, Saarland Univ. Medical Center, Homburg (Germany); Raedle, J.; Menges, M. [Dept. of Internal Medicine II (Gastroenterology), Saarland Univ. Medical Center, Homburg (Germany)

    2008-07-01

    Recently, p-[{sup 123}I]iodo-L-phenylalanine (IPA) was clinically validated for brain tumour imaging. Preclinical studies demonstrated uptake of IPA into pancreatic adenocarcinoma suggesting its diagnostic application in patients with pancreatic tumours. The aim was to study the tumour uptake of IPA in patients with pancreatic adenocarcinoma and to analyse its biodistribution and dosimetry to assess the radiation dose resulting from its diagnostic use. Patients, methods: Seven patients with pancreatic adenocarcinoma underwent whole-body scintigraphies and SPECT up to 24 h after administration of 250 MBq of IPA. Tumour uptake of IPA was assessed visually. Time activity curves and the corresponding residence times were determined for whole-body, kidneys, liver, spleen, lung, heart content, brain, and testes. Mean absorbed doses for various organs and the effective dose were assessed based on the MIRD formalism using OLINDA/EXM. Results: IPA exhibited no accumulation in proven manifestations of pancreatic adenocarcinomas. IPA was exclusively eliminated by the urine and showed a delayed clearance from blood. Residence times were 0.26 {+-} 0.09 h for kidneys, 0.38 {+-} 0.19 h for liver, 0.15 {+-} 0.07 h for spleen, 0.51 {+-} 0.20 h for lungs, 0.22 {+-} 0.07 h for heart content, 0.11 {+-} 0.05 h for brain, 0.014 {+-} 0.005 h for testes and 6.4 {+-} 2.2 h for the remainder. The highest absorbed doses were determined in the urinary bladder wall and in the kidneys. According to the ICRP 60 the effective dose resulting from 250 MBq IPA was 3.6 {+-} 0.7 mSv. Conclusion: Para-[{sup 123}I]iodo-L-phenylalanine can be used in diagnostic nuclear medicine with acceptable radiation doses. Besides its proven validity for brain tumour imaging, IPA does not appear to be suitable as tracer for pancreatic cancer. (orig.)

  20. A two-compartment description and kinetic procedure for measuring regional cerebral [11C]nomifensine uptake using positron emission tomography

    International Nuclear Information System (INIS)

    Salmon, E.; Brooks, D.J.; Leenders, K.L.; Turton, D.R.; Hume, S.P.; Cremer, J.E.; Jones, T.; Frackowiak, R.S.

    1990-01-01

    S-[11C]Nomifensine (S-[11C]NMF) is a positron-emitting tracer suitable for positron emission tomography, which binds to both dopaminergic and noradrenergic reuptake sites in the striatum and the thalamus. Modelling of the cerebral distribution of this drug has been hampered by the rapid appearance of glucuronide metabolites in the plasma, which do not cross the blood--brain barrier. To date, [11C]NMF uptake has simply been expressed as regional versus nonspecific cerebellar activity ratios. We have calculated a free NMF input curve from red cell activity curves, using the fact that the free drug rapidly equilibrates between red cells and plasma, while glucuronides do not enter red cells. With this free [11C]NMF input function, all regional cerebral uptake curves could be fitted to a conventional two-compartment model, defining tracer distribution in terms of [11C]NMF regional volume of distribution. Assuming that the cerebellar volume of distribution of [11C]NMF represents the nonspecific volume of distribution of the tracer in striatum and thalamus, we have calculated an equilibrium partition coefficient for [11C]NMF between freely exchanging specific and nonspecific compartments in these regions, representing its binding potential to dopaminergic or noradrenergic uptake sites (or complexes). This partition coefficient was lower in the striatum when the racemate rather than the active S-enantiomer of [11C]NMF was administered. In the striatum of patients suffering from Parkinson's disease and multiple-system atrophy, the specific compartmentation of S-[11C]NMF was significantly decreased compared with that of age-matched volunteers

  1. Kinetic studies of the acylation of pig muscle–d-glyceraldehyde 3-phosphate dehydrogenase by 1,3-diphosphoglycerate and of proton uptake and release in the overall enzyme mechanism

    Science.gov (United States)

    Harrigan, P. J.; Trentham, D. R.

    1973-01-01

    In the presence of NAD+ the acylation by 1,3-diphosphoglycerate of the four active sites of pig muscle d-glyceraldehyde 3-phosphate dehydrogenase can be monitored at 365nm by the disappearance of the absorption band present in the binary complex of NAD+ and the enzyme. A non-specific salt effect decreased the acylation rate 25-fold when the ionic strength was increased from 0.10 to 1.0. This caused acylation to be the rate-limiting process in the enzyme-catalysed reductive dephosphorylation of 1,3-diphosphoglycerate at high ionic strength at pH8. The salt effect permitted investigation of the acylation over a wide range of conditions. Variation of pH from 5.4 to 8.6 produced at most a two-fold change in the acylation rate. One proton was taken up per site acylated at pH8.0. By using a chromophoric H+ indicator the rate of proton uptake could be monitored during the acylation and was also almost invariant in the pH range 5.5–8.5. Transient kinetic studies of the overall enzyme-catalysed reaction indicated that acylation was the process involving proton uptake at pH8.0. The enzyme mechanism is discussed in the light of these results. PMID:4360248

  2. Quantifying the relative contributions of different solute carriers to aggregate substrate transport

    Science.gov (United States)

    Taslimifar, Mehdi; Oparija, Lalita; Verrey, Francois; Kurtcuoglu, Vartan; Olgac, Ufuk; Makrides, Victoria

    2017-01-01

    Determining the contributions of different transporter species to overall cellular transport is fundamental for understanding the physiological regulation of solutes. We calculated the relative activities of Solute Carrier (SLC) transporters using the Michaelis-Menten equation and global fitting to estimate the normalized maximum transport rate for each transporter (Vmax). Data input were the normalized measured uptake of the essential neutral amino acid (AA) L-leucine (Leu) from concentration-dependence assays performed using Xenopus laevis oocytes. Our methodology was verified by calculating Leu and L-phenylalanine (Phe) data in the presence of competitive substrates and/or inhibitors. Among 9 potentially expressed endogenous X. laevis oocyte Leu transporter species, activities of only the uniporters SLC43A2/LAT4 (and/or SLC43A1/LAT3) and the sodium symporter SLC6A19/B0AT1 were required to account for total uptake. Furthermore, Leu and Phe uptake by heterologously expressed human SLC6A14/ATB0,+ and SLC43A2/LAT4 was accurately calculated. This versatile systems biology approach is useful for analyses where the kinetics of each active protein species can be represented by the Hill equation. Furthermore, its applicable even in the absence of protein expression data. It could potentially be applied, for example, to quantify drug transporter activities in target cells to improve specificity. PMID:28091567

  3. Competition between roots and microorganisms for nitrogen: mechanisms and ecological relevance

    Science.gov (United States)

    Kuzyakov, Yakov; Xu, Xingliang

    2014-05-01

    Demand of all living organisms on the same nutrients forms the basis for interspecific competition between plants and microorganisms in soils. This competition is especially strong in the rhizosphere. To evaluate competitive and mutualistic interactions between plants and microorganisms and to analyse ecological consequences of these interactions, we analysed 424 data pairs from 41 15N-labelling studies that investigated 15N redistribution between roots and microorganisms. Calculated Michaelis-Menten kinetics based on Km (Michaelis constant) and Vmax (maximum uptake capacity) values from 77 studies on the uptake of nitrate, ammonia, and amino acids by roots and microorganisms clearly showed that, shortly after nitrogen (N) mobilization from soil organic matter and litter, microorganisms take up most N. Lower Km values of microorganisms suggest that they are especially efficient at low N concentrations, but can also acquire more N at higher N concentrations (Vmax) compared with roots. Because of the unidirectional flow of nutrients from soil to roots, plants are the winners for N acquisition in the long run. Therefore, despite strong competition between roots and microorganisms for N, a temporal niche differentiation reflecting their generation times leads to mutualistic relationships in the rhizosphere. This temporal niche differentiation is highly relevant ecologically because it: protects ecosystems from N losses by leaching during periods of slow or no root uptake; continuously provides roots with available N according to plant demand; and contributes to the evolutionary development of mutualistic interactions between roots and microorganisms.

  4. Influence of extreme pedal rates on pulmonary O(2) uptake kinetics during transitions to high-intensity exercise from an elevated baseline.

    Science.gov (United States)

    Dimenna, Fred J; Wilkerson, Daryl P; Burnley, Mark; Bailey, Stephen J; Jones, Andrew M

    2009-10-31

    We used extreme pedal rates to investigate the influence of muscle fibre recruitment on pulmonary V(O)(2) kinetics during unloaded-to-moderate-intensity (U-->M), unloaded-to-high-intensity (U-->H), and moderate-intensity to high-intensity (M-->H) cycling transitions. Seven healthy men completed transitions to 60% of the difference between gas-exchange threshold and peak V(O)(2) from both an unloaded and a moderate-intensity (95% GET) baseline at cadences of 35 and 115rpm. Pulmonary gas exchange was measured breath-by-breath and iEMG of the m. vastus lateralis and m. gluteus maximus was measured during all tests. At 35rpm, the phase II time constant (tau(p)) values for U-->M, U-->H, and M-->H were 26+/-7, 31+/-7 and 36+/-8s with the value for M-->H being longer than for U-->M (PM, U-->H, and M-->H were 29+/-8, 48+/-16 and 53+/-20s with the value for U-->M being shorter than for the other two conditions (Pinfluenced by an interaction of exercise intensity and pedal rate and are consistent with the notion that changes in muscle fibre recruitment are responsible for slower phase II V(O)(2) kinetics during high-intensity and work-to-work exercise transitions.

  5. Testing the behaviour of different kinetic models for uptake/release of radionuclides between water and sediments when implemented in a marine dispersion model

    International Nuclear Information System (INIS)

    Perianez, R.

    2004-01-01

    Three kinetic models for adsorption/release of 137 Cs between water and sediments have been tested when they are included in a previously validated dispersion model of the English Channel. Radionuclides are released to the Channel from La Hague nuclear fuel reprocessing plant (France). The kinetic models are a 1-step model consisting of a single reversible reaction, a 2-step model consisting of two consecutive reversible reactions and an irreversible model consisting of three parallel reactions: two reversible and one irreversible. The models have been tested under three typical situations that correspond to the source terms that can generally be found: instantaneous release, continuous release and redissolution of radionuclides from contaminated sediments. Differences between the models become more evident when contact times between water and sediments are larger (continuous release) and in the case of redissolution from sediments. Time scales for the redissolution process are rather different between the three models. The 1-step model produces a redissolution that is too fast when compared with experimental evidence. The irreversible model requires that saturation effects of the irreversible phase are included. Probably, the 2-step model represents the best compromise between ease and level of detail of the description of sorption/release processes

  6. Biosorptive uptake of Fe2+, Cu2+ and As5+ by activated biochar derived from Colocasia esculenta: Isotherm, kinetics, thermodynamics, and cost

    Directory of Open Access Journals (Sweden)

    Soumya Banerjee

    2016-09-01

    Full Text Available The adsorptive capability of superheated steam activated biochar (SSAB produced from Colocasia esculenta was investigated for removal of Cu2+, Fe2+ and As5+ from simulated coal mine wastewater. SSAB was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer–Emmett–Teller analyser. Adsorption isotherm indicated monolayer adsorption which fitted best in Langmuir isotherm model. Thermodynamic study suggested the removal process to be exothermic, feasible and spontaneous in nature. Adsorption of Fe2+, Cu2+ and As5+ on to SSAB was found to be governed by pseudo-second order kinetic model. Efficacy of SSAB in terms of metal desorption, regeneration and reusability for multiple cycles was studied. Regeneration of metal desorbed SSAB with 1 N sodium hydroxide maintained its effectiveness towards multiple metal adsorption cycles. Cost estimation of SSAB production substantiated its cost effectiveness as compared to commercially available activated carbon. Hence, SSAB could be a promising adsorbent for metal ions removal from aqueous solution.

  7. Uptake and elimination kinetics of perfluoroalkyl substances in submerged and free-floating aquatic macrophytes: Results of mesocosm experiments with Echinodorus horemanii and Eichhornia crassipes.

    Science.gov (United States)

    Pi, N; Ng, J Z; Kelly, B C

    2017-06-15

    Studies investigating the bioaccumulation behavior of perfluoroalkyl substances (PFASs) in aquatic macrophytes are limited. The present study involved controlled mesocosm experiments to assess uptake and elimination rate constants (k u, k e ), bioconcentration factors (BCFs) and translocation factors (TFs) of several perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkane sulfonic acids (PFSAs) in two aquatic plant species, including one submerged species (Echinodorus horemanii) and one free-floating species (Eichhornia crassipes). The results indicated all PFASs were readily accumulated in these aquatic macrophytes. k u and BCFs increased with increasing perfluoroalkyl chain length. For PFCAs and PFSAs with identical perfluoroalkyl chain length, the corresponding PFSA exhibited higher bioaccumulation potential. On a whole-plant basis, the bioaccumulation potential of PFASs in submerged and free-floating macrophytes were comparable, indicating sorption to plant biomass is similar in the different species. Conversely, when considering accumulation in foliage, BCFs in the free-floating macrophyte were substantially lower compared to submerged species, especially for longer-chain PFASs. Compounds with shorter perfluoroalkyl chain length (PFBS, PFPeA and PFHxA) exhibited preferential translocation to leaf tissue (TFs >1). BCFs exhibited a sigmoidal relationship with pefluoroalkyl chain length, membrane-water distribution coefficients (D mw ), protein-water distribution coefficients (D pw ) and organic-water partition coefficients (K oc ). For these trends, maximum BCF values were exhibited by long-chain PFCAs, with a log D mw , log D pw and log K oc of 6.47, 5.72 and 5.04, respectively. These findings are useful for future design and implementation of phytoremediation systems, as well for future develop of mechanistic models for predicting the environmental fate and distribution of these contaminants of concern. Copyright © 2017. Published by Elsevier Ltd.

  8. Characterization of inorganic phosphate transport in the triple-negative breast cancer cell line, MDA-MB-231.

    Science.gov (United States)

    Russo-Abrahão, Thais; Lacerda-Abreu, Marco Antônio; Gomes, Tainá; Cosentino-Gomes, Daniela; Carvalho-de-Araújo, Ayra Diandra; Rodrigues, Mariana Figueiredo; Oliveira, Ana Carolina Leal de; Rumjanek, Franklin David; Monteiro, Robson de Queiroz; Meyer-Fernandes, José Roberto

    2018-01-01

    Recent studies demonstrate that interstitial inorganic phosphate is significantly elevated in the breast cancer microenvironment as compared to normal tissue. In addition it has been shown that breast cancer cells express high levels of the NaPi-IIb carrier (SLC34A2), suggesting that this carrier may play a role in breast cancer progression. However, the biochemical behavior of inorganic phosphate (Pi) transporter in this cancer type remains elusive. In this work, we characterize the kinetic parameters of Pi transport in the aggressive human breast cancer cell line, MDA-MB-231, and correlated Pi transport with cell migration and adhesion. We determined the influence of sodium concentration, pH, metabolic inhibitors, as well as the affinity for inorganic phosphate in Pi transport. We observed that the inorganic phosphate is dependent on sodium transport (K0,5 value = 21.98 mM for NaCl). Furthermore, the transport is modulated by different pH values and increasing concentrations of Pi, following the Michaelis-Menten kinetics (K0,5 = 0.08 mM Pi). PFA, monensin, furosemide and ouabain inhibited Pi transport, cell migration and adhesion. Taken together, these results showed that the uptake of Pi in MDA-MB-231 cells is modulated by sodium and by regulatory mechanisms of intracellular sodium gradient. General Significance: Pi transport might be regarded as a potential target for therapy against tumor progression.

  9. Hepatic taurine transport: a Na+-dependent carrier on the basolateral plasma membrane

    International Nuclear Information System (INIS)

    Bucuvalas, J.C.; Goodrich, A.L.; Suchy, F.J.

    1987-01-01

    Highly purified rat basolateral liver plasma membrane vesicles were used examine the mechanism and the driving forces for hepatic uptake of the β-amino acid, taurine. An inwardly directed 100 mM NaCl gradient stimulated the initial rate of taurine uptake and energized a transient twofold accumulation of taurine above equilibrium (overshoot). In contrast, uptake was slower and no overshoot was detected in the presence of a KCl gradient. A negative intravesicular electrical potential generated by the presence of permeant anions or an outwardly directed K + gradient with valinomycin increased Na + -stimulated taurine uptake. External Cl - stimulated Na + -dependent taurine uptake independent of effects on the transmembrane electrical potential difference. Na + -dependent taurine uptake showed a sigmoidal dependence on extravesicular Na + concentration, suggesting multiple Na + ions are involved in the translocation of each taurine molecule. Na + -dependent taurine uptake demonstrated Michaelis-Menten kinetics with a maximum velocity of 0.537 nmol x mg protein -1 x min -1 and an apparent K/sub m/ of 174 μM. [ 3 H]taurine uptake was inhibited by the presence of excess unlabeled taurine, β-alanine, or hypotaurine but not by L-glutamine or L-alanine. In summary, using basolateral liver plasma membrane vesicles, the authors have shown that hepatic uptake of taurine occurs by a carrier-mediated, secondary active transport process specific for β-amino acids. Uptake is electrogenic, stimulated by external Cl - , and requires multiple Na + ions for the translocation of each taurine molecule

  10. Exploring the controls of soil biogeochemistry in a restored coastal wetland using object-oriented computer simulations of uptake kinetics and thermodynamic optimization in batch reactors

    Science.gov (United States)

    Payn, R. A.; Helton, A. M.; Poole, G.; Izurieta, C.; Bernhardt, E. S.; Burgin, A. J.

    2012-12-01

    Many hypotheses have been proposed to predict patterns of biogeochemical redox reactions based on the availability of electron donors and acceptors and the thermodynamic theory of chemistry. Our objective was to develop a computer model that would allow us to test various alternatives of these hypotheses against data gathered from soil slurry batch reactors, experimental soil perfusion cores, and in situ soil profile observations from the restored Timberlake Wetland in coastal North Carolina, USA. Software requirements to meet this objective included the ability to rapidly develop and compare different hypothetical formulations of kinetic and thermodynamic theory, and the ability to easily change the list of potential biogeochemical reactions used in the optimization scheme. For future work, we also required an object pattern that could easily be coupled with an existing soil hydrologic model. These requirements were met using Network Exchange Objects (NEO), our recently developed object-oriented distributed modeling framework that facilitates simulations of multiple interacting currencies moving through network-based systems. An initial implementation of the object pattern was developed in NEO based on maximizing growth of the microbial community from available dissolved organic carbon. We then used this implementation to build a modeling system for comparing results across multiple simulated batch reactors with varied initial solute concentrations, varied biogeochemical parameters, or varied optimization schemes. Among heterotrophic aerobic and anaerobic reactions, we have found that this model reasonably predicts the use of terminal electron acceptors in simulated batch reactors, where reactions with higher energy yields occur before reactions with lower energy yields. However, among the aerobic reactions, we have also found this model predicts dominance of chemoautotrophs (e.g., nitrifiers) when their electron donor (e.g., ammonium) is abundant, despite the

  11. Kinetic evaluation of an anaerobic fluidised-bed reactor treating slaughterhouse wastewater

    Energy Technology Data Exchange (ETDEWEB)

    Borja, R. [Consejo Superior de Investigaciones Cientificas, Seville (Spain). Inst. de la Grasa; Banks, C.J.; Zhengjian Wang [Manchester Univ. (United Kingdom). Inst. of Science and Technology

    1995-09-01

    An anaerobic fluidised-bed reactor for purification of slaughterhouse wastewater was modelled as a continuous-flow, completely-mixed homogeneous microbial system, with the feed COD as the limiting-substrate concentration. The average microbial residence time in the reactor was defined in terms of conventional sludge-retention-time. The experimental data obtained indicated that the Michaelis-Menten expression was applicable to a description of substrate utilisation (i.e. COD removal) in the anaerobic fluidised-bed system. The maximum substrate utilisation rate, k, and the Michaelis constant, K{sub s}, were determined to be 1.2/day and 0.039 g/l. The observed biomass yield in the reactor decreased with increasing sludge-retention-time. The specific methane production rate observed was a linear function of the specific substrate-utilisation rate. (Author)

  12. Cell uptake survey of pegylated nanographene oxide.

    Science.gov (United States)

    Vila, M; Portolés, M T; Marques, P A A P; Feito, M J; Matesanz, M C; Ramírez-Santillán, C; Gonçalves, G; Cruz, S M A; Nieto, A; Vallet-Regi, M

    2012-11-23

    Graphene and more specifically, nanographene oxide (GO) has been proposed as a highly efficient antitumoral therapy agent. Nevertheless, its cell uptake kinetics, its influence in different types of cells and the possibility of controlling cellular internalization timing, is still a field that remains unexplored. Herein, different cell types have been cultured in vitro for several incubation periods in the presence of 0.075 mg ml(-1) pegylated GO solutions. GO uptake kinetics revealed differences in the agent's uptake amount and speed as a function of the type of cell involved. Osteoblast-like cells GO uptake is higher and faster without resulting in greater cell membrane damage. Moreover, the dependence on the commonly used PEG nature (number of branches) also influences the viability and cell uptake speed. These facts play an important role in the future definition of timing parameters and selective cell uptake control in order to achieve an effective therapy.

  13. Cell uptake survey of pegylated nanographene oxide

    International Nuclear Information System (INIS)

    Vila, M; Nieto, A; Vallet-Regi, M; Portolés, M T; Feito, M J; Matesanz, M C; Ramírez-Santillán, C; Marques, P A A P; Gonçalves, G; Cruz, S M A

    2012-01-01

    Graphene and more specifically, nanographene oxide (GO) has been proposed as a highly efficient antitumoral therapy agent. Nevertheless, its cell uptake kinetics, its influence in different types of cells and the possibility of controlling cellular internalization timing, is still a field that remains unexplored. Herein, different cell types have been cultured in vitro for several incubation periods in the presence of 0.075 mg ml −1 pegylated GO solutions. GO uptake kinetics revealed differences in the agent’s uptake amount and speed as a function of the type of cell involved. Osteoblast-like cells GO uptake is higher and faster without resulting in greater cell membrane damage. Moreover, the dependence on the commonly used PEG nature (number of branches) also influences the viability and cell uptake speed. These facts play an important role in the future definition of timing parameters and selective cell uptake control in order to achieve an effective therapy. (paper)

  14. Development and validation of an antigen-binding capture ELISA for native and putrescine-modified anti-tetanus F(ab')2 fragments for the assessment of the cellular uptake and plasma kinetics of the antibodies.

