scholarly journals Kinetics of activation and inactivation of swelling-stimulated K+/Cl- transport. The volume-sensitive parameter is the rate constant for inactivation.

1990 ◽  
Vol 95 (6) ◽  
pp. 1021-1040 ◽  
Author(s):  
M L Jennings ◽  
N al-Rohil
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Time Lag ◽  
Cell Swelling ◽  
Phosphatase Inhibitors ◽  
Kcl Transport ◽  
Lag Period ◽  
Activated Flux ◽  
Kinetics Of ◽  
Hypotonic Swelling

Red blood cells of several species are known to exhibit a ouabain-insensitive, anion-dependent K+ (Rb+) flux that is stimulated by cell swelling. We have used rabbit red cells to study the kinetics of activation and inactivation of the flux upon step changes in tonicity. Sudden hypotonic swelling (210 mosmol) activates the flux after a lag period of 10 min at 37 degrees C and 30-50 min at 25 degrees C. In cells that were preswollen to activate the transporter, sudden shrinkage (by addition of hypertonic NaCl) causes a rapid inactivation of the flux; the time lag for inactivation is less than 2 min at 37 degrees C. A minimal model of the volume-sensitive KCl transport system requires two states of the transporter. The activated (A) state catalyzes transport at some finite rate (turnover number unknown because the number of transporters is unknown). The resting (R) state has a much lower or possibly zero transport rate. The interconversion between the states is characterized by unimolecular rate constants R k12 in equilibrium with k21 A. The rate of relaxation to any new steady state is equal to the sum of the rate constants k12 + k21. Because the rate of transport activation in a hypotonic medium is lower than the rate of inactivation in an isotonic medium, we conclude that the volume-sensitive rate process is inactivation (the A to R transition); that is, cell swelling activates transport by lowering k21. Three phosphatase inhibitors (fluoride, orthovanadate, and inorganic phosphate) all inhibit the swelling-activated flux and also slow down the rate of approach to the swollen steady state. This finding suggests that a net dephosphorylation is necessary for activation of the flux and that the net dephosphorylation takes place as a result of swelling-induced inhibition of a kinase rather than stimulation of a phosphatase.

scholarly journals Determination of the steady-state turnover rates of the metabolically active pools of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate in human erythrocytes

1989 ◽  
Vol 259 (3) ◽  
pp. 893-896 ◽  
Author(s):  
C E King ◽  
P T Hawkins ◽  
L R Stephens ◽  
R H Michell
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Human Erythrocytes ◽  
Turnover Rates ◽  
Metabolic Fluxes ◽  
Metabolic Pool ◽  
Phosphatidylinositol 4 ◽  
Kinetics Of ◽  
Phosphate Groups

When intact human erythrocytes are incubated at metabolic steady state in a chloride-free medium containing [32P]Pi, there is rapid labelling of the gamma-phosphate of ATP, followed by a slower labelling of the monoester phosphate groups of phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] [King, Stephens, Hawkins, Guy & Michell (1987) Biochem. J. 244, 209-217]. We have analysed the early kinetics of the labelling of these phosphate groups, in order to determine: (a) the steady-state rates of the interconversions of phosphatidylinositol, PtdIns4P and PtdIns(4,5)P2; and (b) the fractions of the total cellular complement of PtdIns4P and PtdIns(4,5)P2 that participate in this steady-state turnover. The experimental data most closely fit a pattern of PtdIns4P and PtdIns(4,5)P2 turnover in which one-quarter of the total cellular complement of each lipid is in the metabolic pool that participates in rapid metabolic turnover, with rate constants of 0.028 min-1 for the interconversion of PtdIns and PtdIns4P, and of 0.010 min-1 for the PtdIns4P/PtdIns(4,5)P2 cycle. These rate constants represent metabolic fluxes of approx. 2.1 nmol of lipid/h per ml of packed erythrocytes between PtdIns and PtdIns4P and of approx. 5.7 nmol/h per ml of cells between PtdIns4P and PtdIns(4,5)P2.

Nucleation rates and the kinetics of particle growth II. The birth and death process

1964 ◽  
Vol 277 (1369) ◽  
pp. 167-182 ◽  
Keyword(s):  
Steady State ◽  
Homogeneous Nucleation ◽  
Time Lag ◽  
Particle Growth ◽  
Statistical Problem ◽  
Death Process ◽  
Birth And Death Process ◽  
Growth Mechanisms ◽  
Nucleation Kinetics ◽  
Kinetics Of

The model considered in part I is generalized to include growth mechanisms in which the chemical reaction which proceeds at the particle-atm osphere interface is reversible, so that molecules may evaporate from a particle as well as condense upon it. The Becker-Döring-Zeldovich-Frenkel theory of homogeneous nucleation kinetics is then reviewed in the light of the known statistical problem of the birth -and -death process, and an improved approximation is introduced which significantly alters the calculated results. Both steady-state nucleation kinetics and the time lag problem are discussed.