    Science.gov (United States)

    Welfringer, Frédéric; d'Athis, Philippe; Scherrmann, Jean-Michel; Hervé, Françoise

    2005-12-20

    Cationization is a strategy to enhance the permeability of antibodies to physiological membranes for potential therapeutic and diagnostic applications of these proteins, with one of its crucial points being the retention of antigen binding activity. Here, we describe the cationization of horse polyclonal anti-tetanus F(ab')(2) fragments and the development and validation of an ELISA for quantitative measurements of the binding activity of the native and cationized F(ab')(2) in cell lysates and rat plasma samples, assessing the cellular uptake and plasma kinetics of these antibodies, respectively. The method used tetanus anatoxin coated on microtitre plates as capture antigen to bind sample or standard F(ab')(2), the amount of antibody binding being quantified using, first, a secondary biotinylated anti-horse antibody/streptavidin-alkaline phosphatase complex in situ and then a measurement of the substrate product. Cationization of the F(ab')(2) was performed with putrescine at pH 4.5 using soluble carbodiimide as carboxyl activator. The average substitution ratio was determined at 3 putrescine molecules per F(ab')(2) molecule. The cationized F(ab')(2) retained roughly 80% of the initial antigen binding activity and was stable over a 1 year period of storage at -20 degrees C. The ELISA validation data showed that the method was linear for both the native and cationized F(ab')(2) using Hanks' balanced saline solution with 0.2% bovine serum albumin as assay diluent for the cell lysate samples. The useful F(ab')(2) concentration range was 2.5-25 ng/ml and the limit of quantification was 2.5 ng/ml. With rat blank plasma used as assay diluent for the rat plasma samples the useful F(ab')(2) concentration range was 3.5-25 ng/ml and the limit of quantification was 3.5 ng/ml. Specific requirements for the limits of quantification were fulfilled: precision tetanus F(ab')(2) in an HL 60 cell model, and of plasma kinetics after i.v. administration to rats.

  15. A Critical View on In Vitro Analysis of P-glycoprotein (P-gp) Transport Kinetics

    DEFF Research Database (Denmark)

    Saaby, Lasse; Brodin, Birger

    2017-01-01

    Transport proteins expressed in the different barriers of the human body can have great implications on absorption, distribution, and excretion of drug compounds. Inhibition or saturation of a transporter can potentially alter these absorbtion, distribution, metabolism and elimination properties...... and thereby also the pharmacokinetic profile and bioavailability of drug compounds. P-glycoprotein (P-gp, ABCB1) is an efflux transporter which is present in most of the barriers of the body, including the small intestine, the blood-brain barrier, the liver, and the kidney. In all these tissues, P-gp may...... mediate efflux of drug compounds and may also be a potential site for drug-drug interactions. Consequently, there is a need to be able to predict the saturation and inhibition of P-gp and other transporters in vivo. For this purpose, Michaelis-Menten steady-state analysis has been applied to estimate...

  16. Iron colloids reduce the bioavailability of phosphorus to the green alga Raphidocelis subcapitata.

    Science.gov (United States)

    Baken, Stijn; Nawara, Sophie; Van Moorleghem, Christoff; Smolders, Erik

    2014-08-01

    Phosphorus (P) is a limiting nutrient in many aquatic systems. The bioavailability of P in natural waters strongly depends on its speciation. In this study, structural properties of iron colloids were determined and related to their effect on P sorption and P bioavailability. The freshwater green alga Raphidocelis subcapitata was exposed to media spiked with radiolabelled (33)PO4, and the uptake of (33)P was monitored for 1 h. The media contained various concentrations of synthetic iron colloids with a size between 10 kDa and 0.45 μm. The iron colloids were stabilised by natural organic matter. EXAFS spectroscopy showed that these colloids predominantly consisted of ferrihydrite with small amounts of organically complexed Fe. In colloid-free treatments, the P uptake flux by the algae obeyed Michaelis-Menten kinetics. In the presence of iron colloids at 9 or 90 μM Fe, corresponding to molar P:Fe ratios between 0.02 and 0.17, the truly dissolved P (<10 kDa) was between 4 and 60% of the total dissolved P (<0.45 μm). These colloids reduced the P uptake flux by R. subcapitata compared to colloid-free treatments at the same total dissolved P concentration. However, the P uptake flux from colloid containing solutions equalled that from colloid-free ones when expressed as truly dissolved P. This demonstrates that colloidal P did not contribute to the P uptake flux. It is concluded that, on the short term, phosphate adsorbed to ferrihydrite colloids is not available to the green alga R. subcapitata. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. The repair-fixation model: general aspects and the influence of radiation quality

    International Nuclear Information System (INIS)

    Kiefer, J.; Loebrich, M.

    1992-01-01

    To explain the shape of cell survival curves after radiation action it is assumed that initial lesions are transient in nature and subject to repair or fixation. Since the underlying processes are controlled by enzymes, Michaelis-Menten kinetics are assumed. No qualitative differences between repair and fixation are postulated, the only differences being the kinetic parameters. This model yields a mathematical expression which is formally equivalent to the ''lethal-potentially-lethal'' (LPL) model. It is demonstrated that both mammalian as well as microbial survival data can be fitted. The inclusion of linear energy transfer (LET) effects is shown to be possible and is discussed qualitatively. (author)

  18. Oxidation study of the synthetic sulfides molybdenite (MoS2) and covellite (CuS) by acidithiobacillus ferrooxidants using respirometric experiments

    International Nuclear Information System (INIS)

    Francisco Junior, Wilmo E.; Universidade Estadual Paulista; Bevilaqua, Denise; Garcia Junior, Oswaldo

    2009-01-01

    This paper analyses the oxidation of covellite and molybdenite by Acidithiobacillus ferrooxidans strain LR using respirometric experiments. The results showed that both sulfides were oxidized by A. ferrooxidans, however, the covellite oxidation was much higher than molybdenite. Regarding the kinetic oxidation, the findings revealed that just molybdenite oxidation followed the classical Michaelis-Menten kinetic. It is probably associated with the pathway which these sulfides react to chemistry-bacterial attack, what is influenced by its electronic structures. Besides, experiments conducted in the presence of Fe 3+ did not indicate alterations in molybdenite oxidation. Thus, ferric ions seem not to be essential to the sulfide oxidations. (author)

  19. Estudo da dissolução oxidativa microbiológica de uma complexa amostra mineral contendo pirita (FeS2, Pirrotita (Fe1-xS e Molibdenita (MoS2 Microbiological oxidative dissolution of a complex mineral sample containing pyrite (FeS2, pyrrotite (Fe1-xS and molybdenite (MoS2

    Directory of Open Access Journals (Sweden)

    Wilmo E. Francisco Jr

    2007-10-01

    Full Text Available This work aims to study the oxidation of a complex molybdenite mineral which contains pyrite and pyrrotite, by Acidithiobacillus ferrooxidans. This study was performed by respirometric essays and bioleaching in shake flasks. Respirometric essays yielded the kinetics of mineral oxidation. The findings showed that sulfide oxidation followed classical Michaelis-Menten kinetics. Bioleaching in shake flasks allowed evaluation of chemical and mineralogical changes resulting from sulfide oxidation. The results demonstrated that pyrrotite and pyrite were completely oxidized in A. ferrooxidans cultures whereas molybdenite was not consumed. These data indicated that molybdenite was the most recalcitrant sulfide in the sample.

  20. Microbiological oxidative dissolution of a complex mineral sample containing pyrite (FeS2), pyrrotite (Fe1-xS) and molybdenite (MoS2)

    International Nuclear Information System (INIS)

    Francisco Junior, Wilmo E.; Bevilaqua, Denise; Garcia Junior, Oswaldo

    2007-01-01

    This work aims to study the oxidation of a complex molybdenite mineral which contains pyrite and pyrrotite, by Acidithiobacillus ferroxidans. This study was performed by respirometric essays and bioleaching in shake flasks. Respirometric essays yielded the kinetics of mineral oxidation. The findings showed that sulfide oxidation followed classical Michaelis-Menten kinetics. Bioleaching in shake flasks allowed evaluation of chemical and mineralogical changes resulting from sulfide oxidation. The results demonstrated that pyrrotite and pyrite were completely oxidized in A. ferrooxidans cultures whereas molybdenite was not consumed. These data indicated that molybdenite was the most recalcitrant sulfide in the sample. (author)

  1. Microbiological oxidative dissolution of a complex mineral sample containing pyrite (FeS{sub 2}), pyrrotite (Fe{sub 1-x}S) and molybdenite (MoS{sub 2}); Estudo da dissolucao oxidativa microbiologica de uma complexa amostra mineral contendo pirita (FeS{sub 2}), Pirrotita (Fe{sub 1-x}S) e Molibdenita (MoS{sub 2})

    Energy Technology Data Exchange (ETDEWEB)

    Francisco Junior, Wilmo E.; Bevilaqua, Denise; Garcia Junior, Oswaldo [UNESP, Araraquara, SP (Brazil). Inst. de Quimica. Dept. de Bioquimica e Tecnologia Quimica]. E-mail: wilmojr@bol.com.br

    2007-09-15

    This work aims to study the oxidation of a complex molybdenite mineral which contains pyrite and pyrrotite, by Acidithiobacillus ferroxidans. This study was performed by respirometric essays and bioleaching in shake flasks. Respirometric essays yielded the kinetics of mineral oxidation. The findings showed that sulfide oxidation followed classical Michaelis-Menten kinetics. Bioleaching in shake flasks allowed evaluation of chemical and mineralogical changes resulting from sulfide oxidation. The results demonstrated that pyrrotite and pyrite were completely oxidized in A. ferrooxidans cultures whereas molybdenite was not consumed. These data indicated that molybdenite was the most recalcitrant sulfide in the sample. (author)

  2. Oxidation study of the synthetic sulfides molybdenite (MoS{sub 2}) and covellite (CuS) by acidithiobacillus ferrooxidants using respirometric experiments; Estudo da oxidacao dos sulfetos sinteticos molibdenita (MoS2) e covelita (CuS) por Acidithiobacillus ferrooxidans via respirometria celular

    Energy Technology Data Exchange (ETDEWEB)

    Francisco Junior, Wilmo E. [Universidade Federal de Rondonia (UFRO), Porto Velho, RO (Brazil). Dept. de Quimica; Universidade Estadual Paulista (UNESP), Araraquara, SP (Brazil). Inst. de Quimica. Dept. de Bioquimica e Tecnologia Quimica], e-mail: wilmojr@bol.com.br; Bevilaqua, Denise; Garcia Junior, Oswaldo [Universidade Estadual Paulista (UNESP), Araraquara, SP (Brazil). Inst. de Quimica. Dept. de Bioquimica e Tecnologia Quimica

    2009-07-01

    This paper analyses the oxidation of covellite and molybdenite by Acidithiobacillus ferrooxidans strain LR using respirometric experiments. The results showed that both sulfides were oxidized by A. ferrooxidans, however, the covellite oxidation was much higher than molybdenite. Regarding the kinetic oxidation, the findings revealed that just molybdenite oxidation followed the classical Michaelis-Menten kinetic. It is probably associated with the pathway which these sulfides react to chemistry-bacterial attack, what is influenced by its electronic structures. Besides, experiments conducted in the presence of Fe{sup 3+} did not indicate alterations in molybdenite oxidation. Thus, ferric ions seem not to be essential to the sulfide oxidations. (author)

  3. Estudo da oxidação dos sulfetos sintéticos molibdenita (MoS2 e covelita (CuS por Acidithiobacillus ferrooxidans via respirometria celular Oxidation study of the synthetic sulfides molybdenite (MoS2 and covellite (CuS by Acidithiobacillus ferrooxidans using respirometric experiments

    Directory of Open Access Journals (Sweden)

    Wilmo E. Francisco Junior

    2009-01-01

    Full Text Available This paper analyses the oxidation of covellite and molybdenite by Acidithiobacillus ferrooxidans strain LR using respirometric experiments. The results showed that both sulfides were oxidized by A. ferrooxidans, however, the covellite oxidation was much higher than molybdenite. Regarding the kinetic oxidation, the findings revealed that just molybdenite oxidation followed the classical Michaelis-Menten kinetic. It is probably associated with the pathway which these sulfides react to chemistry-bacterial attack, what is influenced by its electronic structures. Besides, experiments conducted in the presence of Fe3+ did not indicate alterations in molybdenite oxidation. Thus, ferric ions seem not to be essential to the sulfide oxidations.

  4. Global scale analysis and evaluation of an improved mechanistic representation of plant nitrogen and carbon dynamics in the Community Land Model (CLM)

    Science.gov (United States)

    Ghimire, B.; Riley, W. J.; Koven, C. D.; Randerson, J. T.; Mu, M.; Kattge, J.; Rogers, A.; Reich, P. B.

    2014-12-01

    In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However mechanistic representation of nitrogen uptake linked to root traits, and functional nitrogen allocation among different leaf enzymes involved in respiration and photosynthesis is currently lacking in Earth System models. The linkage between nitrogen availability and plant productivity is simplistically represented by potential photosynthesis rates, and is subsequently downregulated depending on nitrogen supply and other nitrogen consumers in the model (e.g., nitrification). This type of potential photosynthesis rate calculation is problematic for several reasons. Firstly, plants do not photosynthesize at potential rates and then downregulate. Secondly, there is considerable subjectivity on the meaning of potential photosynthesis rates. Thirdly, there exists lack of understanding on modeling these potential photosynthesis rates in a changing climate. In addition to model structural issues in representing photosynthesis rates, the role of plant roots in nutrient acquisition have been largely ignored in Earth System models. For example, in CLM4.5, nitrogen uptake is linked to leaf level processes (e.g., primarily productivity) rather than root scale process involved in nitrogen uptake. We present a new plant model for CLM with an improved mechanistic presentation of plant nitrogen uptake based on root scale Michaelis Menten kinetics, and stronger linkages between leaf nitrogen and plant productivity by inferring relationships observed in global databases of plant traits (including the TRY database and several individual studies). We also incorporate improved representation of plant nitrogen leaf allocation, especially in tropical regions where significant over-prediction of plant growth and productivity in CLM4.5 simulations exist. We evaluate our improved global model simulations using the International Land Model Benchmarking (ILAMB) framework. We conclude that

  5. pH modulates transport rates of manganese and cadmium in the green alga Chlamydomonas reinhardtii through non-competitive interactions: Implications for an algal BLM

    International Nuclear Information System (INIS)

    Francois, Laura; Fortin, Claude; Campbell, Peter G.C.

    2007-01-01

    The influence of pH on short-term uptake of manganese and cadmium by the green alga Chlamydomonas reinhardtii was studied to better understand the nature of proton interactions with metal membrane transporters. Manganese and cadmium internalization fluxes (J int ) were measured over a wide range of free metal ion concentrations from 1 x 10 -10 to 4 x 10 -4 M at several pH values (Mn: 5.0, 6.5 and 8.0; Cd: 5.0 and 6.5). For both metals, first-order biological internalization kinetics were observed but the maximum transport flux (J max ) decreased when pH decreased, in contradiction with the Biotic Ligand Model (BLM). This result suggested a non-competitive inhibition of metal uptake by the H + -ion. A Michaelis-Menten type inhibition model considering proton and calcium competition was tested. The metal biotic ligand stability constants and the stability constants for competitive binding of Ca 2+ and H + with the metal transporters were calculated: for manganese, K Mn = 10 4.20 and K Ca = 10 3.71 ; for cadmium, K Cd = 10 4.19 and K Ca = 10 4.76 ; for both metal transport systems, K H was not a significant parameter. Furthermore, metal uptake was not significantly influenced by the pH of the antecedent growth medium, suggesting that increases in metal fluxes as the pH is raised are caused by conformational changes of the surface transport proteins rather than by the synthesis of additional transport sites. Our results demonstrate that the BLM in its present state does not properly describe the true influence of pH on manganese and cadmium uptake by algae and that a non-competitive inhibition component must be integrated

  6. Understanding the sub-cellular dynamics of silicon transportation and synthesis in diatoms using population-level data and computational optimization.

    Directory of Open Access Journals (Sweden)

    Narjes Javaheri

    2014-06-01

    Full Text Available Controlled synthesis of silicon is a major challenge in nanotechnology and material science. Diatoms, the unicellular algae, are an inspiring example of silica biosynthesis, producing complex and delicate nano-structures. This happens in several cell compartments, including cytoplasm and silica deposition vesicle (SDV. Considering the low concentration of silicic acid in oceans, cells have developed silicon transporter proteins (SIT. Moreover, cells change the level of active SITs during one cell cycle, likely as a response to the level of external nutrients and internal deposition rates. Despite this topic being of fundamental interest, the intracellular dynamics of nutrients and cell regulation strategies remain poorly understood. One reason is the difficulties in measurements and manipulation of these mechanisms at such small scales, and even when possible, data often contain large errors. Therefore, using computational techniques seems inevitable. We have constructed a mathematical model for silicon dynamics in the diatom Thalassiosira pseudonana in four compartments: external environment, cytoplasm, SDV and deposited silica. The model builds on mass conservation and Michaelis-Menten kinetics as mass transport equations. In order to find the free parameters of the model from sparse, noisy experimental data, an optimization technique (global and local search, together with enzyme related penalty terms, has been applied. We have connected population-level data to individual-cell-level quantities including the effect of early division of non-synchronized cells. Our model is robust, proven by sensitivity and perturbation analysis, and predicts dynamics of intracellular nutrients and enzymes in different compartments. The model produces different uptake regimes, previously recognized as surge, externally-controlled and internally-controlled uptakes. Finally, we imposed a flux of SITs to the model and compared it with previous classical kinetics

  7. Intracellular accumulation of potent amiloride analogues by human neutrophils

    International Nuclear Information System (INIS)

    Simchowitz, L.; Woltersdorf, O.W. Jr.; Cragoe, E.J. Jr.

    1987-01-01

    The mechanism of uptake of a series of amiloride derivatives by human neutrophils was investigated using [ 14 C]amiloride and the 14 C-labeled 5-(1-hexahydroazepinyl)-6-bromo analogue (BrMM) which is approximately 500-fold more potent than the parent compound at inhibiting Na+/H+ exchange. At an external concentration of 2 microM, the influx of BrMM at 37 degrees C was rapid, reaching a steady state by approximately 20 min. The rate of BrMM uptake (approximately 25 mumol/liter.min) was approximately 90-fold faster than for the same concentration of amiloride, a finding which correlates with differences in lipid partitioning of the two compounds. Uptake was unrelated to specific binding to Na+/H+ exchange transport sites: influx of either drug was nonsaturable whereas amiloride- and BrMM-mediated inhibition of Na+/H+ countertransport obeyed Michaelis-Menten kinetics with apparent Ki values of approximately 75 and approximately 0.2 microM. Entry occurred exclusively via the neutral (uncharged) forms (pK'a 8.40-8.55). Influx was markedly pH-dependent: it was enhanced by extracellular alkalinization and reduced by acidification. Influx was, however, insensitive to large changes in membrane voltage, thereby implying the protonated (charged) species to be impermeant. About 75% of the total intracellular pool of amiloride, but only approximately 25% of BrMM, is contained within the lysosomes, an expected consequence of the partitioning and subsequent trapping of a weak base within this strongly acidic subcellular compartment. With BrMM, there was a relative approximately 60-fold enrichment in the internal/external water concentration ratio of the drug; the value for amiloride was much less, approximately 4. This disparity is consistent with substantial binding of BrMM to internal constituents, presumably to proteins and/or nucleic acids

  8. Representing leaf and root physiological traits in CLM improves global carbon and nitrogen cycling predictions

    Science.gov (United States)

    Ghimire, Bardan; Riley, William J.; Koven, Charles D.; Mu, Mingquan; Randerson, James T.

    2016-06-01

    In many ecosystems, nitrogen is the most limiting nutrient for plant growth and productivity. However, current Earth System Models (ESMs) do not mechanistically represent functional nitrogen allocation for photosynthesis or the linkage between nitrogen uptake and root traits. The current version of CLM (4.5) links nitrogen availability and plant productivity via (1) an instantaneous downregulation of potential photosynthesis rates based on soil mineral nitrogen availability, and (2) apportionment of soil nitrogen between plants and competing nitrogen consumers assumed to be proportional to their relative N demands. However, plants do not photosynthesize at potential rates and then downregulate; instead photosynthesis rates are governed by nitrogen that has been allocated to the physiological processes underpinning photosynthesis. Furthermore, the role of plant roots in nutrient acquisition has also been largely ignored in ESMs. We therefore present a new plant nitrogen model for CLM4.5 with (1) improved representations of linkages between leaf nitrogen and plant productivity based on observed relationships in a global plant trait database and (2) plant nitrogen uptake based on root-scale Michaelis-Menten uptake kinetics. Our model improvements led to a global bias reduction in GPP, LAI, and biomass of 70%, 11%, and 49%, respectively. Furthermore, water use efficiency predictions were improved conceptually, qualitatively, and in magnitude. The new model's GPP responses to nitrogen deposition, CO2 fertilization, and climate also differed from the baseline model. The mechanistic representation of leaf-level nitrogen allocation and a theoretically consistent treatment of competition with belowground consumers led to overall improvements in global carbon cycling predictions.

  9. Competition between roots and microorganisms for nitrogen: mechanisms and ecological relevance.

    Science.gov (United States)

    Kuzyakov, Yakov; Xu, Xingliang

    2013-05-01

    Demand of all living organisms on the same nutrients forms the basis for interspecific competition between plants and microorganisms in soils. This competition is especially strong in the rhizosphere. To evaluate competitive and mutualistic interactions between plants and microorganisms and to analyse ecological consequences of these interactions, we analysed 424 data pairs from 41 (15)N-labelling studies that investigated (15)N redistribution between roots and microorganisms. Calculated Michaelis-Menten kinetics based on K(m) (Michaelis constant) and V(max) (maximum uptake capacity) values from 77 studies on the uptake of nitrate, ammonia, and amino acids by roots and microorganisms clearly showed that, shortly after nitrogen (N) mobilization from soil organic matter and litter, microorganisms take up most N. Lower K(m) values of microorganisms suggest that they are especially efficient at low N concentrations, but can also acquire more N at higher N concentrations (V(max)) compared with roots. Because of the unidirectional flow of nutrients from soil to roots, plants are the winners for N acquisition in the long run. Therefore, despite strong competition between roots and microorganisms for N, a temporal niche differentiation reflecting their generation times leads to mutualistic relationships in the rhizosphere. This temporal niche differentiation is highly relevant ecologically because it: protects ecosystems from N losses by leaching during periods of slow or no root uptake; continuously provides roots with available N according to plant demand; and contributes to the evolutionary development of mutualistic interactions between roots and microorganisms. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

  10. Kinetic Typography

    DEFF Research Database (Denmark)

    van Leeuwen, Theo; Djonov, Emilia

    2014-01-01

    After discussing broad cultural drivers behind the development of kinetic typography, the chapter outlines an approach to analysing kinetic typography which is based on Halliday's theory of transitivity, as applied by Kress and Van Leeuwen to visual images.......After discussing broad cultural drivers behind the development of kinetic typography, the chapter outlines an approach to analysing kinetic typography which is based on Halliday's theory of transitivity, as applied by Kress and Van Leeuwen to visual images....

  11. Solvent 1H/2H isotopic effects in the reaction of the L-Tyrosine oxidation catalyzed by Tyrosinase

    International Nuclear Information System (INIS)

    Kozlowska, M.; Kanska, M.

    2006-01-01

    Tyrosinase is well known catalyst in the oxidation of L-Tyrosine to L-DOPA and following oxidation of L-DOPA to dopachinone. The aim of communication is to present the results of studies on the solvent isotopic effects (SIE) in the above reactions for the 1 H/ 2 H in the 3',5' and 2',6' substituted tyrosine. Obtained dependence of the reaction rate on the substrate concentration were applied for optimization of the kinetic parameters, k cat and k cat /K m , in the Michaelis-Menten equation. As a result - better understanding of the L-DOPA creation can be achieved

  12. Metabolomics on integrated circuit

    OpenAIRE

    Cheah, Boon Chong; MacDonald, Alasdair I.; Barrett, Michael P.; Cumming, David R.S.

    2017-01-01

    We have demonstrated a chip-based diagnostics tool for the quantification of metabolites, using specific enzymes, to study enzyme kinetics and calculate the Michaelis-Menten constant. An array of 256×256 ion-sensitive field effect transistors (ISFETs) fabricated in a complementary metal oxide semiconductor (CMOS) process is used for this prototype. We have used hexokinase enzyme reaction on the ISFET CMOS chip with glucose concentration in the physiological range of 0.05 mM – 231 mM and succe...

  13. Modelling the Effects of Ageing Time of Starch on the Enzymatic Activity of Three Amylolytic Enzymes

    Science.gov (United States)

    Guerra, Nelson P.; Pastrana Castro, Lorenzo

    2012-01-01

    The effect of increasing ageing time (t) of starch on the activity of three amylolytic enzymes (Termamyl, San Super, and BAN) was investigated. Although all the enzymatic reactions follow michaelian kinetics, v max decreased significantly (P enzymes and the release of the reaction products to the medium. A similar effect was observed when the enzymatic reactions were carried out with unaged starches supplemented with different concentrations of gelatine [G]. The inhibition in the amylolytic activities was best mathematically described by using three modified forms of the Michaelis-Menten model, which included a term to consider, respectively, the linear, exponential, and hyperbolic inhibitory effects of t and [G]. PMID:22666116

  14. Uptake of cadmium from hydroponic solutions by willows (Salix spp ...

    African Journals Online (AJOL)

    DR. NJ TONUKARI

    2011-11-16

    Nov 16, 2011 ... which indicated that cadmium uptake across the plasma membrane was ... to cadmium pollution in water-soil-plant systems because .... plants were separated into roots and shoots, blotted dry with paper tissue .... Analysis of the kinetic constants for cadmium uptake ..... proteins (Welch and Norvell, 1999).

  15. Uptake and depuration of gold nanoparticles in Daphnia magna

    DEFF Research Database (Denmark)

    Skjolding, Lars Michael; Kern, Kristina; Hjorth, Rune

    2014-01-01

    This study presents a series of short-term studies (total duration 48 h) of uptake and depuration of engineered nanoparticles (ENP) in neonate Daphnia magna. Gold nanoparticles (Au NP) were used to study the influence of size, stabilizing agent and feeding on uptake and depuration kinetics...

  16. Uptake kinetics of the somatostatin receptor ligand [86Y]DOTA-dPhe1-Tyr3-octreotide ([86Y]SMT487) using positron emission tomography in non-human primates and calculation of radiation doses of the 90Y-labelled analogue

    International Nuclear Information System (INIS)

    Roesch, F.; Brockmann, J.; Koehle, M.

    1999-01-01

    [ 90 Y]DOTA-dPhe 1 -Tyr 3 -octreotide ([ 90 Y]-SMT487) has been suggested as a promising radiotherapeutic agent for somatostatin receptor-expressing tumours. In order to quantify the in vivo parameters of this compound and the radiation doses delivered to healthy organs, the analogue [ 86 Y]DOTA-dPhe 1 -Tyr 3 -octreotide was synthesised and its uptake measured in baboons using positron emission tomography (PET). [ 86 Y]DOTA-dPhe 1 -Tyr 3 -octreotide was administered at two different peptide concentrations, namely 2 and 100 μg peptide per m 2 body surface. The latter concentration corresponded to a radiotherapeutic dose. In a third protocol [ 86 Y]DOTA-dPhe 1 -Tyr 3 -octreotide was injected in conjunction with a simultaneous infusion of an amino acid solution that was high in l-lysine in order to lower the renal uptake of radioyttrium. Quantitative whole-body PET scans were recorded to measure the uptake kinetics for kidneys, liver, lung and bone. The individual absolute uptake kinetics were used to calculate the radiation doses for [ 90 Y]DOTA-dPhe 1 -Tyr 3 -octreotide according to the MIRD recommendations extrapolated to a 70-kg human. The highest radiation dose was received by the kidneys, with 2.1-3.3 mGy per MBq [ 90 Y]DOTA-dPhe 1 -Tyr 3 -octreotide injected. For the 100 μg/m 2 SMT487 protocol with amino acid co-infusion this dose was about 20%-40% lower than for the other two treatment protocols. The liver and the red bone marrow received doses ranging from 0.32 to 0.53 mGy and 0.03 to 0.07 mGy per MBq [ 90 Y]DOTA-dPhe 1 -Tyr 3 -octreotide, respectively. The average effective dose equivalent amounted to 0.23-0.32 mSv/MBq. The comparatively low estimated radiation doses to normal organs support the initiation of clinical phase I trials with [ 90 Y]DOTA-dPhe 1 -Tyr 3 -octreotide in patients with somatostatin receptor-expressing tumours. (orig.)

  17. Uptake kinetics of the somatostatin receptor ligand [{sup 86}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide ([{sup 86}Y]SMT487) using positron emission tomography in non-human primates and calculation of radiation doses of the {sup 90}Y-labelled analogue

    Energy Technology Data Exchange (ETDEWEB)

    Roesch, F.; Brockmann, J. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Nuklearchemie; Herzog, H.; Muehlensiepen, H.; Mueller-Gaertner, H.W. [Forschungszentrum Juelich GmbH (Germany). Inst. fuer Medizin; Stolz, B.; Marbach, P. [Novartis Pharma AG, Basel (Switzerland); Koehle, M. [Klinikum der Freien Universitaet Berlin (Germany)

    1999-04-29

    [{sup 90}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide ([{sup 90}Y]-SMT487) has been suggested as a promising radiotherapeutic agent for somatostatin receptor-expressing tumours. In order to quantify the in vivo parameters of this compound and the radiation doses delivered to healthy organs, the analogue [{sup 86}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide was synthesised and its uptake measured in baboons using positron emission tomography (PET). [{sup 86}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide was administered at two different peptide concentrations, namely 2 and 100 {mu}g peptide per m{sup 2} body surface. The latter concentration corresponded to a radiotherapeutic dose. In a third protocol [{sup 86}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide was injected in conjunction with a simultaneous infusion of an amino acid solution that was high in l-lysine in order to lower the renal uptake of radioyttrium. Quantitative whole-body PET scans were recorded to measure the uptake kinetics for kidneys, liver, lung and bone. The individual absolute uptake kinetics were used to calculate the radiation doses for [{sup 90}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide according to the MIRD recommendations extrapolated to a 70-kg human. The highest radiation dose was received by the kidneys, with 2.1-3.3 mGy per MBq [{sup 90}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide injected. For the 100 {mu}g/m{sup 2} SMT487 protocol with amino acid co-infusion this dose was about 20%-40% lower than for the other two treatment protocols. The liver and the red bone marrow received doses ranging from 0.32 to 0.53 mGy and 0.03 to 0.07 mGy per MBq [{sup 90}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide, respectively. The average effective dose equivalent amounted to 0.23-0.32 mSv/MBq. The comparatively low estimated radiation doses to normal organs support the initiation of clinical phase I trials with [{sup 90}Y]DOTA-dPhe{sup 1}-Tyr{sup 3}-octreotide in patients with somatostatin receptor-expressing tumours. (orig

  18. Biodegradation of BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) composites present in the petrochemical effluents industries; Biodegradacao dos compostos BTX (Benzeno, Tolueno e Xilenos) presentes em efluentes petroquimicos

    Energy Technology Data Exchange (ETDEWEB)

    Minatti, Gheise; Mello, Josiane M.M. de; Souza, Selene M.A. Guelli Ulson de; Ulson de, Antonio Augusto [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil)

    2008-07-01

    The compounds BTX inside of the petrochemical effluent have presented a high potential of pollution, representing a serious risk to the environment and to the human. The great improvements in the field of biological treatment of liquid effluent were reached through the process using biofilm capable of degrading toxic compounds. The objective of this paper is to determine the degradation kinetics of BTX using biofilm. The experimental data were compared with two kinetic models, kinetic of first order and model of Michaelis-Menten. The kinetic parameters of BTX compounds were experimentally obtained in a bioreactor in batch with biomass immobilized in activated-carbon, being fed daily with solution of nutrients and BTX. For the kinetic models studied in this paper, the best performance was achieved with the model of Michaelis-Menten showing a good correlation coefficient for the three compounds. The biomass amount in these bioreactors was 49.18, 28.35 and 5.15 mg of SSV per gram of support for the toluene, benzene and o-xylene, respectively. The experimental tests showed that the biomass inside of bioreactor is capable to degrade all compounds in a time of approximately 300 minutes. (author)

  19. Stopped-Flow Spectrophotometric Study of the Kinetics and Mechanism of CO2 Uptake by cis-[Cr(C2O4(BaraNH2(OH22]+ Cation and the Acid-Catalyzed Decomposition of cis-[Cr(C2O4(BaraNH2OCO2]− Anion in Aqueous Solution

    Directory of Open Access Journals (Sweden)

    Lech Chmurzyński

    2011-09-01

    Full Text Available The kinetics of CO2 uptake by the cis-[Cr(C2O4(BaraNH2(OH22]+ complex cation and the acid hydrolysis of the cis-[Cr(C2O4(BaraNH2OCO2]− complex anion (where BaraNH2 denotes methyl 3-amino-2,3-dideoxy-b-D-arabino-hexopyranoside were studied using the stopped-flow technique. The reactions under study were investigated in aqueous solution in the 288–308 K temperature range. In the case of the reaction between CO2 and cis-[Cr(C2O4(BaraNH2(OH22]+ cation variable pH values (6.82–8.91 and the constant ionic strength of solution (H+, Na+, ClO4− = 1.0 were used. Carbon dioxide was generated by the reaction between sodium pyruvate and hydrogen peroxide. The acid hydrolysis of cis-[Cr(C2O4(BaraNH2OCO2]− was investigated for varying concentrations of H+ ions (0.01–2.7 M. The obtained results enabled the determination of the number of steps of the studied reactions. Based on the kinetic equations, rate constants were determined for each step. Finally, mechanisms for both reactions were proposed and discussed. Based on the obtained results it was concluded that the carboxylation (CO2 uptake reactions of cis-[Cr(C2O4(BaraNH2(OH22]+ and the decarboxylation (acid hydrolysis of the cis-[Cr(C2O4(BaraNH2OCO2]− are the opposite of each other.

  20. Understanding transporter specificity and the discrete appearance of channel-like gating domains in transporters

    Directory of Open Access Journals (Sweden)

    GEORGE eDIALLINAS

    2014-09-01

    Full Text Available Transporters are ubiquitous proteins mediating the translocation of solutes across cell membranes, a biological process involved in nutrition, signaling, neurotransmission, cell communication and drug uptake or efflux. Similarly to enzymes, most transporters have a single substrate binding-site and thus their activity follows Michaelis-Menten kinetics. Substrate binding elicits a series of structural changes, which produce a transporter conformer open towards the side opposite to the one from where the substrate was originally bound. This mechanism, involving alternate outward- and inward-facing transporter conformers, has gained significant support from structural, genetic, biochemical and biophysical approaches. Most transporters are specific for a given substrate or a group of substrates with similar chemical structure, but substrate specificity and/or affinity can vary dramatically, even among members of a transporter family that show high overall amino acid sequence and structural similarity. The current view is that transporter substrate affinity or specificity is determined by a small number of interactions a given solute can make within a specific binding site. However, genetic, biochemical and in silico modeling studies with the purine transporter UapA of the filamentous ascomycete Aspergillus nidulans have challenged this dogma. This review highlights results leading to a novel concept, stating that substrate specificity, but also transport kinetics and transporter turnover, are determined by subtle intramolecular interactions between a major substrate binding site and independent outward- or cytoplasmically-facing gating domains, analogous to those present in channels. This concept is supported by recent structural evidence from several, phylogenetically and functionally distinct transporter families. The significance of this concept is discussed in relationship to the role and potential exploitation of transporters in drug action.

  1. Modeling networks of coupled enzymatic reactions using the total quasi-steady state approximation.

    Directory of Open Access Journals (Sweden)

    Andrea Ciliberto

    2007-03-01

    Full Text Available In metabolic networks, metabolites are usually present in great excess over the enzymes that catalyze their interconversion, and describing the rates of these reactions by using the Michaelis-Menten rate law is perfectly valid. This rate law assumes that the concentration of enzyme-substrate complex (C is much less than the free substrate concentration (S0. However, in protein interaction networks, the enzymes and substrates are all proteins in comparable concentrations, and neglecting C with respect to S0 is not valid. Borghans, DeBoer, and Segel developed an alternative description of enzyme kinetics that is valid when C is comparable to S0. We extend this description, which Borghans et al. call the total quasi-steady state approximation, to networks of coupled enzymatic reactions. First, we analyze an isolated Goldbeter-Koshland switch when enzymes and substrates are present in comparable concentrations. Then, on the basis of a real example of the molecular network governing cell cycle progression, we couple two and three Goldbeter-Koshland switches together to study the effects of feedback in networks of protein kinases and phosphatases. Our analysis shows that the total quasi-steady state approximation provides an excellent kinetic formalism for protein interaction networks, because (1 it unveils the modular structure of the enzymatic reactions, (2 it suggests a simple algorithm to formulate correct kinetic equations, and (3 contrary to classical Michaelis-Menten kinetics, it succeeds in faithfully reproducing the dynamics of the network both qualitatively and quantitatively.

  2. Application of nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, UV-Visible spectroscopy and kinetic modeling for elucidation of adsorption chemistry in uptake of tetracycline by zeolite beta.

    Science.gov (United States)

    Kang, Jin; Liu, Huijuan; Zheng, Yu-Ming; Qu, Jiuhui; Chen, J Paul

    2011-02-01

    Extensive usage of tetracycline has resulted in its contamination in surface water and groundwater. The adsorption of tetracycline on zeolite beta was systematically investigated for the decontamination of the antibiotic polluted water in this study. Ninety percent of uptake by the zeolite beta occured in 0.25h, and the adsorption equilibrium was obtained within 3h, which was well described by an intraparticle diffusion model. The adsorption generally increased when pH was increased from 4.0 to 5.0, and then decreased significantly as the pH was further increased, which was caused by the pH-dependent speciation of tetracycline and surface charge of zeolite beta. Both Freundlich and Langmuir equations well described the adsorption isotherm. A thermodynamic analysis showed that the sorption process was spontaneous and endothermic. Aluminum atoms in the zeolite played a crucial role in the uptake; the adsorption increased with the increasing aluminum content in zeolite. The UV-Visible spectroscopy study showed that the spectra of tetracycline changed upon the interaction with zeolite beta, which could be ascribed to the formation of complexes of tetracycline and aluminum atoms in the zeolite surface. Nuclear magnetic resonance spectroscopy study further confirmed the participation of Al in the tetracycline adsorption. Fourier transform infrared spectroscopy studies showed that the amino functional groups in tetracycline were involved in the complexation with the zeolite surface. Copyright © 2010 Elsevier Inc. All rights reserved.

  3. Physical kinetics

    International Nuclear Information System (INIS)

    Lifschitz, E.M.; Pitajewski, L.P.

    1983-01-01

    The textbook covers the subject under the following headings: kinetic gas theory, diffusion approximation, collisionless plasma, collisions within the plasma, plasma in the magnetic field, theory of instabilities, dielectrics, quantum fluids, metals, diagram technique for nonequilibrium systems, superconductors, and kinetics of phase transformations

  4. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... for a thyroid scan is 30 minutes or less. Thyroid Uptake You will be given radioactive iodine ( ... for each thyroid uptake is five minutes or less. top of page What will I experience during ...

  5. Thyroid Scan and Uptake

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    Full Text Available ... uptake measurements are obtained at different times. For example, you may have uptake measurements at four to ... medicine procedures can be time consuming. It can take several hours to days for the radiotracer to ...

  6. Thyroid Scan and Uptake

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    Full Text Available ... Scan and Uptake Thyroid scan and uptake uses small amounts of radioactive materials called radiotracers, a special ... is a branch of medical imaging that uses small amounts of radioactive material to diagnose and determine ...

  7. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... radioactive iodine uptake test (RAIU) is also known as a thyroid uptake. It is a measurement of ... potential to identify disease in its earliest stages as well as a patient’s immediate response to therapeutic ...

  8. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... known as a thyroid uptake. It is a measurement of thyroid function, but does not involve imaging. ... eating can affect the accuracy of the uptake measurement. Jewelry and other metallic accessories should be left ...

  9. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... Uptake? A thyroid scan is a type of nuclear medicine imaging. The radioactive iodine uptake test (RAIU) ... of thyroid function, but does not involve imaging. Nuclear medicine is a branch of medical imaging that ...

  10. Decreased cisplatin uptake by resistant L1210 leukemia cells

    International Nuclear Information System (INIS)

    Hromas, R.A.; North, J.A.; Burns, C.P.

    1987-01-01

    Cisplatin resistance remains poorly understood compared to other forms of anti-neoplastic drug resistance. In this report radiolabelled cisplatin and rapid separation techniques were used to compare drug uptake by L1210 leukemia cells that are sensitive (K25) or resistant (SCR9) to cisplatin. Uptake of cisplatin by both cell lines was linear without saturation kinetics up to 100 μM. The resistant ZCR9 cells had 36-60% reduced drug uptake as compared to its sensitive parent line, K25. In contrast, there was no difference in the rate of efflux. We conclude that a decreased rate of uptake is one possible mechanism of cellular cisplatin resistance. (Author)

  11. Heparin kinetics

    International Nuclear Information System (INIS)

    Swart, C.A.M. de.

    1983-01-01

    The author has studied the kinetics of heparin and heparin fractions after intravenous administration in humans and in this thesis the results of this study are reported. Basic knowledge about the physico-chemical properties of heparin and its interactions with proteins resulting in anticoagulant and lipolytic effects are discussed in a review (chapter II), which also comprises some clinical aspects of heparin therapy. In chapter III the kinetics of the anticoagulant effect are described after intravenous administration of five commercial heparin preparations. A mathematical model is presented that fits best to these kinetics. The kinetics of the anticoagulant and lipolytic effects after intravenous injection of various 35 S-radiolabelled heparin fractions and their relationship with the disappearance of the radiolabel are described in chapter IV. Chapter V gives a description of the kinetics of two radiolabels after injection of in vitro formed complexes consisting of purified, 125 I-radiolabelled antithrombin III and various 35 S-radiolabelled heparin fractions. (Auth.)

  12. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... for a thyroid scan is 30 minutes or less. Thyroid Uptake You will be given radioactive iodine (I-123 or I-131) in liquid or capsule form to swallow. The thyroid uptake will begin several hours to 24 hours later. Often, two separate uptake ...

  13. Experimental study on Ra2+ uptake by barite (BaSO{sub 4}). Kinetics of solid solution formation via BaSO{sub 4} dissolution and Ra{sub x}Ba{sub 1-x}SO{sub 4} (re) precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Bosbach, Dirk; Boettle, Melanie; Metz, Volker (Karlsruher Inst. fuer Technologie, Inst fuer Nukleare Entsorgung (INE), Karlsruhe (Germany))

    2010-03-15

    226Ra2+ and 133Ba2+ uptake by barite in aqueous solution is studied on the basis of batch type experiments with two different barite powders with different specific surface area (0.5 m2/g and 3.2 m2/g, respectively). The uptake of 226Ra2+ and 133Ba2+ is not only limited to adsorption reactions but proceeds significantly into the bulk of the barite crystals. 133Ba2+ uptake kinetics is affected by various parameters, such as amount of sample, specific surface area, sample type and solution composition. In the case of 133Ba2+, complete isotopic equilibration of the 133Ba2+ spiked solution with the barite powder occurs within 50 to 600 days. This information is derived by monitoring the aqueous 133Ba2+ concentration combined with simple mass balance calculations. In the case of 226Ra2+ a Ra{sub x}Ba{sub 1-x}SO{sub 4} solid solution forms and the uptake rate drops significantly within 400 days. The observed 226Ra2+ concentration in solution is controlled by the solubility of a Ra{sub x}Ba{sub 1-x}SO{sub 4} solid solution and several orders of magnitude below the Ra2+ solubility with respect to a pure RaSO{sub 4}(s) end member. It cannot be demonstrated unambiguously that a zero exchange rate and therefore thermodynamic equilibrium has been established within the observation period. The observed concentrations may be interpreted either as (1) a partial equilibration of 20 to 50% of the barite crystals with 226Ra2+ or (2) as complete equilibration of a Ra{sub 0.000128}Ba{sub 0.999872}SO{sub 4} solid solution with 226Ra2+ with no pure barite left. In both cases it is concluded that equilibration between aqueous Ra2+ and barite involves the replacement of a substantial fraction of the initial barite and proceeds significantly beyond pure surface adsorption processes

  14. Platinum uptake from chloride solutions using biosorbents

    Directory of Open Access Journals (Sweden)

    Mehmet Hakan Morcali

    2013-04-01

    Full Text Available Present work investigates platinum uptake from synthetically prepared, dilute platinum-bearing solutions using biomass residues, i.e. pistachio nut shell and rice husk, which are abundant in Turkey, and provides a comparison between these two biosorbents. Effects of the different uptake parameters, sorbent dosage, contact time, temperature and pH of solution on platinum uptake (% were studied in detail on a batch sorption. Before the pistachio nut shell was activated, platinum uptake (% was poor compared to the rice husk. However, after the pistachio nut shell was activated at 1000 °C under an argon atmosphere, the platinum uptake (% increased two-fold. The pistachio nut shell (original and activated and rice husk were shown to be better than commercially available activated carbon in terms of adsorption capacity. These two sorbents have also been characterized by FTIR and SEM. Adsorption equilibrium data best complied with the Langmuir isotherm model. Maximum adsorption capacities, Qmax, at 25 °C were found to be 38.31 and 42.02 mg.g- 1for the activated pistachio nut shell and rice husk, respectively. Thermodynamic calculations using the measured ∆H°, ∆S° and ∆G° values indicate that the uptake process was spontaneous and endothermic. The experimental data were shown to be fit the pseudo-second-order kinetic model.

  15. Kinetic Interface

    DEFF Research Database (Denmark)

    2009-01-01

    A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises.......A kinetic interface for orientation detection in a video training system is disclosed. The interface includes a balance platform instrumented with inertial motion sensors. The interface engages a participant's sense of balance in training exercises....

  16. Effect of membranes on oxygen transfer rate and consumption within a newly developed three-compartment bioartificial liver device: Advanced experimental and theoretical studies.

    Science.gov (United States)

    Hilal-Alnaqbi, Ali; Mourad, Abdel-Hamid I; Yousef, Basem F

    2014-01-01

    A mathematical model is developed to predict oxygen transfer in the fiber-in-fiber (FIF) bioartificial liver device. The model parameters are taken from the constructed and tested FIF modules. We extended the Krogh cylinder model by including one more zone for oxygen transfer. Cellular oxygen uptake was based on Michaelis-Menten kinetics. The effect of varying a number of important model parameters is investigated, including (1) oxygen partial pressure at the inlet, (2) the hydraulic permeability of compartment B (cell region), (3) the hydraulic permeability of the inner membrane, and (4) the oxygen diffusivity of the outer membrane. The mathematical model is validated by comparing its output against the experimentally acquired values of an oxygen transfer rate and the hydrostatic pressure drop. Three governing simultaneous linear differential equations are derived to predict and validate the experimental measurements, e.g., the flow rate and the hydrostatic pressure drop. The model output simulated the experimental measurements to a high degree of accuracy. The model predictions show that the cells in the annulus can be oxygenated well even at high cell density or at a low level of gas phase PG if the value of the oxygen diffusion coefficient Dm is 16 × 10(-5) . The mathematical model also shows that the performance of the FIF improves by increasing the permeability of polypropylene membrane (inner fiber). Moreover, the model predicted that 60% of plasma has access to the cells in the annulus within the first 10% of the FIF bioreactor axial length for a specific polypropylene membrane permeability and can reach 95% within the first 30% of its axial length. © 2013 International Union of Biochemistry and Molecular Biology, Inc.

  17. Fock space, symbolic algebra, and analytical solutions for small stochastic systems.

    Science.gov (United States)

    Santos, Fernando A N; Gadêlha, Hermes; Gaffney, Eamonn A

    2015-12-01

    Randomness is ubiquitous in nature. From single-molecule biochemical reactions to macroscale biological systems, stochasticity permeates individual interactions and often regulates emergent properties of the system. While such systems are regularly studied from a modeling viewpoint using stochastic simulation algorithms, numerous potential analytical tools can be inherited from statistical and quantum physics, replacing randomness due to quantum fluctuations with low-copy-number stochasticity. Nevertheless, classical studies remained limited to the abstract level, demonstrating a more general applicability and equivalence between systems in physics and biology rather than exploiting the physics tools to study biological systems. Here the Fock space representation, used in quantum mechanics, is combined with the symbolic algebra of creation and annihilation operators to consider explicit solutions for the chemical master equations describing small, well-mixed, biochemical, or biological systems. This is illustrated with an exact solution for a Michaelis-Menten single enzyme interacting with limited substrate, including a consideration of very short time scales, which emphasizes when stiffness is present even for small copy numbers. Furthermore, we present a general matrix representation for Michaelis-Menten kinetics with an arbitrary number of enzymes and substrates that, following diagonalization, leads to the solution of this ubiquitous, nonlinear enzyme kinetics problem. For this, a flexible symbolic maple code is provided, demonstrating the prospective advantages of this framework compared to stochastic simulation algorithms. This further highlights the possibilities for analytically based studies of stochastic systems in biology and chemistry using tools from theoretical quantum physics.

  18. Rethinking fundamentals of enzyme action.

    Science.gov (United States)

    Northrop, D B

    1999-01-01

    Despite certain limitations, investigators continue to gainfully employ concepts rooted in steady-state kinetics in efforts to draw mechanistically relevant inferences about enzyme catalysis. By reconsidering steady-state enzyme kinetic behavior, this review develops ideas that allow one to arrive at the following new definitions: (a) V/K, the ratio of the maximal initial velocity divided by the Michaelis-Menten constant, is the apparent rate constant for the capture of substrate into enzyme complexes that are destined to yield product(s) at some later point in time; (b) the maximal velocity V is the apparent rate constant for the release of substrate from captured complexes in the form of free product(s); and (c) the Michaelis-Menten constant K is the ratio of the apparent rate constants for release and capture. The physiologic significance of V/K is also explored to illuminate aspects of antibiotic resistance, the concept of "perfection" in enzyme catalysis, and catalytic proficiency. The conceptual basis of congruent thermodynamic cycles is also considered in an attempt to achieve an unambiguous way for comparing an enzyme-catalyzed reaction with its uncatalyzed reference reaction. Such efforts promise a deeper understanding of the origins of catalytic power, as it relates to stabilization of the reactant ground state, stabilization of the transition state, and reciprocal stabilizations of ground and transition states.

  19. Elimination kinetic model for organic chemicals in earthworms.

    NARCIS (Netherlands)

    Dimitrova, N.; Dimitrov, S.; Georgieva, D.; van Gestel, C.A.M.; Hankard, P.; Spurgeon, D.J.; Li, H.; Mekenyan, O.

    2010-01-01

    Mechanistic understanding of bioaccumulation in different organisms and environments should take into account the influence of organism and chemical depending factors on the uptake and elimination kinetics of chemicals. Lipophilicity, metabolism, sorption (bioavailability) and biodegradation of

  20. Thyroid uptake test

    International Nuclear Information System (INIS)

    Ganatra, R.D.

    1992-01-01

    The uptake of radioiodine by the thyroid gland is altered by the iodine content of diet or drugs. American diet has a high iodine content because each slice of the white bread contains nearly 150μg of iodine due to the bleaching process employed in the production of the bread. This carrier content of iodine reduces the uptake so much, that the normal American uptakes are usually three to four times lower than the uptakes in the developing countries. The other drawback of the thyroid uptake test is that it is affected by the iodine containing drugs. Anti-diarrhoea medications are quire common in the developing countries and many of them contain iodine moiety. Without a reliable drug history, a low thyroid uptake value may lead to a misleading conclusion

  1. Kinetics and

    Directory of Open Access Journals (Sweden)

    Mojtaba Ahmadi

    2016-11-01

    Full Text Available The aqueous degradation of Reactive Yellow 84 (RY84 by potassium peroxydisulfate (K2S2O8 has been studied in laboratory scale experiments. The effect of the initial concentrations of potassium peroxydisulfate and RY84, pH and temperature on RY84 degradation were also examined. Experimental data were analyzed using first and second-order kinetics. The degradation kinetics of RY84 of the potassium peroxydisulfate process followed the second-order reaction kinetics. These rate constants have an extreme values similar to of 9.493 mM−1min−1 at a peroxydisulfate dose of 4 mmol/L. Thermodynamic parameters such as activation (Ea and Gibbs free energy (ΔG° were also evaluated. The negative value of ΔGo and Ea shows the spontaneous reaction natural conditions and exothermic nature.

  2. Granulocyte kinetics

    International Nuclear Information System (INIS)

    Peters, A.M.; Lavender, J.P.; Saverymuttu, S.H.

    1985-01-01

    By using density gradient materials enriched with autologous plasma, the authors have been able to isolate granulocutes from other cellular elements and label them with In-111 without separation from a plasma environment. The kinetic behavior of these cells suggests that phenomena attributed to granulocyte activation are greatly reduced by this labeling. Here, they review their study of granulocyte kinetics in health and disease in hope of quantifying sites of margination and identifying principal sites of destruction. The three principle headings of the paper are distribution, life-span, and destruction

  3. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available Toggle navigation Test/Treatment Patient Type Screening/Wellness Disease/Condition Safety En Español More Info Images/Videos About Us News Physician ... of nuclear medicine imaging. The radioactive iodine uptake test (RAIU) is also known as a thyroid uptake. ...

  4. Thyroid Scan and Uptake

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    Full Text Available Toggle navigation Test/Treatment Patient Type Screening/Wellness Disease/Condition Safety En Español More Info Images/Videos About Us News Physician Resources Professions Site Index A-Z Thyroid Scan and Uptake Thyroid scan and uptake uses ...

  5. Use of CdSe/ZnS luminescent quantum dots incorporated within sol-gel matrix for urea detection

    International Nuclear Information System (INIS)

    Duong, Hong Dinh; Rhee, Jong Il

    2008-01-01

    In this work, urea detection techniques based on the pH sensitivity of CdSe/ZnS QDs were developed using three types of sol-gel membranes: a QD-entrapped membrane, urease-immobilized membrane and double layer consisting of a QD-entrapped membrane and urease-immobilized membrane. The surface morphology of the sol-gel membranes deposited on the wells in a 24-well microtiter plate was investigated. The linear detection range of urea was in the range of 0-10 mM with the three types of sol-gel membranes. The urea detection technique based on the double layer consisting of the QD-entrapped membrane and urease-immobilized membrane resulted in the highest sensitivity to urea due to the Michaelis-Menten kinetic parameters. That is, the Michaelis-Menten constant (K m =2.0745 mM) of the free urease in the QD-entrapped membrane was about 4-fold higher than that (K m =0.549 mM) of the immobilized urease in the urease-immobilized membrane and about 12-fold higher than that (K m =0.1698 mM) of the immobilized urease in the double layer. The good stability of the three sol-gel membranes for urea sensing over 2 months showed that the use of sol-gel membranes immobilized with QDs or an enzyme is suitable for biomedical and environmental applications

  6. Use of CdSe/ZnS luminescent quantum dots incorporated within sol-gel matrix for urea detection.

    Science.gov (United States)

    Duong, Hong Dinh; Rhee, Jong Il

    2008-09-19

    In this work, urea detection techniques based on the pH sensitivity of CdSe/ZnS QDs were developed using three types of sol-gel membranes: a QD-entrapped membrane, urease-immobilized membrane and double layer consisting of a QD-entrapped membrane and urease-immobilized membrane. The surface morphology of the sol-gel membranes deposited on the wells in a 24-well microtiter plate was investigated. The linear detection range of urea was in the range of 0-10mM with the three types of sol-gel membranes. The urea detection technique based on the double layer consisting of the QD-entrapped membrane and urease-immobilized membrane resulted in the highest sensitivity to urea due to the Michaelis-Menten kinetic parameters. That is, the Michaelis-Menten constant (K(m)=2.0745mM) of the free urease in the QD-entrapped membrane was about 4-fold higher than that (K(m)=0.549mM) of the immobilized urease in the urease-immobilized membrane and about 12-fold higher than that (K(m)=0.1698mM) of the immobilized urease in the double layer. The good stability of the three sol-gel membranes for urea sensing over 2 months showed that the use of sol-gel membranes immobilized with QDs or an enzyme is suitable for biomedical and environmental applications.

  7. Crude Aloe vera Gel Shows Antioxidant Propensities and Inhibits Pancreatic Lipase and Glucose Movement In Vitro

    Science.gov (United States)

    Taukoorah, Urmeela; Mahomoodally, M. Fawzi

    2016-01-01

    Aloe vera gel (AVG) is traditionally used in the management of diabetes, obesity, and infectious diseases. The present study aimed to investigate the inhibitory potential of AVG against α-amylase, α-glucosidase, and pancreatic lipase activity in vitro. Enzyme kinetic studies using Michaelis-Menten (K m) and Lineweaver-Burk equations were used to establish the type of inhibition. The antioxidant capacity of AVG was evaluated for its ferric reducing power, 2-diphenyl-2-picrylhydrazyl hydrate scavenging ability, nitric oxide scavenging power, and xanthine oxidase inhibitory activity. The glucose entrapment ability, antimicrobial activity, and total phenolic, flavonoid, tannin, and anthocyanin content were also determined. AVG showed a significantly higher percentage inhibition (85.56 ± 0.91) of pancreatic lipase compared to Orlistat. AVG was found to increase the Michaelis-Menten constant and decreased the maximal velocity (V max) of lipase, indicating mixed inhibition. AVG considerably inhibits glucose movement across dialysis tubes and was comparable to Arabic gum. AVG was ineffective against the tested microorganisms. Total phenolic and flavonoid contents were 66.06 ± 1.14 (GAE)/mg and 60.95 ± 0.97 (RE)/mg, respectively. AVG also showed interesting antioxidant properties. The biological activity observed in this study tends to validate some of the traditional claims of AVG as a functional food. PMID:26880905

  8. Physisorption kinetics

    CERN Document Server

    Kreuzer, Hans Jürgen

    1986-01-01

    This monograph deals with the kinetics of adsorption and desorption of molecules physisorbed on solid surfaces. Although frequent and detailed reference is made to experiment, it is mainly concerned with the theory of the subject. In this, we have attempted to present a unified picture based on the master equation approach. Physisorption kinetics is by no means a closed and mature subject; rather, in writing this monograph we intended to survey a field very much in flux, to assess its achievements so far, and to give a reasonable basis from which further developments can take off. For this reason we have included many papers in the bibliography that are not referred to in the text but are of relevance to physisorption. To keep this monograph to a reasonable size, and also to allow for some unity in the presentation of the material, we had to omit a number of topics related to physisorption kinetics. We have not covered to any extent the equilibrium properties of physisorbed layers such as structures, phase tr...

  9. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... information about your thyroid’s size, shape, position and function that is often unattainable using other imaging procedures. ... thyroid uptake. It is a measurement of thyroid function, but does not involve imaging. Nuclear medicine is ...

  10. Thyroid Scan and Uptake

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    Full Text Available ... which are encased in metal and plastic and most often shaped like a box, attached to a ... will I experience during and after the procedure? Most thyroid scan and thyroid uptake procedures are painless. ...

  11. Thyroid Scan and Uptake

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    Full Text Available ... eat for several hours before your exam because eating can affect the accuracy of the uptake measurement. ... often unattainable using other imaging procedures. For many diseases, nuclear medicine scans yield the most useful information ...

  12. Thyroid Scan and Uptake

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    Full Text Available ... A thyroid scan is a type of nuclear medicine imaging. The radioactive iodine uptake test (RAIU) is ... thyroid function, but does not involve imaging. Nuclear medicine is a branch of medical imaging that uses ...

  13. Thyroid Scan and Uptake

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    Full Text Available ... Because nuclear medicine procedures are able to pinpoint molecular activity within the body, they offer the potential ... or imaging device that produces pictures and provides molecular information. The thyroid scan and thyroid uptake provide ...

  14. Thyroid Scan and Uptake

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    Full Text Available ... Actual scanning time for each thyroid uptake is five minutes or less. top of page What will ... diagnostic procedures have been used for more than five decades, and there are no known long-term ...

  15. Thyroid Scan and Uptake

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    Full Text Available ... top of page Additional Information and Resources RTAnswers.org Radiation Therapy for Head and Neck Cancer top ... Scan and Uptake Sponsored by Please note RadiologyInfo.org is not a medical facility. Please contact your ...

  16. Thyroid Scan and Uptake

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    Full Text Available ... When radiotracer is taken by mouth, in either liquid or capsule form, it is typically swallowed up ... radioactive iodine (I-123 or I-131) in liquid or capsule form to swallow. The thyroid uptake ...

  17. Thyroid Scan and Uptake

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    Full Text Available ... RAIU) is also known as a thyroid uptake. It is a measurement of thyroid function, but does ... they offer the potential to identify disease in its earliest stages as well as a patient’s immediate ...

  18. Thyroid Scan and Uptake

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    Full Text Available ... for several hours before your exam because eating can affect the accuracy of the uptake measurement. Jewelry ... small hand-held device resembling a microphone that can detect and measure the amount of the radiotracer ...

  19. Thyroid Scan and Uptake

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    Full Text Available ... of page What will I experience during and after the procedure? Most thyroid scan and thyroid uptake ... you otherwise, you may resume your normal activities after your nuclear medicine scan. If any special instructions ...

  20. Thyroid Scan and Uptake

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    Full Text Available ... scan and thyroid uptake provide information about the structure and function of the thyroid. The thyroid is ... computer, create pictures offering details on both the structure and function of organs and tissues in your ...

  1. Thyroid Scan and Uptake

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    Full Text Available ... eat for several hours before your exam because eating can affect the accuracy of the uptake measurement. ... its radioactivity over time. It may also pass out of your body through your urine or stool ...

  2. Thyroid Scan and Uptake

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    Full Text Available ... procedures within the last two months that used iodine-based contrast material. Your doctor will instruct you ... a type of nuclear medicine imaging. The radioactive iodine uptake test (RAIU) is also known as a ...

  3. Ammonium and hydroxylamine uptake and accumulation in Nitrosomonas

    NARCIS (Netherlands)

    Schmidt, I.; Look, C.; Bock, E.; Jetten, M.S.M.

    2004-01-01

    Starved cells of Nitrosomonas europaea and further ammonia oxidizers were able to rapidly accumulate ammonium and hydroxylamine to an internal concentration of about 1 and 0.8 M, respectively. In kinetic studies, the uptake/accumulation rates for ammonium [3.1 mmol (g protein)(-1) min(-1)] and

  4. Kinetic comparison of microbial assemblages for the anaerobic treatment of wastewater with high sulfate and heavy metal contents.

    Science.gov (United States)

    Sinbuathong, Nusara; Sirirote, Pramote; Liengcharernsit, Winai; Khaodhiar, Sutha; Watts, Daniel J

    2009-01-01

    Mixed-microbial assemblages enriched from a septic tank, coastal sediment samples, the digester sludge of a brewery wastewater treatment plant and acidic sulfate soil samples were compared on the basis of growth rate, waste and sulfate reduction rate under sulfate reducing conditions at 30 degrees C. The specific growth rate of various cultures was in the range 0.0013-0.0022 hr(-1). Estimates of waste and sulfate reduction rate were obtained by fitting substrate depletion and sulfate reduction data with the Michaelis-Menten equation. The waste reduction rates were in the range 4x10(-8)-1x10(-7) I mg(-1) hr(-1) and generally increased in the presence of copper, likely by copper sulfide precipitation that reduced sulfide and copper toxicity and thus protected the anaerobic microbes. Anaerobic microorganisms from a brewery digester sludge were found to be the most appropriate culture for the treatment of wastewater with high sulfate and heavy metal content due to their growth rate, and waste and sulfate reduction rate.

  5. Sensitivity analysis of a pulse nutrient addition technique for estimating nutrient uptake in large streams

    Science.gov (United States)

    Laurence Lin; J.R. Webster

    2012-01-01

    The constant nutrient addition technique has been used extensively to measure nutrient uptake in streams. However, this technique is impractical for large streams, and the pulse nutrient addition (PNA) has been suggested as an alternative. We developed a computer model to simulate Monod kinetics nutrient uptake in large rivers and used this model to evaluate the...

  6. Uptake of allochthonous dissolved organic matter from soil and salmon in coastal temperate rainforest streams

    Science.gov (United States)

    Jason B. Fellman; Eran Hood; Richard T. Edwards; Jeremy B. Jones

    2009-01-01

    Dissolved organic matter (DOM) is an important component of aquatic food webs. We compare the uptake kinetics for NH4-N and different fractions of DOM during soil and salmon leachate additions by evaluating the uptake of organic forms of carbon (DOC) and nitrogen (DON), and proteinaceous DOM, as measured by parallel factor (PARAFAC) modeling of...

  7. Uptake of mineral elements by plants

    International Nuclear Information System (INIS)

    Ven Babu, P.

    2008-01-01

    Scientific investigations into the mineral nutrition of plants, date back to the late 17th century and vast amount of literature has accumulated since then, encompassing the occurrence of mineral elements, their interaction in soil and within plants, kinetics of their uptake, role in metabolism, toxicity to plants and animals and so on. Despite great advances made in the fields of plant physiology, plant biochemistry and genetic engineering and application of sophisticated analytical and biochemical techniques, many aspects of nutrient uptake by plants, their movement within roots and the long distance transport to shoots remain yet to be fully answered and a combination of hypothesis and assumptions are taken into account, for understanding the phenomena. This write up deals with the subject in a brief and narrative manner, so as to enable the reader to get an insight into the field

  8. Inorganic phosphate uptake in unicellular eukaryotes.

    Science.gov (United States)

    Dick, Claudia F; Dos-Santos, André L A; Meyer-Fernandes, José R

    2014-07-01

    Inorganic phosphate (Pi) is an essential nutrient for all organisms. The route of Pi utilization begins with Pi transport across the plasma membrane. Here, we analyzed the gene sequences and compared the biochemical profiles, including kinetic and modulator parameters, of Pi transporters in unicellular eukaryotes. The objective of this review is to evaluate the recent findings regarding Pi uptake mechanisms in microorganisms, such as the fungi Neurospora crassa and Saccharomyces cerevisiae and the parasite protozoans Trypanosoma cruzi, Trypanosoma rangeli, Leishmania infantum and Plasmodium falciparum. Pi uptake is the key step of Pi homeostasis and in the subsequent signaling event in eukaryotic microorganisms. Biochemical and structural studies are important for clarifying mechanisms of Pi homeostasis, as well as Pi sensor and downstream pathways, and raise possibilities for future studies in this field. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Stochastic kinetics

    International Nuclear Information System (INIS)

    Colombino, A.; Mosiello, R.; Norelli, F.; Jorio, V.M.; Pacilio, N.

    1975-01-01

    A nuclear system kinetics is formulated according to a stochastic approach. The detailed probability balance equations are written for the probability of finding the mixed population of neutrons and detected neutrons, i.e. detectrons, at a given level for a given instant of time. Equations are integrated in search of a probability profile: a series of cases is analyzed through a progressive criterium. It tends to take into account an increasing number of physical processes within the chosen model. The most important contribution is that solutions interpret analytically experimental conditions of equilibrium (moise analysis) and non equilibrium (pulsed neutron measurements, source drop technique, start up procedures)

  10. Design of compounds having enhanced tumour uptake, using serum albumin as a carrier. Pt. 2

    International Nuclear Information System (INIS)

    Schilling, U.; Friedrich, E.A.; Sinn, H.; Schrenk, H.H.; Clorius, J.H.; Maier-Borst, W.

    1992-01-01

    In the present in vivo study the uptake kinetics of radioiodinated albumin were determined in normal organs, and tumours of rats using sequential scintigraphy. Results indicate that cellular uptake of the marker takes place. Fluorescence was not observed in muscle tissue. This appears to suggest that the albumin uptake is greater in tumours than in normal tissue, and that it is metabolized in the tumour cells. (Author)

  11. Tolrestat kinetics

    International Nuclear Information System (INIS)

    Hicks, D.R.; Kraml, M.; Cayen, M.N.; Dubuc, J.; Ryder, S.; Dvornik, D.

    1984-01-01

    The kinetics of tolrestat, a potent inhibitor of aldose reductase, were examined. Serum concentrations of tolrestat and of total 14 C were measured after dosing normal subjects and subjects with diabetes with 14 C-labeled tolrestat. In normal subjects, tolrestat was rapidly absorbed and disappearance from serum was biphasic. Distribution and elimination t 1/2s were approximately 2 and 10 to 12 hr, respectively, after single and multiple doses. Unchanged tolrestat accounted for the major portion of 14 C in serum. Radioactivity was rapidly and completely excreted in urine and feces in an approximate ratio of 2:1. Findings were much the same in subjects with diabetes. In normal subjects, the kinetics of oral tolrestat were independent of dose in the 10 to 800 mg range. Repetitive dosing did not result in unexpected cumulation. Tolrestat was more than 99% bound to serum protein; it did not compete with warfarin for binding sites but was displaced to some extent by high concentrations of tolbutamide or salicylate

  12. Oxygen uptake kinetics Of Pseudomonas sp. strain VB grown under ...

    African Journals Online (AJOL)

    Fred

    2004-07-22

    Jul 22, 2004 ... 1996). Its diverse uses makes the substance ubiquitous as an environmental xenobiotic which has considerable implications within the global biosphere. The microbial mixed cultural degradation of 2- methoxyethanol under anaerobic conditions has been reported (Tanaka et al., 1986; Tanaka and Pfennig,.

  13. Uptake and kinetic properties of choline and ethanolamine in ...

    African Journals Online (AJOL)

    Poracom

    metabolic reaction through the radioactivity signal. But not too high parasitaemia to get a dynamic and optimal growth of the parasite and avoid a high amount of lactic acid or other biological wastes that a high parasitaemia can release. It is the same caution that led to a relatively short incubation time (less than 240 min).

  14. Thyroid uptake software

    International Nuclear Information System (INIS)

    Alonso, Dolores; Arista, Eduardo

    2003-01-01

    The DETEC-PC software was developed as a complement to a measurement system (hardware) able to perform Iodine Thyroid Uptake studies. The software was designed according to the principles of Object oriented programming using C++ language. The software automatically fixes spectrometric measurement parameters and besides patient measurement also performs statistical analysis of a batch of samples. It possesses a PARADOX database with all information of measured patients and a help system with the system options and medical concepts related to the thyroid uptake study

  15. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available Toggle navigation Test/Treatment Patient Type Screening/Wellness Disease/Condition Safety En Español More Info Images/Videos About Us News Physician Resources Professions Site Index A-Z Thyroid Scan and Uptake ...

  16. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... information. The thyroid scan and thyroid uptake provide information about the structure and function of the thyroid. The thyroid is a gland in the neck that controls metabolism , a chemical process that regulates the rate at which the body ...

  17. Radioactive uptake by plants

    Energy Technology Data Exchange (ETDEWEB)

    Horak, O

    1986-01-01

    The fundamentals of radionuclide uptake by plants, both by leaves and roots are presented. Iodine, cesium, strontium and ruthenium are considered and a table of the measured concentrations in several agricultural plants shortly after the Chernobyl accident is presented. Another table gives the Cs and Sr transfer factors soil plants for some plants. By using them estimates of future burden can be obtained.

  18. Thyroid Scan and Uptake

    Medline Plus

    Full Text Available ... type your comment or suggestion into the following text box: Comment: E-mail: Area code: Phone no: ... of a typical probe counter used for thyroid uptake exams. The patient sits with the camera directed at the neck for five minutes, and then the leg for ...

  19. Thyroid Scan and Uptake

    Science.gov (United States)

    ... type your comment or suggestion into the following text box: Comment: E-mail: Area code: Phone no: ... of a typical probe counter used for thyroid uptake exams. The patient sits with the camera directed at the neck for five minutes, and then the leg for ...

  20. AIR POLLUTION FROM ANIMAL AND MUNICIPAL WASTEWATER: ASSESSMENT OF PRODUCTION AND RELEASE OF NOXIOUS GASES

    DEFF Research Database (Denmark)

    Dai, Xiaorong

    from animal manure (mixture of urine and feces) by hydrolysis of urinary urea catalyzed by microbial urease present in feces. To better understand the enzymatic process of ammonia formation in manure, experiments based on Michaelis-Menten kinetics were conducted to obtain accurate estimates...... of the kinetic parameters of urease activity of feces and manure from pig and cattle, and to investigate the effects of pH on animal fecal urease by individual ammonium generation rate determination at five pH levels. Investigating the gas production and release mechanisms is important not only for estimating...... characteristics of different types of wastes (e.g., the total nitrogen, total ammoniacal nitrogen, dry matter, and pH) had great influence on the releases of NH3, CO2, H2S, and SO2. The investigation of kinetic parameter showed that the maximum urease activity for pig feces is at around pH 7, while...

  1. A Biochemist's View of Ecosystem Rates and their Response to Changing Temperature

    Science.gov (United States)

    Arcus, V. L.

    2017-12-01

    Enzyme kinetics lie at the heart of biochemistry and the Michaelis-Menten equation that defines the relationship between substrate and rate is over 100 years old. About 80 years ago Eyring and Polyani formulated Transistion State Theory (TST) which describes the temperature-dependence of chemical reaction rates and the precise relationship between activation energy and the rate. TST provided a robust theoretical foundation for the Arrhenius equation and together, these equations are the foundation equations for the biochemist. Can these equations provide any insights into rates at larger scales, such as organism growth rates and those rates that interest ecosystem scientists (e.g. heterotrophic respiration, gross primary production)? Let us begin by considering a microbial cell. Microbial growth (i.e. cell division) requires the coordinated kinetics of thousands of enzymes including DNA/RNA polymerases, ribosomes, biosynthetic enzymes - all under a regime of highly complex regulatory effects. There is no a priori reason to expect that Michaelis-Menten kinetics and TST will adequately describe this vastly complex process. Indeed, Lloyd and Taylor showed 23 years ago that soil respiration is not well described by the Arrhenius function. More recently, Heskel and colleagues showed that leaf respiration is also not well described by the Arrhenius function. It is the same case for rates of photosynthesis. Despite this failure of the basic equations of biochemistry to map to biological rates at greater scales, what insights can biochemistry provide to ecosystem science? As nearly all of biological metabolism is mediated through enzyme kinetics, I will begin with the Michaelis-Menten equation under regimes of low and high substrate concentrations. This simplified view can provide surprising insights into processes at larger scales. I will also consider the relationship between the activation energy and the reaction rate. Many, many ecosystem-rate papers focus on the

  2. Uptake of exogenous spermidine by rat lungs perfused in situ

    International Nuclear Information System (INIS)

    Rannels, D.E.; Addison, J.L.

    1987-01-01

    Uptake of the polyamine spermidine (SPD) from the pulmonary circulation was characterized by using ventilated rat lungs perfused in situ with Krebs-Henseleit-bicarbonate buffer containing 4.5% bovine serum albumin, 5.6 mM glucose, and 20 amino acids at plasma levels. [ 14 C]SPD was accumulated by the lungs in a time- and concentration-dependent manner. The pathway of SPD uptake exhibited saturation kinetics with an apparent K/sub m/ in the range of 1 μM and a V/sub max/ of 450-540 pmol/g lung min. SPD uptake was inhibited by the naturally occurring polyamines putrescine and spermine (SPM) and by the inhibitor of polyamine synthesis, methyglyoxal bis(guanylhydrazone) (MGBG). Inhibition of SPD uptake by SPM followed competitive kinetics; although MGBG was also a competitive inhibitor of SPD uptake, MGBG was less effective than SPM. These observations indicate that SPD is taken up from the pulmonary circulation by a carrier-mediated pathway that is inhibited by other natural polyamines and by MGBG and exhibits by other natural polyamines and by MGBG and exhibits substrate affinity in the range of plasma SPD concentrations

  3. Uptake of exogenous spermidine by rat lungs perfused in situ

    Energy Technology Data Exchange (ETDEWEB)

    Rannels, D.E.; Addison, J.L.

    1987-01-01

    Uptake of the polyamine spermidine (SPD) from the pulmonary circulation was characterized by using ventilated rat lungs perfused in situ with Krebs-Henseleit-bicarbonate buffer containing 4.5% bovine serum albumin, 5.6 mM glucose, and 20 amino acids at plasma levels. (/sup 14/C)SPD was accumulated by the lungs in a time- and concentration-dependent manner. The pathway of SPD uptake exhibited saturation kinetics with an apparent K/sub m/ in the range of 1 ..mu..M and a V/sub max/ of 450-540 pmol/g lung min. SPD uptake was inhibited by the naturally occurring polyamines putrescine and spermine (SPM) and by the inhibitor of polyamine synthesis, methyglyoxal bis(guanylhydrazone) (MGBG). Inhibition of SPD uptake by SPM followed competitive kinetics; although MGBG was also a competitive inhibitor of SPD uptake, MGBG was less effective than SPM. These observations indicate that SPD is taken up from the pulmonary circulation by a carrier-mediated pathway that is inhibited by other natural polyamines and by MGBG and exhibits by other natural polyamines and by MGBG and exhibits substrate affinity in the range of plasma SPD concentrations.

  4. Characteristics of 36C103- influx into nitrate reductase deficient mutant E1 pisum sativum seedlings: evidence for restricted ''induction'' by nitrate compared with wild type

    International Nuclear Information System (INIS)

    Deane-Drummond, C.E.; Jacobsen, E.

    1986-01-01

    The characteristics of nitrate uptake into seedlings of Pisum sativum L. cv. Rondo mutant E 1 defective for nitrate reductase (NR) and of its parent variety Rondo have been investigated using 36 C10 3 - as an analogue for nitrate. The apparent Michaelis Menten constants (K m ) for 36 ClO 3 - influx measured over 10 min were similar for mutant E 1 and the wild type (Wt). There was a 28% increase in 36 C10 3 - into Wt seedlings following nitrate pretreatment but this was not found when mutant seedlings were used. N starvation increased 36 C10 3 - influx into both mutant and Wt seedlings, and the rate of cycling E/I was also enhanced to a similar extent. The results are discussed in terms of current ideas on the regulation of nitrate uptake and assimilation. (author)

  5. An evaluation of the inhibition of human butyrylcholinesterase and acetylcholinesterase by the organophosphate chlorpyrifos oxon

    International Nuclear Information System (INIS)

    Shenouda, Josephine; Green, Paula; Sultatos, Lester

    2009-01-01

    Acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) are enzymes that belong to the superfamily of α/β-hydrolase fold proteins. While they share many characteristics, they also possess many important differences. For example, whereas they have about 54% amino acid sequence identity, the active site gorge of acetylcholinesterase is considerably smaller than that of butyrylcholinesterase. Moreover, both have been shown to display simple and complex kinetic mechanisms, depending on the particular substrate examined, the substrate concentration, and incubation conditions. In the current study, incubation of butyrylthiocholine in a concentration range of 0.005-3.0 mM, with 317 pM human butyrylcholinesterase in vitro, resulted in rates of production of thiocholine that were accurately described by simple Michaelis-Menten kinetics, with a K m of 0.10 mM. Similarly, the inhibition of butyrylcholinesterase in vitro by the organophosphate chlorpyrifos oxon was described by simple Michaelis-Menten kinetics, with a k i of 3048 nM -1 h -1 , and a K D of 2.02 nM. In contrast to inhibition of butyrylcholinesterase, inhibition of human acetylcholinesterase by chlorpyrifos oxon in vitro followed concentration-dependent inhibition kinetics, with the k i increasing as the inhibitor concentration decreased. Chlorpyrifos oxon concentrations of 10 and 0.3 nM gave k i s of 1.2 and 19.3 nM -1 h -1 , respectively. Although the mechanism of concentration-dependent inhibition kinetics is not known, the much smaller, more restrictive active site gorge of acetylcholinesterase almost certainly plays a role. Similarly, the much larger active site gorge of butyrylcholinesterase likely contributes to its much greater reactivity towards chlorpyrifos oxon, compared to acetylcholinesterase.

  6. In vitro modulation of cytochrome P450 reductase supported indoleamine 2,3-dioxygenase activity by allosteric effectors cytochrome b(5) and methylene blue.

    Science.gov (United States)

    Pearson, Josh T; Siu, Sophia; Meininger, David P; Wienkers, Larry C; Rock, Dan A

    2010-03-30

    Indoleamine 2,3-dioxygenase (IDO) is a heme-containing dioxygenase involved in the degradation of several indoleamine derivatives and has been indicated as an immunosuppressive. IDO is an attractive target for therapeutic intervention in diseases which are known to capitalize on immune suppression, including cancer, HIV, and inflammatory diseases. Conventionally, IDO activity is measured through chemical reduction by the addition of ascorbate and methylene blue. Identification of potential coenzymes involved in the reduction of IDO in vivo should improve in vitro reconstitution systems used to identify potential IDO inhibitors. In this study we show that NADPH-cytochrome P450 reductase (CPR) is capable of supporting IDO activity in vitro and that oxidation of l-Trp follows substrate inhibition kinetics (k(cat) = 0.89 +/- 0.04 s(-1), K(m) = 0.72 +/- 0.15 microM, and K(i) = 9.4 +/- 2.0 microM). Addition of cytochrome b(5) to CPR-supported l-Trp incubations results in modulation from substrate inhibition to sigmoidal kinetics (k(cat) = 1.7 +/- 0.3 s(-1), K(m) = 1.5 +/- 0.9 microM, and K(i) = 1.9 +/- 0.3). CPR-supported d-Trp oxidations (+/-cytochrome b(5)) exhibit Michaelis-Menten kinetics. Addition of methylene blue (minus ascorbate) to CPR-supported reactions resulted in inhibition of d-Trp turnover and modulation of l-Trp kinetics from allosteric to Michaelis-Menten with a concurrent decrease in substrate affinity for IDO. Our data indicate that CPR is capable of supporting IDO activity in vitro and oxidation of tryptophan by IDO displays substrate stereochemistry dependent atypical kinetics which can be modulated by the addition of cytochrome b(5).

  7. Excitatory amino acid-stimulated uptake of 22Na+ in primary astrocyte cultures

    International Nuclear Information System (INIS)

    Kimelberg, H.K.; Pang, S.; Treble, D.H.

    1989-01-01

    In this study we have found that L-glutamic acid, as well as being taken up by a Na+-dependent mechanism, will stimulate the uptake of 22Na+ by primary astrocyte cultures from rat brain in the presence of ouabain. By simultaneously measuring the uptake of 22Na+ and L-3H-glutamate a stoichiometry of 2-3 Na+ per glutamate was measured, implying electrogenic uptake. Increasing the medium K+ concentration to depolarize the cells inhibited L-3H-glutamate uptake, while calculations of the energetics of the observed L-3H-glutamate accumulation also supported an electrogenic mechanism of at least 2 Na+:1 glutamate. In contrast, kinetic analysis of the Na+ dependence of L-3H-glutamate uptake indicated a stoichiometry of Na+ to glutamate of 1:1, but further analysis showed that the stoichiometry cannot be resolved by purely kinetic studies. Studies with glutamate analogs, however, showed that kainic acid was a very effective stimulant of 22Na+ uptake, but 3H-kainic acid showed no Na+ -dependent uptake. Furthermore, while L-3H-glutamate uptake was very sensitive to lowered temperatures, glutamate-stimulated 22Na+ uptake was relatively insensitive. These results indicate that glutamate-stimulated uptake of 22Na+ in primary astrocytes cultures cannot be explained solely by cotransport of Na+ with glutamate, and they suggest that direct kainic acid-type receptor induced stimulation of Na+ uptake also occurs. Since both receptor and uptake effects involve transport of Na+, accurate measurements of the Na+ :glutamate stoichiometry for uptake can only be done using completely specific inhibitors of these 2 systems

  8. Aza Cope Rearrangement of Propargyl Enammonium Cations Catalyzed By a Self-Assembled `Nanozyme

    Energy Technology Data Exchange (ETDEWEB)

    Hastings, Courntey J.; Fiedler, Dorothea; Bergman, Robert G.; Raymond, Kenneth N.

    2008-02-27

    The tetrahedral [Ga{sub 4}L{sub 6}]{sup 12-} assembly (L = N,N-bis(2,3-dihydroxybenzoyl)-1,5-diaminonaphthalene) encapsulates a variety of cations, including propargyl enammonium cations capable of undergoing the aza Cope rearrangement. For propargyl enammonium substrates that are encapsulated in the [Ga{sub 4}L{sub 6}]{sup 12-} assembly, rate accelerations of up to 184 are observed when compared to the background reaction. After rearrangement, the product iminium ion is released into solution and hydrolyzed allowing for catalytic turnover. The activation parameters for the catalyzed and uncatalyzed reaction were determined, revealing that a lowered entropy of activation is responsible for the observed rate enhancements. The catalyzed reaction exhibits saturation kinetics; the rate data obey the Michaelis-Menten model of enzyme kinetics, and competitive inhibition using a non-reactive guest has been demonstrated.

  9. Correlation analysis of reactivity in the oxidation of some organic diols by tripropylammonium fluorochromate in non-aqueous media

    Directory of Open Access Journals (Sweden)

    S. Sheik Mansoor

    2016-09-01

    Full Text Available The kinetics of oxidation of some organic diols by tripropylammonium fluorochromate (TriPAFC have been studied in dimethylsulfoxide (DMSO. The main product of oxidation is the corresponding hydroxy aldehydes. The reaction is first order with respect to TriPAFC and exhibited Michaelis-Menten type kinetics with respect to organic diols. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form: kobs = a + b[H+]. Various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of isokinetic relationship. Oxidation of diols was studied in 18 different organic solvents. The rate data are showing satisfactory correlation with Kamlet–Taft solvotochromic parameters (α, β and π∗. A suitable mechanism of oxidation has been proposed.

  10. A metabolic and pharmacokinetic comparison of theophylline and aminophylline (theophylline ethylenediamine).

    Science.gov (United States)

    Monks, T J; Smith, R L; Caldwell, J

    1981-02-01

    The metabolism and pharmacokinetics of intravenously administered theophylline and aminophylline (theophylline ethylenediamine) have been studied in 3 volunteers, using 14C-labelled theophylline. Both compounds were metabolized extensively and 1,3-dimethyluric acid, 1-methyluric acid, 3-methylxanthine and two unknown minor metabolites were excreted in the urine, in addition to theophylline. The elimination of theophylline, 1,3-dimethyluric acid, 1-methyluric acid and the unknown metabolites followed first-order kinetics, but that of 3-methylxanthine followed Michaelis-Menten kinetics. When given as aminophylline, theophylline was metabolized more rapidly and extensively than when given alone. The recovery of 14C in the urine was significantly higher after aminophylline than after theophylline. Abstention from intake of dietary methylxanthines for 7 days resulted in more rapid and extensive metabolism of aminophylline compared with results from the same subjects on their usual diets. The results indicate that, from a metabolic and pharmacokinetic viewpoint, aminophylline and theophylline are not equivalent.

  11. Analysis of mathematical modelling on potentiometric biosensors.

    Science.gov (United States)

    Mehala, N; Rajendran, L

    2014-01-01

    A mathematical model of potentiometric enzyme electrodes for a nonsteady condition has been developed. The model is based on the system of two coupled nonlinear time-dependent reaction diffusion equations for Michaelis-Menten formalism that describes the concentrations of substrate and product within the enzymatic layer. Analytical expressions for the concentration of substrate and product and the corresponding flux response have been derived for all values of parameters using the new homotopy perturbation method. Furthermore, the complex inversion formula is employed in this work to solve the boundary value problem. The analytical solutions obtained allow a full description of the response curves for only two kinetic parameters (unsaturation/saturation parameter and reaction/diffusion parameter). Theoretical descriptions are given for the two limiting cases (zero and first order kinetics) and relatively simple approaches for general cases are presented. All the analytical results are compared with simulation results using Scilab/Matlab program. The numerical results agree with the appropriate theories.

  12. Effect and Modeling of Glucose Inhibition and In Situ Glucose Removal During Enzymatic Hydrolysis of Pretreated Wheat Straw

    DEFF Research Database (Denmark)

    Andric, Pavle; Meyer, Anne S.; Jensen, Peter Arendt

    2010-01-01

    The enzymatic hydrolysis of lignocellulosic biomass is known to be product-inhibited by glucose. In this study, the effects on cellulolytic glucose yields of glucose inhibition and in situ glucose removal were examined and modeled during extended treatment of heat-pretreated wheat straw......, during 96 h of reaction. When glucose was removed by dialysis during the enzymatic hydrolysis, the cellulose conversion rates and glucose yields increased. In fact, with dialytic in situ glucose removal, the rate of enzyme-catalyzed glucose release during 48-72 h of reaction recovered from 20......-40% to become approximate to 70% of the rate recorded during 6-24 h of reaction. Although Michaelis-Menten kinetics do not suffice to model the kinetics of the complex multi-enzymatic degradation of cellulose, the data for the glucose inhibition were surprisingly well described by simple Michaelis...

  13. Catalytic Activity of μ-Carbido-Dimeric Iron(IV) Octapropylporphyrazinate in the 3,5,7,2',4'-Pentahydroxyflavone Oxidation Reaction with tert-Butyl Hydroperoxide

    Science.gov (United States)

    Tyurin, D. V.; Zaitseva, S. V.; Kudrik, E. V.

    2018-05-01

    It is found for the first time that μ-carbido-dimeric iron(IV) octapropylporphyrazinate displays catalytic activity in the oxidation reaction of natural flavonol morin with tert-butyl hydroperoxide, with the catalyst being stable under conditions of the reaction. The kinetics of this reaction are studied. It is shown the reaction proceeds via tentative formation of a complex between the catalyst and the oxidant, followed by O‒O bond homolytic cleavage. The kinetics of the reaction is described in the coordinates of the Michaelis-Menten equation. A linear dependence of the apparent reaction rate constant on the concentration of the catalyst is observed, testifying to its participation in the limiting reaction step. The equilibrium constants and rates of interaction are found. A mechanism is proposed for the reaction on the basis of the experimental data.

  14. Preparation of biosensors by immobilization of polyphenol oxidase in conducting copolymers and their use in determination of phenolic compounds in red wine.

    Science.gov (United States)

    Böyükbayram, A Elif; Kiralp, Senem; Toppare, Levent; Yağci, Yusuf

    2006-10-01

    Electrochemically produced graft copolymers of thiophene capped polytetrahydofuran (TPTHF1 and TPTHF2) and pyrrole were achieved by constant potential electrolysis using sodium dodecylsulfate (SDS) as the supporting electrolyte. Characterizations were based on Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Electrical conductivities were measured by the four-probe technique. Novel biosensors for phenolic compounds were constructed by immobilizing polyphenol oxidase (PPO) into conducting copolymers prepared by electropolymerization of pyrrole with thiophene capped polytetrahydrofuran. Kinetic parameters, maximum reaction rate (V(max)) and Michaelis-Menten constant (K(m)) and optimum conditions regarding temperature and pH were determined for the immobilized enzyme. Operational stability and shelf-life of the enzyme electrodes were investigated. Enzyme electrodes of polyphenol oxidase were used to determine the amount of phenolic compounds in two brands of Turkish red wines and found very useful owing to their high kinetic parameters and wide pH working range.

  15. Exosomes: Mechanisms of Uptake

    Directory of Open Access Journals (Sweden)

    Kelly J. McKelvey

    2015-07-01

    Full Text Available Exosomes are 30–100 nm microvesicles which contain complex cellular signals of RNA, protein and lipids. Because of this, exosomes are implicated as having limitless therapeutic potential for the treatment of cancer, pregnancy complications, infections, and autoimmune diseases. To date we know a considerable amount about exosome biogenesis and secretion, but there is a paucity of data regarding the uptake of exosomes by immune and non-immune cell types (e.g., cancer cells and the internal signalling pathways by which these exosomes elicit a cellular response. Answering these questions is of paramount importance.

  16. Exosomes: Mechanisms of Uptake

    Directory of Open Access Journals (Sweden)

    Kelly J. McKelvey

    2015-07-01

    Full Text Available Exosomes are 30–100 nm microvesicles which contain complex cellular signals of RNA, protein and lipids. Because of this, exosomes are implicated as having limitless therapeutic potential for the treatment of cancer, pregnancy complications, infections, and autoimmune diseases. To date we know a considerable amount about exosome biogenesis and secretion, but there is a paucity of data regarding the uptake of exosomes by immune and non- immune cell types (e.g., cancer cells and the internal signalling pathways by which these exosomes elicit a cellular response. Answering these questions is of para‐ mount importance.

  17. Heterogeneous Uptake of HO2 Radicals onto Atmospheric Aerosols

    Science.gov (United States)

    George, I. J.; Matthews, P. S.; Brooks, B.; Goddard, A.; Whalley, L. K.; Baeza-Romero, M. T.; Heard, D. E.

    2011-12-01

    The hydroxyl (OH) and hydroperoxyl (HO2) radicals, together known as HOx, play a vital role in atmospheric chemistry by controlling the oxidative capacity of the troposphere. The atmospheric lifetime and concentrations of many trace reactive species, such as volatile organic compounds (VOCs), are determined by HOx radical levels. Therefore, the ability to accurately predict atmospheric HOx concentrations from a detailed knowledge of their sources and sinks is a very useful diagnostic tool to assess our current understanding of atmospheric chemistry. Several recent field studies have observed significantly lower concentrations of HO2 radicals than predicted using box models, where HO2 loss onto aerosols was suggested as a possible missing sink [1, 2]. However, the mechanism on HO2 uptake onto aerosols and its impact on ambient HOx levels are currently not well understood. To improve our understanding of this process, we have conducted laboratory experiments to measure HO2 uptake coefficients onto submicron aerosol particles. The FAGE (Fluorescence Assay by Gas Expansion) technique, a highly sensitive laser induced fluorescence based detection method, was used to monitor HO2 uptake kinetics onto aerosol particles in an aerosol flow tube. The application of the FAGE technique allowed for kinetic experiments to be performed under low HO2 concentrations, i.e. [HO2] atomizing dilute salt solutions or by homogeneous nucleation. HO2 uptake coefficients (γ) have been measured for single-component solid and aqueous inorganic salt and organic aerosol particles with a wide range of hygroscopicities. HO2 uptake coefficients on solid particles were below the detection limit (γ < 0.001), whereas on aqueous aerosols uptake coefficients were somewhat larger (γ = 0.001 - 0.008). HO2 uptake coefficients were highest on aerosols containing metal ions, such as Cu and Fe. Humidity and aerosol pH did not significantly impact the reactive HO2 uptake. Preliminary experiments have also

  18. Bringing metabolic networks to life: convenience rate law and thermodynamic constraints

    Directory of Open Access Journals (Sweden)

    Klipp Edda

    2006-12-01

    Full Text Available Abstract Background Translating a known metabolic network into a dynamic model requires rate laws for all chemical reactions. The mathematical expressions depend on the underlying enzymatic mechanism; they can become quite involved and may contain a large number of parameters. Rate laws and enzyme parameters are still unknown for most enzymes. Results We introduce a simple and general rate law called "convenience kinetics". It can be derived from a simple random-order enzyme mechanism. Thermodynamic laws can impose dependencies on the kinetic parameters. Hence, to facilitate model fitting and parameter optimisation for large networks, we introduce thermodynamically independent system parameters: their values can be varied independently, without violating thermodynamical constraints. We achieve this by expressing the equilibrium constants either by Gibbs free energies of formation or by a set of independent equilibrium constants. The remaining system parameters are mean turnover rates, generalised Michaelis-Menten constants, and constants for inhibition and activation. All parameters correspond to molecular energies, for instance, binding energies between reactants and enzyme. Conclusion Convenience kinetics can be used to translate a biochemical network – manually or automatically - into a dynamical model with plausible biological properties. It implements enzyme saturation and regulation by activators and inhibitors, covers all possible reaction stoichiometries, and can be specified by a small number of parameters. Its mathematical form makes it especially suitable for parameter estimation and optimisation. Parameter estimates can be easily computed from a least-squares fit to Michaelis-Menten values, turnover rates, equilibrium constants, and other quantities that are routinely measured in enzyme assays and stored in kinetic databases.

  19. An Assessment of Factors Affecting Reactive Transport of Biodegradable BTEX in an Unconfined Aquifer System, Tehran Oil Refinery, Iran

    Directory of Open Access Journals (Sweden)

    A. Agah

    2012-12-01

    Full Text Available Risk-based assessment methods are commonly used at the contaminated sites by hydrocarbon pollutants. This paper presents the results of a two-dimensional finite volume model of reactive transport of biodegradable BTEX which have been developed for the saturated zone of an unconfined aquifer in the Pump station area of Tehran oil refinery, Iran. The model governing equations were numerically solved by modification of a general commercial software called PHOENICS. To reduce costs in general, many input parameters of a model are often approximated based on the used values in the contaminated sites with same conditions. It was not fully recognised the effect of errors in these inputs on modelling outputs. Thus, a sensitivity analysis was carried out to determine the influence of parameters variability on the results of model. For this analysis, the sensitivity of the model to changes in the dispersivity, distribution coefficient, parameters of Monod, Michaelis-Menten, first- and zero- order kinetics modes on the BTEX contaminant plume were examined by performing several simulations. It was found that the model is sensitive to changes in dispersivity and parameters of Michaelis-Menten, first- and zero- order kinetics model. On the other hand, the predictions for plumes assuming Monod kinetics are similar, even if different values for parameterization are chosen. The reason for this insensibility is that degradation is not limited by microbial kinetics in the simulation, but by dispersive mixing. Quantifying the effect of changes in model input parameters on the modelling results is essential when it is desired to recognise which model parameters are more vital on the fate and transport of reactive pollutants. Furthermore, this process can provide an insight into understanding pollutant transportation mechanisms.

  20. Direct measurement of catalase activity in living cells and tissue biopsies

    Energy Technology Data Exchange (ETDEWEB)

    Scaglione, Christine N.; Xu, Qijin; Ramanujan, V. Krishnan, E-mail: Ramanujanv@csmc.edu

    2016-01-29

    Spatiotemporal regulation of enzyme-substrate interactions governs the decision-making steps in biological systems. Enzymes, being functional units of every living cell, contribute to the macromolecular stability of cell survival, proliferation and hence are vital windows to unraveling the biological complexity. Experimental measurements capturing this dynamics of enzyme-substrate interactions in real time add value to this understanding. Furthermore these measurements, upon validation in realistic biological specimens such as clinical biopsies – can further improve our capability in disease diagnostics and treatment monitoring. Towards this direction, we describe here a novel, high-sensitive measurement system for measuring diffusion-limited enzyme-substrate kinetics in real time. Using catalase (enzyme) and hydrogen peroxide (substrate) as the example pair, we demonstrate that this system is capable of direct measurement of catalase activity in vitro and the measured kinetics follows the classical Michaelis-Menten reaction kinetics. We further demonstrate the system performance by measuring catalase activity in living cells and in very small amounts of liver biopsies (down to 1 μg total protein). Catalase-specific enzyme activity is demonstrated by genetic and pharmacological tools. Finally we show the clinically-relevant diagnostic capability of our system by comparing the catalase activities in liver biopsies from young and old mouse (liver and serum) samples. We discuss the potential applicability of this system in clinical diagnostics as well as in intraoperative surgical settings. - Highlights: • A novel, direct measurement of Catalase enzyme activity via, oxygen sensing method. • Steady-stateprofiles of Catalase activity follow the Michaelis-Menten Kinetics. • Catalase-specific activity demonstrated using genetic and pharmacological tools. • Overcomes limitations of spectroscopic methods and indirect calorimetric approaches. • Clear

  1. Direct measurement of catalase activity in living cells and tissue biopsies

    International Nuclear Information System (INIS)

    Scaglione, Christine N.; Xu, Qijin; Ramanujan, V. Krishnan

    2016-01-01

    Spatiotemporal regulation of enzyme-substrate interactions governs the decision-making steps in biological systems. Enzymes, being functional units of every living cell, contribute to the macromolecular stability of cell survival, proliferation and hence are vital windows to unraveling the biological complexity. Experimental measurements capturing this dynamics of enzyme-substrate interactions in real time add value to this understanding. Furthermore these measurements, upon validation in realistic biological specimens such as clinical biopsies – can further improve our capability in disease diagnostics and treatment monitoring. Towards this direction, we describe here a novel, high-sensitive measurement system for measuring diffusion-limited enzyme-substrate kinetics in real time. Using catalase (enzyme) and hydrogen peroxide (substrate) as the example pair, we demonstrate that this system is capable of direct measurement of catalase activity in vitro and the measured kinetics follows the classical Michaelis-Menten reaction kinetics. We further demonstrate the system performance by measuring catalase activity in living cells and in very small amounts of liver biopsies (down to 1 μg total protein). Catalase-specific enzyme activity is demonstrated by genetic and pharmacological tools. Finally we show the clinically-relevant diagnostic capability of our system by comparing the catalase activities in liver biopsies from young and old mouse (liver and serum) samples. We discuss the potential applicability of this system in clinical diagnostics as well as in intraoperative surgical settings. - Highlights: • A novel, direct measurement of Catalase enzyme activity via, oxygen sensing method. • Steady-stateprofiles of Catalase activity follow the Michaelis-Menten Kinetics. • Catalase-specific activity demonstrated using genetic and pharmacological tools. • Overcomes limitations of spectroscopic methods and indirect calorimetric approaches. • Clear

  2. Characterization of the human cytochrome P450 enzymes involved in the metabolism of dihydrocodeine

    Science.gov (United States)

    Kirkwood, L. C.; Nation, R. L.; Somogyi, A. A.

    1997-01-01

    Aims Using human liver microsomes from donors of the CYP2D6 poor and extensive metabolizer genotypes, the role of individual cytochromes P-450 in the oxidative metabolism of dihydrocodeine was investigated. Methods The kinetics of formation of N- and O-demethylated metabolites, nordihydrocodeine and dihydromorphine, were determined using microsomes from six extensive and one poor metabolizer and the effects of chemical inhibitors selective for individual P-450 enzymes of the 1A, 2A, 2C, 2D, 2E and 3A families and of LKM1 (anti-CYP2D6) antibodies were studied. Results Nordihydrocodeine was the major metabolite in both poor and extensive metabolizers. Kinetic constants for N-demethylation derived from the single enzyme Michaelis-Menten model did not differ between the two groups. Troleandomycin and erythromycin selectively inhibited N-demethylation in both extensive and poor metabolizers. The CYP3A inducer, α-naphthoflavone, increased N-demethylation rates. The kinetics of formation of dihydromorphine in both groups were best described by a single enzyme Michaelis-Menten model although inhibition studies in extensive metabolizers suggested involvement of two enzymes with similar Km values. The kinetic constants for O-demethylation were significantly different in extensive and poor metabolizers. The extensive metabolizers had a mean intrinsic clearance to dihydromorphine more than ten times greater than the poor metabolizer. The CYP2D6 chemical inhibitors, quinidine and quinine, and LKM1 antibodies inhibited O-demethylation in extensive metabolizers; no effect was observed in microsomes from a poor metabolizer. Conclusions CYP2D6 is the major enzyme mediating O-demethylation of dihydrocodeine to dihydromorphine. In contrast, nordihydrocodeine formation is predominantly catalysed by CYP3A. PMID:9431830

  3. Thyroid Uptake Measurement System

    International Nuclear Information System (INIS)

    Nguyen Duc Tuan; Nguyen Thi Bao My; Nguyen Van Sy

    2007-01-01

    The NED-UP.M7 is a complete thyroid uptake and analysis system specifically designed for nuclear medicine. Capable of performing a full range of studies this system provides fast, accurate results for Uptake Studies. The heart of the NED-UP.M7 is a microprocessor-controlled 2048 channel Compact Multi-Channel Analyzer, coupled to a 2 inch x 2 inch NaI(Tl) detector with a USB personal computer interface. The system offers simple, straight-forward operation using pre-programmed isotopes, and menudriven prompts to guide the user step by step through each procedure. The pre-programmed radionuclides include I-123, I-125, I-131, Tc-99m and Cs-137. The user-defined radionuclides also allow for isotope identification while the printer provides hard copy printouts for patient and department record keeping. The included software program running on PC (Windows XP-based) is a user friendly program with menudriven and graphic interface for easy controlling the system and managing measurement results of patient on Excel standard form. (author)

  4. Ammonium and nitrate uptake by the marine macrophytes Hypnea musciformis (Rhodophyta) and Macrocystis pyrifera (phaeophyta)

    Energy Technology Data Exchange (ETDEWEB)

    Haines, K.C. (Univ. of Texas Marine Science Inst., St. Croix, US Virgin Islands); Wheeler, P.A.

    1978-01-01

    NH/sub 4//sup +/ and NO/sub 3//sup -/ uptake were measured by continuous sampling with an autoanalyzer. For Hypnea musciformis (Wulfen) Lamouroux, NO/sub 3//sup -/ uptake followed saturable kinetics (K/sub s/ = 4.9 ..mu..g-at N.l/sup -1/, V/sub max/ = 2.85 ..mu..g-at N-g(wet)/sup -1/.h/sup -1/). The ammonium uptake data fit a truncated hyperbola, i.e., saturation was not reached at the concentrations used, NO/sub 3//sup -/ uptake was reduced one-half in the presence of NH/sub 4//sup +/, but presence of NO/sub 3//sup -/ had no effect on NH/sub 4//sup +/ uptake. Darkness reduced both NO/sub 3//sup -/ and NH/sub 4//sup +/ uptake by one-third to one-half. For Macrocystis pyrifera (L.) C. Agardh. NO/sub 3//sup -/ uptake followed saturable kinetics; K/sub s/ = 13.1 ..mu..g-at N.l/sup -1/, V/sub max/ = 3.05 ..mu..g-at N.g(wet)/sup -1/.h/sup -1/. NH/sub 4//sup +/ uptake showed saturable kinetics at concentrations below 22 ..mu..g-at N.l/sup -1/(K/sub s/ = 5.3 ..mu..g-at N.l/sup -1/, V/sub max/ = 2.38 ..mu..g-at N g(wet)/sup -1/.h/sup -1/); at higher concentrations uptake increased linearly with concentration. NO/sub 3//sup -/ and NH/sub 4//sup +/ were taken up simultaneously; presence of one form did not affect uptake of the other.

  5. Uptake and depuration of 131I by the edible periwinkle Littorina littorea: uptake from labelled seaweed (Chondrus crispus)

    International Nuclear Information System (INIS)

    Wilson, R.C.; Vives i Batlle, J.; McDonald, P.; Parker, T.G.

    2005-01-01

    Uptake and depuration experiments of 131 I from labelled seaweed (Chondrus crispus) by the edible periwinkle Littorina littorea have been performed. Radioiodine concentrations in winkles during uptake followed first-order kinetics with an uptake half-time of 1 day, and a calculated equilibrium concentration (C ∞ ) of 21 000 Bq kg -1 resulting in a transfer factor of 0.07 with respect to the labelled seaweed used as food. For depuration, a biphasic sequence with biological half-lives of 1 and 24 days was determined. The results suggest that in general, iodine turnover in periwinkles is slower than observed for other molluscs (monophasic biological half-lives in the order of 2-3 days). Both environmental media, food and seawater, can be significant sources of radioiodine for the winkle

  6. Cesium removal and kinetics equilibrium: Precipitation kinetics

    International Nuclear Information System (INIS)

    Barnes, M.J.

    1999-01-01

    This task consisted of both non-radioactive and radioactive (tracer) tests examining the influence of potentially significant variables on cesium tetraphenylborate precipitation kinetics. The work investigated the time required to reach cesium decontamination and the conditions that affect the cesium precipitation kinetics

  7. Identification of a single sinusoidal bile salt uptake system in skate liver

    International Nuclear Information System (INIS)

    Fricker, G.; Hugentobler, G.; Meier, P.J.; Kurz, G.; Boyer, J.L.

    1987-01-01

    To identify the sinusoidal bile acid uptake system(s) of skate liver, photoaffinity labeling and kinetic transport studies were performed in isolated plasma membranes as well as intact hepatocytes. In both preparations photoaffinity labeling with the photolabile bile salt derivative revealed the presence of a predominant bile salt binding polypeptide with an apparent molecular weight of 54,000. The [ 3 H]-labeling of this polypeptide was inhibited by taurocholate and cholate in a concentration-dependent manner and was virtually abolished by 1 mM of the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Kinetic studies of hepatic uptake with taurocholate, cholate, and the photoreactive bile salt derivative indicated the involvement of a single transport system, and all three substrates mutually competed with the uptake of each other. Finally, irreversible inhibition of the bile salt uptake system of photoaffinity labeling of hepatocytes with high concentrations of photolabile derivative reduced the V max but the K m of taurocholate uptake. These findings strongly indicate that a single polypeptide with an apparent molecular weight of 54,000 is involved in sinusoidal bile salt uptake into skate hepatocytes. These findings contrast with similar studies in rat liver that implicate both a 54,000- and 48,000-K polypeptide in bile salt uptake and are consistent with a single Na + -independent transport mechanism for hepatic bile salt uptake in this primitive vertebrate

  8. Kinetic modeling in pre-clinical positron emission tomography

    Energy Technology Data Exchange (ETDEWEB)

    Kuntner, Claudia [AIT Austrian Institute of Technology GmbH, Seibersdorf (Austria). Biomedical Systems, Health and Environment Dept.

    2014-07-01

    Pre-clinical positron emission tomography (PET) has evolved in the last few years from pure visualization of radiotracer uptake and distribution towards quantification of the physiological parameters. For reliable and reproducible quantification the kinetic modeling methods used to obtain relevant parameters of radiotracer tissue interaction are important. Here we present different kinetic modeling techniques with a focus on compartmental models including plasma input models and reference tissue input models. The experimental challenges of deriving the plasma input function in rodents and the effect of anesthesia are discussed. Finally, in vivo application of kinetic modeling in various areas of pre-clinical research is presented and compared to human data.

  9. Depuración aerobia de los efluentes resultantes del proceso de biometanización del alpechín

    Directory of Open Access Journals (Sweden)

    Borja Padilla, R.

    1992-02-01

    Full Text Available A study of aerobic treatment in batch regime of the effluents produced in the olive mill wastewater biomethanation process was carried out. An 83% of effluents organic substances was removal after the third day of fermentation. The substrate removal rate follows a zero-order kinetic for high concentrations, and a first-order kinetic for low organic matter concentration, during the last days of fermentation. The kinetic parameters (qmáx and K were obtained from Michaelis- Menten model.

    Se ha efectuado un estudio del proceso de depuración aerobia, en régimen discontinuo, de los efluentes procedentes del proceso de depuración anaerobia o biometanización del alpechín. Se comprueba que el 83% de la materia orgánica presente en este efluente se elimina a partir del tercer día de fermentación. La eliminación de sustrato sigue una cinética de orden cero para altas concentraciones del mismo y una cinética de primer orden para bajas concentraciones de materia orgánica, es decir, durante los últimos días de fermentación. Se aplica el modelo de Michaelis-Menten de eliminación de sustrato para la obtención de los parámetros cinéticos qmáx y Ks que rigen este proceso.

  10. Plasma kinetic theory

    International Nuclear Information System (INIS)

    Elliott, J.A.

    1993-01-01

    Plasma kinetic theory is discussed and a comparison made with the kinetic theory of gases. The plasma is described by a modified set of fluid equations and it is shown how these fluid equations can be derived. (UK)

  11. Quantification of nanowire uptake by live cells

    KAUST Repository

    Margineanu, Michael B.

    2015-05-01

    Nanostructures fabricated by different methods have become increasingly important for various applications at the cellular level. In order to understand how these nanostructures “behave” and for studying their internalization kinetics, several attempts have been made at tagging and investigating their interaction with living cells. In this study, magnetic iron nanowires with an iron oxide layer are coated with (3-Aminopropyl)triethoxysilane (APTES), and subsequently labeled with a fluorogenic pH-dependent dye pHrodo™ Red, covalently bound to the aminosilane surface. Time-lapse live imaging of human colon carcinoma HCT 116 cells interacting with the labeled iron nanowires is performed for 24 hours. As the pHrodo™ Red conjugated nanowires are non-fluorescent outside the cells but fluoresce brightly inside, internalized nanowires are distinguished from non-internalized ones and their behavior inside the cells can be tracked for the respective time length. A machine learning-based computational framework dedicated to automatic analysis of live cell imaging data, Cell Cognition, is adapted and used to classify cells with internalized and non-internalized nanowires and subsequently determine the uptake percentage by cells at different time points. An uptake of 85 % by HCT 116 cells is observed after 24 hours incubation at NW-to-cell ratios of 200. While the approach of using pHrodo™ Red for internalization studies is not novel in the literature, this study reports for the first time the utilization of a machine-learning based time-resolved automatic analysis pipeline for quantification of nanowire uptake by cells. This pipeline has also been used for comparison studies with nickel nanowires coated with APTES and labeled with pHrodo™ Red, and another cell line derived from the cervix carcinoma, HeLa. It has thus the potential to be used for studying the interaction of different types of nanostructures with potentially any live cell types.

  12. Threshold for extinction and survival in stochastic tumor immune system

    Science.gov (United States)

    Li, Dongxi; Cheng, Fangjuan

    2017-10-01

    This paper mainly investigates the stochastic character of tumor growth and extinction in the presence of immune response of a host organism. Firstly, the mathematical model describing the interaction and competition between the tumor cells and immune system is established based on the Michaelis-Menten enzyme kinetics. Then, the threshold conditions for extinction, weak persistence and stochastic persistence of tumor cells are derived by the rigorous theoretical proofs. Finally, stochastic simulation are taken to substantiate and illustrate the conclusion we have derived. The modeling results will be beneficial to understand to concept of immunoediting, and develop the cancer immunotherapy. Besides, our simple theoretical model can help to obtain new insight into the complexity of tumor growth.

  13. Model-Based Optimization of Scaffold Geometry and Operating Conditions of Radial Flow Packed-Bed Bioreactors for Therapeutic Applications

    Directory of Open Access Journals (Sweden)

    Danilo Donato

    2014-01-01

    Full Text Available Radial flow perfusion of cell-seeded hollow cylindrical porous scaffolds may overcome the transport limitations of pure diffusion and direct axial perfusion in the realization of bioengineered substitutes of failing or missing tissues. Little has been reported on the optimization criteria of such bioreactors. A steady-state model was developed, combining convective and dispersive transport of dissolved oxygen with Michaelis-Menten cellular consumption kinetics. Dimensional analysis was used to combine more effectively geometric and operational variables in the dimensionless groups determining bioreactor performance. The effectiveness of cell oxygenation was expressed in terms of non-hypoxic fractional construct volume. The model permits the optimization of the geometry of hollow cylindrical constructs, and direction and magnitude of perfusion flow, to ensure cell oxygenation and culture at controlled oxygen concentration profiles. This may help engineer tissues suitable for therapeutic and drug screening purposes.

  14. Modeling of an immobilized lipase tubular reactor for the production of glycerol and fatty acids from oils; Modelado de un reactor tubular de lipasas inmovilizadas para la produccion de glicerol y acidos grasos a partir de aceites

    Energy Technology Data Exchange (ETDEWEB)

    Oddone, S.; Grasselli, M.; Cuellas, A.

    2010-07-01

    Advances in the design of a bioreactor in the fats and oils industry have permitted the hydrolysis of triglycerides in mild conditions and improved productivity while avoiding the formation of unwanted byproducts. The present work develops a mathematical model that describes the hydrolytic activity of a tubular reactor with immobilized lipases for the production of glycerol and fatty acids from the oil trade. Runge Kuttas numerical method of high order has been applied, considering that there is no accumulation of the substratum in the surface of the membrane, where the enzyme is. At the same time, different equations based on the kinetic model of Michaelis Mentens and the Ping-Pong bi-bi mechanism were examined. Experimental data in discontinuous systems are the basis for the development of the quantitative mathematical model that was used to simulate the process computationally. The obtained results allow for optimizing both the operative variables and the economic aspects of industrial processes. (Author)

  15. Role of carboxydobacteria in consumption of atmospheric carbon monoxide by soil

    Energy Technology Data Exchange (ETDEWEB)

    Conrad, R. (Max-Planck-Institut fuer Chemie, Mainz, Germany); Meyer, O.; Seiler, W.

    1981-08-01

    The carbon monoxide consumption rates of the carboxydobacteria Pseudomonas (Seliberia) carboxydohydrogena, P. carboxydovorans, and P. carboxydoflava were measured at high (50%) and low (0.5 ..mu..l liter/sup -1/) mixing ratios of CO in air. CO was only consumed when the bacteria had been grown under CO-autotrophic conditions. At low cell densities the CO comsumption rates measured at low CO mixing ratios were similar in cell suspensions and in mixtures of bacteria in soil. CO consumption observed in natural soil (loess, eolian sand, chernozem) as well as in suspensions or soil mixtures of carboxydobacteria showed Michaelis-Menten kinetics. Considering the difference of the K/sub m/, values and the observed V/sub max/ values, carboxydobacteria cannot contribute significantly to the consumption of atmospheric CO.

  16. Response to a temperature modulation as a signature of chemical mechanisms.

    Science.gov (United States)

    Berthoumieux, H; Jullien, L; Lemarchand, A

    2007-11-01

    We consider n reactive species involved in unimolecular reactions and submitted to a temperature modulation of small amplitude. We determine the conditions on the rate constants for which the deviations from the equilibrium concentrations of each species can be optimized and find the analytical expression of the frequency associated with an extremum of concentration shift in the case n=3. We prove that the frequency dependence of the displacement of equilibrium gives access to the number n of species involved in the mechanism. We apply the results to the case of the transformation of a reactant into a product through a possible reactive intermediate and find the order relation obeyed by the activation energies of the different barriers. The results typically apply to enzymatic catalysis with kinetics of Michaelis-Menten type.

  17. Enantiomeric fractioning, degradation and metabolite formation of Mecoprop in subsoils with a phenoxy acid contamination history

    DEFF Research Database (Denmark)

    Frkova, Zuzana; Johansen, Anders; Karlson, Ulrich G.

    2015-01-01

    for their ability to degrade mecoprop under natural and amended conditions. Degradation of mecoprop was studied at elevated and environmentally relevant mecoprop concentrations as affected by nitrate and glucose at nitrate-reducing conditions and at a presence of oxygen (mimicking purging the soil with air. Results......As persistence and toxicity of the enantiomers of chiral pesticides are different a more comprehensive understanding of the fate of enantiomers of agrochemicals in the environment is necessary. Subsoils sampled vertically (2.5-6 m) at a site with a history of phenoxy acid contamination were used...... and enantioselectivity. Glucose hinders mecoprop degradation and changes the EF. Changing EF confirmed enzymatic dgradation of mecoprop in soils, which was well interpreted using the Michaelis-Menten kinetic model. The highest mecoprop degradation rate was measured in soils incubated at nitrate-reducing conditions...

  18. Evidence of enzymatic catalysis of oxygen reduction on stainless steels under marine biofilm.

    Science.gov (United States)

    Faimali, Marco; Benedetti, Alessandro; Pavanello, Giovanni; Chelossi, Elisabetta; Wrubl, Federico; Mollica, Alfonso

    2011-04-01

    Cathodic current trends on stainless steel samples with different surface percentages covered by biofilm and potentiostatically polarized in natural seawater were studied under oxygen concentration changes, temperature increases, and additions of enzymic inhibitors to the solution. The results showed that on each surface fraction covered by biofilm the oxygen reduction kinetics resembled a reaction catalyzed by an immobilised enzyme with high oxygen affinity (apparent Michaelis-Menten dissociation constant close to K(O(2))(M)  ≈ 10 μM) and low activation energy (W ≈ 20 KJ mole(-1)). The proposed enzyme rapidly degraded when the temperature was increased above the ambient (half-life time of ∼1 day at 25°C, and of a few minutes at 50°C). Furthermore, when reversible enzymic inhibitors (eg sodium azide and cyanide) were added, the cathodic current induced by biofilm growth was inhibited.

  19. Lipase-catalyzed ring-opening polymerization of lactones to polyesters and its mechanistic aspects.

    Science.gov (United States)

    Namekawa, S; Suda, S; Uyama, H; Kobayashi, S

    1999-01-01

    Lipase catalysis induced a ring-opening polymerization of lactones with different ring-sizes. Small-size (four-membered) and medium-size lactones (six- and seven-membered) as well as macrolides (12-, 13-, 16-, and 17-membered) were subjected to lipase-catalyzed polymerization. The polymerization behaviors depended primarily on the lipase origin and the monomer structure. The macrolides showing much lower anionic polymerizability were enzymatically polymerized faster than epsilon-caprolactone. The granular immobilized lipase derived from Candida antartica showed extremely efficient catalysis in the polymerization of epsilon-caprolactone. Single-step terminal functionalization of the polyester was achieved by initiator and terminator methods. The enzymatic polymerizability of lactones was quantitatively evaluated by Michaelis-Menten kinetics.

  20. Transformation frequency of γ irradiated plasmid DNA and the enzymatic double strand break formation by incubation in a protein extract of Escherichia coli

    International Nuclear Information System (INIS)

    Schulte-Frohlinde, D.; Mark, F.; Ventur, Y.

    1994-01-01

    It was found that incubation of γ-irradiated or DNaseI-treated plasmid DNA in a protein extract of Escherichia coli leads to enzyme-induced formation of double strand breaks (dsb) in competition with repair of precursors of these dsb. A survival curve of the plasmid DNA (as determined by transformation of E. coli) was calculated on the basis of enzyme-induced dsb as well as those produced by irradiation assuming that they are lethal. The calculated D O value was the same as that measured directly by transformation of irradiated plasmid DNA. Two models are presented that fit the experimental survival data as a function of dose. One is based on damage formation in the plasmid DNA including enzymatic conversion of single strand damage into dsb (U-model), the other is an enzymatic repair saturation model based on Michaelis-Menten kinetics. (Author)

  1. Cholesterol biosensor based on rf sputtered zinc oxide nanoporous thin film

    International Nuclear Information System (INIS)

    Singh, S. P.; Arya, Sunil K.; Pandey, Pratibha; Malhotra, B. D.; Saha, Shibu; Sreenivas, K.; Gupta, Vinay

    2007-01-01

    Cholesterol oxidase (ChOx) has been immobilized onto zinc oxide (ZnO) nanoporous thin films grown on gold surface. A preferred c-axis oriented ZnO thin film with porous surface morphology has been fabricated by rf sputtering under high pressure. Optical studies and cyclic voltammetric measurements show that the ChOx/ZnO/Au bioelectrode is sensitive to the detection of cholesterol in 25-400 mg/dl range. A relatively low value of enzyme's kinetic parameter (Michaelis-Menten constant) ∼2.1 mM indicates enhanced enzyme affinity of ChOx to cholesterol. The observed results show promising application of nanoporous ZnO thin film for biosensing application without any functionalization

  2. Synthetic, structural mimetics of the β-hairpin flap of HIV-1 protease inhibit enzyme function.

    Science.gov (United States)

    Chauhan, Jay; Chen, Shen-En; Fenstermacher, Katherine J; Naser-Tavakolian, Aurash; Reingewertz, Tali; Salmo, Rosene; Lee, Christian; Williams, Emori; Raje, Mithun; Sundberg, Eric; DeStefano, Jeffrey J; Freire, Ernesto; Fletcher, Steven

    2015-11-01

    Small-molecule mimetics of the β-hairpin flap of HIV-1 protease (HIV-1 PR) were designed based on a 1,4-benzodiazepine scaffold as a strategy to interfere with the flap-flap protein-protein interaction, which functions as a gated mechanism to control access to the active site. Michaelis-Menten kinetics suggested our small-molecules are competitive inhibitors, which indicates the mode of inhibition is through binding the active site or sterically blocking access to the active site and preventing flap closure, as designed. More generally, a new bioactive scaffold for HIV-1PR inhibition has been discovered, with the most potent compound inhibiting the protease with a modest K(i) of 11 μM. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. Characterization of lipase in reversed micelles formulated by Cibacron Blue F-3GA modified Span 85

    DEFF Research Database (Denmark)

    Zhang, Dong Hao; Guo, Zheng; Sun, Yan

    2007-01-01

    Sorbitan trioleate (Span 85) modified by Cibacron Blue F-3GA (CB) was prepared and used as an affinity surfactant to formulate a reversed micellar system for Candida rugosa lipase (CRL) solubilization. The system was characterized and evaluated by employing CRL-catalyzed hydrolysis of olive oil...... of the encapsulated lipase remained unchanged, but the apparent activity was significantly higher than that of the native enzyme in bulk solution. Kinetic studies indicated that the encapsulated lipase in the reversed micelles of CB-formulated Span 85 followed the Michaelis-Menten equation. The Michaelis constant...... was found to decrease with increasing surfactant concentration, suggesting an increase of the enzyme affinity for the substrate. Stability of the lipase in the reversed micelles was negatively correlated to W0. Introduction Reversed micelles are nanometer-scale transparent aggregates of water and surfactant...

  4. Statistical identifiability and convergence evaluation for nonlinear pharmacokinetic models with particle swarm optimization.

    Science.gov (United States)

    Kim, Seongho; Li, Lang

    2014-02-01

    The statistical identifiability of nonlinear pharmacokinetic (PK) models with the Michaelis-Menten (MM) kinetic equation is considered using a global optimization approach, which is particle swarm optimization (PSO). If a model is statistically non-identifiable, the conventional derivative-based estimation approach is often terminated earlier without converging, due to the singularity. To circumvent this difficulty, we develop a derivative-free global optimization algorithm by combining PSO with a derivative-free local optimization algorithm to improve the rate of convergence of PSO. We further propose an efficient approach to not only checking the convergence of estimation but also detecting the identifiability of nonlinear PK models. PK simulation studies demonstrate that the convergence and identifiability of the PK model can be detected efficiently through the proposed approach. The proposed approach is then applied to clinical PK data along with a two-compartmental model. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  5. A Solution of the Convective-Diffusion Equation for Solute Mass Transfer inside a Capillary Membrane Bioreactor

    Directory of Open Access Journals (Sweden)

    B. Godongwana

    2010-01-01

    Full Text Available This paper presents an analytical model of substrate mass transfer through the lumen of a membrane bioreactor. The model is a solution of the convective-diffusion equation in two dimensions using a regular perturbation technique. The analysis accounts for radial-convective flow as well as axial diffusion of the substrate specie. The model is applicable to the different modes of operation of membrane bioreactor (MBR systems (e.g., dead-end, open-shell, or closed-shell mode, as well as the vertical or horizontal orientation. The first-order limit of the Michaelis-Menten equation for substrate consumption was used to test the developed model against available analytical results. The results obtained from the application of this model, along with a biofilm growth kinetic model, will be useful in the derivation of an efficiency expression for enzyme production in an MBR.

  6. Sufficient conditions for optimality for a mathematical model of drug treatment with pharmacodynamics

    Directory of Open Access Journals (Sweden)

    Maciej Leszczyński

    2017-01-01

    Full Text Available We consider an optimal control problem for a general mathematical model of drug treatment with a single agent. The control represents the concentration of the agent and its effect (pharmacodynamics is modelled by a Hill function (i.e., Michaelis-Menten type kinetics. The aim is to minimize a cost functional consisting of a weighted average related to the state of the system (both at the end and during a fixed therapy horizon and to the total amount of drugs given. The latter is an indirect measure for the side effects of treatment. It is shown that optimal controls are continuous functions of time that change between full or no dose segments with connecting pieces that take values in the interior of the control set. Sufficient conditions for the strong local optimality of an extremal controlled trajectory in terms of the existence of a solution to a piecewise defined Riccati differential equation are given.

  7. Characterization of the anion sensitive ATPase in intact vacuoles of Kalanchoe diagremontiana

    Energy Technology Data Exchange (ETDEWEB)

    Kobza, J.; Uribe, E.G.

    1986-04-01

    A method for the isolation of intact vacuoles from K. daigremontiana was developed which produced high yields of relatively pure vacuoles as determined by marker enzyme contamination. Upon isolation, the vacuoles were stabilized by the inclusion of 5% (w/v) ficoll. Enzyme activity was insensitive to vanadate and azide but was strongly inhibited by DCCD. Enzyme activity was strictly dependent on the inclusion of Mg/sup 2 +/ and was stimulated by anions as depicted by the series, NO/sub 3//sup -/ < Br/sup -/ < SO/sub 4//sup -/ < HCO/sub 3//sup -/ < Cl/sup -/. It was found that in intact vacuoles the ATPase activity was stimulated by phosphate to a level equivalent to that found with the chloride. The enzyme exhibited Michaelis-Menten kinetics with a Km for Mg-ATP complex of 0.51 mM.

  8. Biodegradation of Benzene, Toluene, Ethylbenzene, and o-, m-, and p-Xylenes by the Newly Isolated Bacterium Comamonas sp. JB.

    Science.gov (United States)

    Jiang, Bei; Zhou, Zunchun; Dong, Ying; Tao, Wei; Wang, Bai; Jiang, Jingwei; Guan, Xiaoyan

    2015-07-01

    A bacterium designated strain JB, able to degrade six benzene, toluene, ethylbenzene, and o-, m-, and p-xylene (BTEX) compounds, was isolated from petroleum-contaminated soil. Taxonomic analyses showed that the isolate belonged to Comamonas, and until now, the genus Comamonas has not included any known BTEX degraders. The BTEX biodegradation rate was slightly low on the mineral salt medium (MSM), but adding a small amount of yeast extract greatly enhanced the biodegradation. The relationship between specific degradation rate and individual BTEX was described well by Michaelis-Menten kinetics. The treatment of petrochemical wastewater containing BTEX mixture and phenol was shown to be highly efficient by BTEX-grown JB. In addition, toxicity assessment indicated the treatment of the petrochemical wastewater by BTEX-grown JB led to less toxicity than untreated wastewater.

  9. Radioiodine uptake measurements in thyroid

    International Nuclear Information System (INIS)

    Kadireshn, A.; Kapur, S.C.; Samuel, J.R.; Mahajan, M.K.

    1988-01-01

    Evaluation of thyroid function can be carried out by measuring the uptake of orally administered radioactive iodine. The results of the thyroid uptake measurements for the period 1982-1987 in Christian Medical College, Ludhiana are presented here. About 3000 patients were screened during the analysis period. (author)

  10. Aquaporins and root water uptake

    Science.gov (United States)

    Water is one of the most critical resources limiting plant growth and crop productivity, and root water uptake is an important aspect of plant physiology governing plant water use and stress tolerance. Pathways of root water uptake are complex and are affected by root structure and physiological res...

  11. Uptake of nuclides by plants

    International Nuclear Information System (INIS)

    Greger, Maria

    2004-04-01

    This review on plant uptake of elements has been prepared to demonstrate how plants take up different elements. The work discusses the nutrient elements, as well as the general uptake and translocation in plants, both via roots and by foliar absorption. Knowledge of the uptake by the various elements within the periodic system is then reviewed. The work also discusses transfer factors (TF) as well as difficulties using TF to understand the uptake by plants. The review also focuses on species differences. Knowledge necessary to understand and calculate plant influence on radionuclide recirculation in the environment is discussed, in which the plant uptake of a specific nuclide and the fate of that nuclide in the plant must be understood. Plants themselves determine the uptake, the soil/sediment determines the availability of the nuclides and the nuclides themselves can interact with each other, which also influences the uptake. Consequently, it is not possible to predict the nuclide uptake in plants by only analysing the nuclide concentration of the soil/substrate

  12. Uptake of nuclides by plants

    Energy Technology Data Exchange (ETDEWEB)

    Greger, Maria [Stockholm Univ. (Sweden). Dept. of Botany

    2004-04-01

    This review on plant uptake of elements has been prepared to demonstrate how plants take up different elements. The work discusses the nutrient elements, as well as the general uptake and translocation in plants, both via roots and by foliar absorption. Knowledge of the uptake by the various elements within the periodic system is then reviewed. The work also discusses transfer factors (TF) as well as difficulties using TF to understand the uptake by plants. The review also focuses on species differences. Knowledge necessary to understand and calculate plant influence on radionuclide recirculation in the environment is discussed, in which the plant uptake of a specific nuclide and the fate of that nuclide in the plant must be understood. Plants themselves determine the uptake, the soil/sediment determines the availability of the nuclides and the nuclides themselves can interact with each other, which also influences the uptake. Consequently, it is not possible to predict the nuclide uptake in plants by only analysing the nuclide concentration of the soil/substrate.

  13. VO2 OFF TRANSIENT KINETICS IN EXTREME INTENSITY SWIMMING

    Directory of Open Access Journals (Sweden)

    Ana Sousa

    2011-09-01

    Full Text Available Inconsistencies about dynamic asymmetry between the on- and off- transient responses in oxygen uptake are found in the literature. Therefore, the purpose of this study was to characterize the oxygen uptake off-transient kinetics during a maximal 200-m front crawl effort, as examining the degree to which the on/off regularity of the oxygen uptake kinetics response was preserved. Eight high level male swimmers performed a 200-m front crawl at maximal speed during which oxygen uptake was directly measured through breath-by-breath oxymetry (averaged every 5 s. This apparatus was connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system. Results: The on- and off-transient phases were symmetrical in shape (mirror image once they were adequately fitted by a single-exponential regression models, and no slow component for the oxygen uptake response was developed. Mean (± SD peak oxygen uptake was 69.0 (± 6.3 mL·kg-1·min-1, significantly correlated with time constant of the off- transient period (r = 0.76, p < 0.05 but not with any of the other oxygen off-transient kinetic parameters studied. A direct relationship between time constant of the off-transient period and mean swimming speed of the 200-m (r = 0.77, p < 0.05, and with the amplitude of the fast component of the effort period (r = 0.72, p < 0.05 were observed. The mean amplitude and time constant of the off-transient period values were significantly greater than the respective on- transient. In conclusion, although an asymmetry between the on- and off kinetic parameters was verified, both the 200-m effort and the respectively recovery period were better characterized by a single exponential regression model

  14. Cadmium uptake by plants

    Energy Technology Data Exchange (ETDEWEB)

    Haghiri, F.

    1973-01-01

    Absorption of /sup 115m/Cd by soybean (Gylcine max l.) plants via foliar and root systems and translocation into the seed was determined. The uptake of /sup 115m/Cd by soybeans via the root system was more efficient than that of the foliar placement. Growth and Cd concentrations of soybean and wheat (Triticum aestivum l.) tops were influenced by soil-applied Cd. In both crops, the Cd concentration of plant tops increased while yield decreased with increasing levels of applied Cd. Cadmium toxicitiy began to occur in both crops at the lowest level of soil applied Cd (2.5 ppM). With soybean plants, Cd toxicity symptoms resembled fe chlorosis. For wheat plants there were no visual symptoms other than the studied growth. The relative concentration of Cd found in several vegetable crops varied depending on the plant species. The relative Cd concentration in descending order for various vegetables was lettuce (Lactuca sativa l.) > radish top (Raphanus sativus l.) > celery stalk (Apium graveolens l.) > celery leaves greater than or equal to green pepper (Capsicum frutescens l.) > radish roots.

  15. Concentration-dependent interactions of the organophosphates chlorpyrifos oxon and methyl paraoxon with human recombinant acetylcholinesterase

    International Nuclear Information System (INIS)

    Kaushik, R.; Rosenfeld, Clint A.; Sultatos, L.G.

    2007-01-01

    For many decades it has been thought that oxygen analogs (oxons) of organophosphorus insecticides phosphorylate the catalytic site of acetylcholinesterase by a mechanism that follows simple Michaelis-Menten kinetics. More recently, the interactions of at least some oxons have been shown to be far more complex and likely involve binding of oxons to a second site on acetylcholinesterase that modulates the inhibitory capacity of other oxon molecules at the catalytic site. The current study has investigated the interactions of chlorpyrifos oxon and methyl paraoxon with human recombinant acetylcholinesterase. Both chlorpyrifos oxon and methyl paraoxon were found to have k i 's that change as a function of oxon concentration. Furthermore, 10 nM chlorpyrifos oxon resulted in a transient increase in acetylthiocholine hydrolysis, followed by inhibition. Moreover, in the presence of 100 nM chlorpyrifos oxon, acetylthiocholine was found to influence both the K d (binding affinity) and k 2 (phosphorylation constant) of this oxon. Collectively, these results demonstrate that the interactions of chlorpyrifos oxon and methyl paraoxon with acetylcholinesterase cannot be described by simple Michaelis-Menten kinetics but instead support the hypothesis that these oxons bind to a secondary site on acetylcholinesterase, leading to activation/inhibition of the catalytic site, depending on the nature of the substrate and inhibitor. Additionally, these data raise questions regarding the adequacy of estimating risk of low levels of insecticide exposure from direct extrapolation of insecticide dose-response curves since the capacity of individual oxon molecules at low oxon levels could be greater than individual oxon molecules in vivo associated with the dose-response curve

  16. Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters.

    Science.gov (United States)

    Bristow, Laura A; Dalsgaard, Tage; Tiano, Laura; Mills, Daniel B; Bertagnolli, Anthony D; Wright, Jody J; Hallam, Steven J; Ulloa, Osvaldo; Canfield, Donald E; Revsbech, Niels Peter; Thamdrup, Bo

    2016-09-20

    A major percentage of fixed nitrogen (N) loss in the oceans occurs within nitrite-rich oxygen minimum zones (OMZs) via denitrification and anammox. It remains unclear to what extent ammonium and nitrite oxidation co-occur, either supplying or competing for substrates involved in nitrogen loss in the OMZ core. Assessment of the oxygen (O2) sensitivity of these processes down to the O2 concentrations present in the OMZ core (Chile at manipulated O2 levels between 5 nmol⋅L(-1) and 20 μmol⋅L(-1) Rates of both processes were detectable in the low nanomolar range (5-33 nmol⋅L(-1) O2), but demonstrated a strong dependence on O2 concentrations with apparent half-saturation constants (Kms) of 333 ± 130 nmol⋅L(-1) O2 for ammonium oxidation and 778 ± 168 nmol⋅L(-1) O2 for nitrite oxidation assuming one-component Michaelis-Menten kinetics. Nitrite oxidation rates, however, were better described with a two-component Michaelis-Menten model, indicating a high-affinity component with a Km of just a few nanomolar. As the communities of ammonium and nitrite oxidizers were similar to other OMZs, these kinetics should apply across OMZ systems. The high O2 affinities imply that ammonium and nitrite oxidation can occur within the OMZ core whenever O2 is supplied, for example, by episodic intrusions. These processes therefore compete with anammox and denitrification for ammonium and nitrite, thereby exerting an important control over nitrogen loss.

  17. Substrate uptake, phosphorus repression, and effect of seed culture on glycopeptide antibiotic production

    DEFF Research Database (Denmark)

    Maiti, Soumen K.; Singh, Kamaleshwar P.; Eliasson Lantz, Anna

    2010-01-01

    may experience catabolite repression by one or more of the substrates. Availability of reliable process models is a key bottleneck in optimization of such processes. Here we present a structured kinetic model to describe the growth, substrate uptake and product formation for the glycopeptide....... The model is also able to predict key phenomena such as simultaneous uptake of glucose and glycerol but with different specific uptake rates, and inhibition of glycopeptide production by high intracellular phosphate levels. The model is successfully applied to both production and seed medium with varying....... The model may have applications in optimizing seed transfer, medium composition, and feeding strategy for maximizing production....

  18. Defining Nitrogen Kinetics for Air Break in Prebreath

    Science.gov (United States)

    Conkin, Johnny

    2010-01-01

    Actual tissue nitrogen (N2) kinetics are complex; the uptake and elimination is often approximated with a single half-time compartment in statistical descriptions of denitrogenation [prebreathe(PB)] protocols. Air breaks during PB complicate N2 kinetics. A comparison of symmetrical versus asymmetrical N2 kinetics was performed using the time to onset of hypobaric decompression sickness (DCS) as a surrogate for actual venous N2 tension. METHODS: Published results of 12 tests involving 179 hypobaric exposures in altitude chambers after PB, with and without airbreaks, provide the complex protocols from which to model N2 kinetics. DCS survival time for combined control and airbreaks were described with an accelerated log logistic model where N2 uptake and elimination before, during, and after the airbreak was computed with a simple exponential function or a function that changed half-time depending on ambient N2 partial pressure. P1N2-P2 = (Delta)P defined decompression dose for each altitude exposure, where P2 was the test altitude and P1N2 was computed N2 pressure at the beginning of the altitude exposure. RESULTS: The log likelihood (LL) without decompression dose (null model) was -155.6, and improved (best-fit) to -97.2 when dose was defined with a 240 min half-time for both N2 elimination and uptake during the PB. The description of DCS survival time was less precise with asymmetrical N2 kinetics, for example, LL was -98.9 with 240 min half-time elimination and 120 min half-time uptake. CONCLUSION: The statistical regression described survival time mechanistically linked to symmetrical N2 kinetics during PBs that also included airbreaks. The results are data-specific, and additional data may change the conclusion. The regression is useful to compute additional PB time to compensate for an airbreak in PB within the narrow range of tested conditions.

  19. Defining Nitrogen Kinetics for Air Break in Prebreathe

    Science.gov (United States)

    Conkin, Johnny

    2009-01-01

    Actual tissue nitrogen (N2) kinetics are complex; the uptake and elimination is often approximated with a single half-time compartment in statistical descriptions of denitrogenation [prebreathe (PB)] protocols. Air breaks during PB complicate N2 kinetics. A comparison of symmetrical versus asymmetrical N2 kinetics was performed using the time to onset of hypobaric decompression sickness (DCS) as a surrogate for actual venous N2 tension. Published results of 12 tests involving 179 hypobaric exposures in altitude chambers after PB, with and without air breaks, provide the complex protocols from which to model N2 kinetics. DCS survival time for combined control and air breaks were described with an accelerated log logistic model where N2 uptake and elimination before, during, and after the air break was computed with a simple exponential function or a function that changed half-time depending on ambient N2 partial pressure. P1N2-P2 = delta P defined DCS dose for each altitude exposure, where P2 was the test altitude and P1N2 was computed N2 pressure at the beginning of the altitude exposure. The log likelihood (LL) without DCS dose (null model) was -155.6, and improved (best-fit) to -97.2 when dose was defined with a 240 min half-time for both N2 elimination and uptake during the PB. The description of DCS survival time was less precise with asymmetrical N2 kinetics, for example, LL was -98.9 with 240 min half-time elimination and 120 min half-time uptake. The statistical regression described survival time mechanistically linked to symmetrical N2 kinetics during PBs that also included air breaks. The results are data-specific, and additional data may change the conclusion. The regression is useful to compute additional PB time to compensate for an air break in PB within the narrow range of tested conditions.

  20. [14C]-Sucrose uptake by guard cell protoplasts of pisum sativum, argenteum mutant

    International Nuclear Information System (INIS)

    Rohrig, K.; Raschke, K.

    1991-01-01

    Guard cells rely on import for their supply with reduced carbon. The authors tested by silicone oil centrifugation the ability of guard cell protoplasts to accumulated [ 14 C]-sucrose. Uptake rates were corrected after measurement of 14 C-sorbitol and 3 H 2 O spaces. Sucrose uptake followed biphasic kinetics, with a high-affinity component below 1 mM external sucrose (apparent K m 0.8 mM at 25C) and a low-affinity nonsaturable component above. Uptake depended on pH (optimum at pH 5.0). Variations in the concentrations of external KCl, CCCP, and valinomycin indicated that about one-half of the sucrose uptake rate could be related to an electrochemical gradient across the plasmalemma. Total uptake rates measured at 5 mM external sucrose seem to be sufficient to replenish emptied plastids with starch within a few hours

  1. New Methods for Processing and Quantifying VO2 Kinetics to Steady State: VO2 Onset Kinetics

    Directory of Open Access Journals (Sweden)

    Craig R. McNulty

    2017-09-01

    Full Text Available Current methods of oxygen uptake (VO2 kinetics data handling may be too simplistic for the complex physiology involved in the underlying physiological processes. Therefore, the aim of this study was to quantify the VO2 kinetics to steady state across the full range of sub-ventilatory threshold work rates, with a particular focus on the VO2 onset kinetics. Ten healthy, moderately trained males participated in five bouts of cycling. Each bout involved 10 min at a percentage of the subject's ventilation threshold (30, 45, 60, 75, 90% from unloaded cycling. The VO2 kinetics was quantified using the conventional mono-exponential time constant (tau, τ, as well as the new methods for VO2 onset kinetics. Compared to linear modeling, non-linear modeling caused a deterioration of goodness of fit (main effect, p < 0.001 across all exercise intensities. Remainder kinetics were also improved using a modified application of the mono-exponential model (main effect, p < 0.001. Interestingly, the slope from the linear regression of the onset kinetics data is similar across all subjects and absolute exercise intensities, and thereby independent of subject fitness and τ. This could indicate that there are no functional limitations between subjects during this onset phase, with limitations occurring for the latter transition to steady state. Finally, the continuing use of mono-exponential modeling could mask important underlying physiology of more instantaneous VO2 responses to steady state. Consequently, further research should be conducted on this new approach to VO2 onset kinetics.

  2. Technetium uptake by Sinapis Alba

    International Nuclear Information System (INIS)

    Mueller, H.; Ter Meer-Bekk, Ch.

    1986-01-01

    Transfer factors for pertechnetate uptake was determined for Sinapis Alba cultured hydroponically. For the freshly harvested, undried plants transfer factors were found between 13 and 40 depending on the growth period. (author)

  3. Ethanol intake and 3H-serotonin uptake II: A study in alcoholic patients using platelets 3H-paroxetine binding

    International Nuclear Information System (INIS)

    Daoust, M.; Boucly, P.; Ernouf, D.; Breton, P.; Lhuintre, J.P.

    1991-01-01

    The kinetic parameters of 3 H-paroxetine binding and 3 H-serotonin uptake were studied in platelets of alcoholic patients. There was no difference between alcoholic and non alcoholic subjects in 3 H-paroxetine binding. When binding and 3 H-serotonin uptake were studied, in the same plasma of the same subjects, the Vmax of serotonin uptake was increased in alcoholics. The data confirm the involvement of serotonin uptake system in alcohol dependance and suggest that serotonin uptake and paroxetine binding sites may be regulated independently in this pathology

  4. Kinetic modeling in PET imaging of hypoxia

    Science.gov (United States)

    Li, Fan; Joergensen, Jesper T; Hansen, Anders E; Kjaer, Andreas

    2014-01-01

    Tumor hypoxia is associated with increased therapeutic resistance leading to poor treatment outcome. Therefore the ability to detect and quantify intratumoral oxygenation could play an important role in future individual personalized treatment strategies. Positron Emission Tomography (PET) can be used for non-invasive mapping of tissue oxygenation in vivo and several hypoxia specific PET tracers have been developed. Evaluation of PET data in the clinic is commonly based on visual assessment together with semiquantitative measurements e.g. standard uptake value (SUV). However, dynamic PET contains additional valuable information on the temporal changes in tracer distribution. Kinetic modeling can be used to extract relevant pharmacokinetic parameters of tracer behavior in vivo that reflects relevant physiological processes. In this paper, we review the potential contribution of kinetic analysis for PET imaging of hypoxia. PMID:25250200

  5. Principles of chemical kinetics

    CERN Document Server

    House, James E

    2007-01-01

    James House's revised Principles of Chemical Kinetics provides a clear and logical description of chemical kinetics in a manner unlike any other book of its kind. Clearly written with detailed derivations, the text allows students to move rapidly from theoretical concepts of rates of reaction to concrete applications. Unlike other texts, House presents a balanced treatment of kinetic reactions in gas, solution, and solid states. The entire text has been revised and includes many new sections and an additional chapter on applications of kinetics. The topics covered include quantitative rela

  6. Introduction to chemical kinetics

    CERN Document Server

    Soustelle, Michel

    2013-01-01

    This book is a progressive presentation of kinetics of the chemical reactions. It provides complete coverage of the domain of chemical kinetics, which is necessary for the various future users in the fields of Chemistry, Physical Chemistry, Materials Science, Chemical Engineering, Macromolecular Chemistry and Combustion. It will help them to understand the most sophisticated knowledge of their future job area. Over 15 chapters, this book present the fundamentals of chemical kinetics, its relations with reaction mechanisms and kinetic properties. Two chapters are then devoted to experimental re

  7. Diselenolane-mediated cellular uptake.

    Science.gov (United States)

    Chuard, Nicolas; Poblador-Bahamonde, Amalia I; Zong, Lili; Bartolami, Eline; Hildebrandt, Jana; Weigand, Wolfgang; Sakai, Naomi; Matile, Stefan

    2018-02-21

    The emerging power of thiol-mediated uptake with strained disulfides called for a move from sulfur to selenium. We report that according to results with fluorescent model substrates, cellular uptake with 1,2-diselenolanes exceeds uptake with 1,2-dithiolanes and epidithiodiketopiperazines with regard to efficiency as well as intracellular localization. The diselenide analog of lipoic acid performs best. This 1,2-diselenolane delivers fluorophores efficiently to the cytosol of HeLa Kyoto cells, without detectable endosomal capture as with 1,2-dithiolanes or dominant escape into the nucleus as with epidithiodiketopiperazines. Diselenolane-mediated cytosolic delivery is non-toxic (MTT assay), sensitive to temperature but insensitive to inhibitors of endocytosis (chlorpromazine, methyl-β-cyclodextrin, wortmannin, cytochalasin B) and conventional thiol-mediated uptake (Ellman's reagent), and to serum. Selenophilicity, the extreme CSeSeC dihedral angle of 0° and the high but different acidity of primary and secondary selenols might all contribute to uptake. Thiol-exchange affinity chromatography is introduced as operational mimic of thiol-mediated uptake that provides, in combination with rate enhancement of DTT oxidation, direct experimental evidence for existence and nature of the involved selenosulfides.

  8. Ontogeny of methionine utilization and splanchnic uptake in critically ill children

    Science.gov (United States)

    To determine the rates of methionine splanchnic uptake and utilization in critically ill pediatric patients, we used two kinetic models: the plasma methionine enrichment,and the "intracellular" homocysteine enrichment. Twenty-four patients, eight infants, eight children, and eight adolescents, were ...

  9. Interactive Influence of N and P on their uptake by four different ...

    African Journals Online (AJOL)

    The uptake kinetics of nitrogen (N) and phosphorus (P) by hydrophytes can be influenced by the interaction between N and P. In this study, Pistia stratiotes (a floating plant), Eichhornia crassipes (a floating plant), Vallisneria spiralis (a submerged plant), and Cyperus papyrus (an emergent plant) were selected to measure ...

  10. Sphagnum mosses : Masters of efficient N-uptake while avoiding intoxication

    NARCIS (Netherlands)

    Fritz, Christian; Lamers, Leon P.M.; Riaz, Muhammed; van den Berg, Leon J.L.; Elzenga, Theo J.T.M.

    2014-01-01

    Peat forming Sphagnum mosses are able to prevent the dominance of vascular plants under ombrotrophic conditions by efficiently scavenging atmospherically deposited nitrogen (N). N-uptake kinetics of these mosses are therefore expected to play a key role in differential N availability, plant

  11. Thallium kinetics in rat cardiac transplant rejection

    International Nuclear Information System (INIS)

    Barak, J.H.; LaRaia, P.J.; Boucher, C.A.; Fallon, J.T.; Buckley, M.J.

    1988-01-01

    Cardiac transplant rejection is a very complex process involving both cellular and vascular injury. Recently, thallium imaging has been used to assess acute transplant rejection. It has been suggested that changes in thallium kinetics might be a sensitive indicator of transplant rejection. Accordingly, thallium kinetics were assessed in vivo in acute untreated rat heterotopic (cervical) transplant rejection. Male Lewis rats weighing 225-250 g received heterotopic heart transplants from syngeneic Lewis rats (group A; n = 13), or allogeneic Brown Norway rats (group B; n = 11). Rats were imaged serially on the 2nd and the 7th postoperative days. Serial cardiac thallium content was determined utilizing data collected every 150 sec for 2 hr. The data were fit to a monoexponential curve and the decay rate constant (/sec) derived. By day 7 all group B hearts had histological evidence of severe acute rejection, and demonstrated decreased global contraction. Group A hearts showed normal histology and contractility. However, thallium uptakes and washout of the two groups were the same. Peak thallium uptake of group B was +/- 3758 1166 counts compared with 3553 +/- 950 counts in the control group A (P = 0.6395); The 2-hr percentage of washout was 12.1 +/- 1.04 compared with 12.1 +/- 9.3 (P = 1.0000); and the decay constant was -0.00002065 +/- 0.00001799 compared with -0.00002202 +/- 0.00001508 (P = 0.8409). These data indicate that in vivo global thallium kinetics are preserved during mild-to-severe acute transplant rejection. These findings suggest that the complex cellular and extracellular processes of acute rejection limit the usefulness of thallium kinetics in the detection of acute transplant rejection

  12. Effect of serum proteins on polystyrene nanoparticle uptake and intracellular trafficking in endothelial cells

    International Nuclear Information System (INIS)

    Guarnieri, Daniela; Guaccio, Angela; Fusco, Sabato; Netti, Paolo A.

    2011-01-01

    The physico-chemical properties of nanoparticles (NPs), such as small dimensions, surface charge and surface functionalization, control their capability to interact with cells and, in particular, with sub-cellular components. This interaction can be also influenced by the adsorption of molecules present in biological fluids, like blood, on NP surface. Here, we analysed the effect of serum proteins on 49 and 100 nm red fluorescent polystyrene NP uptake in porcine aortic endothelial (PAE) cells, as a model for vascular transport. To this aim, NP uptake kinetic, endocytic pathway and intracellular trafficking were studied by monitoring NPs inside cells through confocal microscopy and multiple particle tracking (MPT). We demonstrated that NPs are rapidly internalized by cells in serum-free (SF) medium, according to a saturation kinetic. Conversely, in 10% foetal bovine serum-enriched (SE) medium, NP uptake rate results drastically reduced. Moreover, NP internalization depends on an active endocytic mechanism that does not involve clathrin- and caveolae-mediated vesicular transport, in both SE and SF media. Furthermore, MPT data indicate that NP intracellular trafficking is unaffected by protein presence. Indeed, approximately 50–60% of internalized NPs is characterized by a sub-diffusive behaviour, whereas the remaining fraction shows an active motion. These findings demonstrate that the unspecific protein adsorption on NP surface can affect cellular uptake in terms of internalization kinetics, but it is not effective in controlling active and cellular-mediated uptake mechanisms of NPs and their intracellular routes.

  13. Exercise: Kinetic considerations for gas exchange.

    Science.gov (United States)

    Rossiter, Harry B

    2011-01-01

    The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease. © 2011 American Physiological Society.

  14. Substrate specificity and copper loading of the manganese-oxidizing multicopper oxidase Mnx from Bacillus sp. PL-12.

    Science.gov (United States)

    Butterfield, Cristina N; Tebo, Bradley M

    2017-02-22

    Manganese(ii) oxidation in the environment is thought to be driven by bacteria because enzymatic catalysis is many orders of magnitude faster than the abiotic processes. The heterologously purified Mn oxidase (Mnx) from marine Bacillus sp. PL-12 is made up of the multicopper oxidase (MCO) MnxG and two small Cu and heme-binding proteins of unknown function, MnxE and MnxF. Mnx binds Cu and oxidizes both Mn(ii) and Mn(iii), generating Mn(iv) oxide minerals that resemble those found on the Bacillus spore surface. Spectroscopic techniques have illuminated details about the metallo-cofactors of Mnx, but very little is known about their requirement for catalytic activity, and even less is known about the substrate specificity of Mnx. Here we quantify the canonical MCO Cu and persistent peripheral Cu bound to Mnx, and test Mnx oxidizing ability toward different substrates at varying pH. Mn(ii) appears to be the best substrate in terms of k cat , but its oxidation does not follow Michaelis-Menten kinetics, instead showing a sigmoidal cooperative behavior. Mnx also oxidizes Fe(ii) substrate, but in a Michaelis-Menten manner and with a decreased activity, as well as organic substrates. The reduced metals are more rapidly consumed than the larger organic substrates, suggesting the hypothesis that the Mnx substrate site is small and tuned for metal oxidation. Of biological relevance is the result that Mnx has the highest catalytic efficiency for Mn(ii) at the pH of sea water, especially when the protein is loaded with greater than the requisite four MCO copper atoms, suggesting that the protein has evolved specifically for Mn oxidation.

  15. Design of a new integrated chitosan-PAMAM dendrimer biosorbent for heavy metals removing and study of its adsorption kinetics and thermodynamics.

    Science.gov (United States)

    Zarghami, Zabihullah; Akbari, Ahmad; Latifi, Ali Mohammad; Amani, Mohammad Ali

    2016-04-01

    In this research, different generations of PAMAM-grafted chitosan as integrated biosorbents were successfully synthesized via step by step divergent growth approach of dendrimer. The synthesized products were utilized as adsorbents for heavy metals (Pb(2+) in this study) removing from aqueous solution and their reactive Pb(2+) removal potential was evaluated. The results showed that as-synthesized products with higher generations of dendrimer, have more adsorption capacity compared to products with lower generations of dendrimer and sole chitosan. Adsorption capacity of as-prepared product with generation 3 of dendrimer is 18times more than sole chitosan. Thermodynamic and kinetic studies were performed for understanding equilibrium data of the uptake capacity and kinetic rate uptake, respectively. Thermodynamic and kinetic studies showed that Langmuir isotherm model and pseudo second order kinetic model are more compatible for describing equilibrium data of the uptake capacity and kinetic rate of the Pb(2+) uptake, respectively. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Kinetic equation solution by inverse kinetic method

    International Nuclear Information System (INIS)

    Salas, G.

    1983-01-01

    We propose a computer program (CAMU) which permits to solve the inverse kinetic equation. The CAMU code is written in HPL language for a HP 982 A microcomputer with a peripheral interface HP 9876 A ''thermal graphic printer''. The CAMU code solves the inverse kinetic equation by taking as data entry the output of the ionization chambers and integrating the equation with the help of the Simpson method. With this program we calculate the evolution of the reactivity in time for a given disturbance

  17. Characteristics of sugar uptake by immature maize embryos

    International Nuclear Information System (INIS)

    Griffith, S.M.; Jones, R.J.; Brenner, M.L.

    1986-01-01

    Characteristics of sugar uptake by immature maize embryos were determined in vitro utilizing a 14 C-sugar solution incubation method. Hexose uptake rates were greater than those for sucrose, however, all showed biphasic kinetics. Glucose and fructose saturable components were evidence at <50 mM and sucrose at <5 mM. Chemical inhibitors (CCCP, DNP, NaCN, and PCMBS) and low temperature reduced sugar uptake. Sucrose influx was pH dependent while glucose was not. Embryos maintained a high sucrose to hexose ratio throughout development. At 25 days after pollination sucrose levels exceeded 200 mM while hexose levels remained below 5 mM. Glucose was rapidly converted to sucrose upon transport into the embryo. These circumstantial data indicate that sugar uptake by immature maize embryos is metabolically dependent and carrier mediated. Furthermore, sucrose transport appears to occur against its concentration gradient involving a H+/sucrose cotransport mechanism, while glucose influx is driven by its concentration gradient and subsequent metabolism

  18. Cerebral uptake of radioiodinated amphetamines - basic research and clinical results

    International Nuclear Information System (INIS)

    Biersack, H.J.; Kluenenberg, H.; Friedrich, G.; Knopp,