Measurements of adsorption for membranes in situ with the use of time-lags and steady state flows

1979 ◽  
Vol 365 (1722) ◽  
pp. 267-281 ◽  
Keyword(s):  
Steady State ◽  
Standard Procedure ◽  
Time Lag ◽  
Sorption Isotherms ◽  
Time Lags ◽  
Carbon Membrane ◽  
Differential Diffusion ◽  
Use Of Time ◽  
Kinetics Of

Isotherms, steady state flows, the four time-lags, the kinetics of sorption and of the approach to the steady state of flow have been measured and analysed to investigate the properties of a graphitized carbon membrane. Sorption isotherms determined on the membrane in situ by a kinetic pro­cedure involving the time-lags and steady state flows were in agreement with isotherms determined by a standard procedure. Analysis of the time-lag and other results left the possibility of a small dependence of the diffusion coefficient, D , upon positional coordinate or upon time, but the dominant influence upon D was its dependence upon concentration, C . Differential diffusion coefficients increased very rapidly with C outside the range of the Henry law. Uptakes of diffusant in the steady state of flow, measured directly, through time-lag measurements and from steady state concentration contours across the membrane were in good agreement.

Elimination rate constants of 36 PCBs in zebra mussels (Dreissena polymorpha) and exposure dynamics in the Lake St. Clair - Lake Erie corridor

1995 ◽  
Vol 52 (12) ◽  
pp. 2574-2582 ◽  
Author(s):  
Heather Morrison ◽  
Rodica Lazar ◽  
G. Douglas Haffner ◽  
Tamara Yankovich
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Dreissena Polymorpha ◽  
Lake Erie ◽  
Elimination Rate ◽  
Zebra Mussels ◽  
Elimination Kinetics ◽  
Western Lake ◽  
Order Of Magnitude ◽  
Kinetics Of

The elimination kinetics of 36 PCB congeners, ranging in log octanol–water partition coefficients (log Kow) from 5.60 to 7.50, were determined in zebra mussels (Dreissena polymorpha) with shell lengths from 1.0 to 1.5 cm. Elimination rate constants, based on lipid-normalized data, ranged from 0.172 to 0.042 day−1 and exhibited a significant negative regression with log Kow. Time to 95% steady state ranged from 17.5 to 71.0 days and was used to determine the period over which mussels integrated exposure concentrations. Bioavailable PCB congener concentrations, calculated with a steady-state model, were determined from mussels collected offshore of Middle Sister Island in western Lake Erie. Chemical concentrations in water, estimated using mussels, were within an order of magnitude of direct measurements for congeners with log Kow < 6.6. The rapid elimination kinetics of zebra mussels suggests that these organisms can closely track temporal fluctuations in ambient chemical concentrations, and therefore have the potential to regulate contaminant cycling in aquatic ecosystems.

A New Method for Determining Individual Rate Constants for Specific Non-chromophoric Substrates of Proteolytic Enzymes

1975 ◽  
Vol 53 (4) ◽  
pp. 564-571
Author(s):  
Lewis J. Brubacher
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Proteolytic Enzymes ◽  
Enzyme Mechanism ◽  
Steady State Kinetics ◽  
Steady State Rate ◽  
State Rate ◽  
Individual Rate ◽  
Kinetics Of ◽  
Hydrolysis Of

Equations are developed for the pre-steady state kinetics of the proteolytic enzyme-catalyzed hydrolysis of a substrate A in the presence of a monitoring substrate (or covalent inhibitor) S of known properties. A two-intermediate acyl–enzyme mechanism is assumed in which the first intermediate is in instantaneous equilibrium with enzyme and substrate. The appearance of the first product of substrate S is characterized by two relaxation rate constants. From these constants it is possible to determine the dissociation constant and the acylation and deacylation rate constants of substrate A. Criteria are also developed for using the steady state rate parameters of A to establish conditions for which the slower relaxation process is equivalent to the deacylation rate constant of A. The technique of premixing enzyme with substrate A has certain advantages in this approach.

The Kinetics of Efflux of 5,5-Dimethyl-2,4-Oxazolidinedione (DMO) from the Myocardium

1976 ◽  
Vol 51 (2) ◽  
pp. 197-201
Author(s):  
P. A. Poole-Wilson
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Rate Constants ◽  
Buffering Capacity ◽  
Distribution Volume ◽  
Steady State Distribution ◽  
State Distribution ◽  
Intracellular Compartments ◽  
Kinetics Of ◽  
Effluent Curve

1. The efflux of 14C-Iabelled 5,5-dimethyl-2,4-oxazolidinedione (DMO) from the myocardium of the rabbit has been studied. The perfusate pH was 7·38. 2. The effluent curve is complex and appears to be the resultant of movement between at least four compartments. 3. The first two probably represent intravascular and extracellular compartments; the last two have smaller rate constants and may represent intracellular spaces. Intracellular pH (pH1) calculated from the effluent curve was 7·23 ± 0·05. pH1 estimated from the steady-state distribution volume of DMO was 7·28 ± 0·02. 4. The existence of two intracellular compartments suggests that DMO is not homogeneously distributed in the myocardium. It is suggested that the apparent greater buffering capacity of cardiac than skeletal muscle can be explained by the greater number and volume of mitochondria in the myocardium, compartmentalization of DMO and assumptions inherent in the DMO method for the measurement of pH1.

scholarly journals Kinetics of the inhibition of human leucocyte elastase by eglin from the leech Hirudo medicinalis

1984 ◽  
Vol 218 (3) ◽  
pp. 829-833 ◽  
Author(s):  
A Baici ◽  
U Seemüller
Keyword(s):  
Steady State ◽  
Complex Formation ◽  
Rate Constants ◽  
Biological Significance ◽  
Hirudo Medicinalis ◽  
Inhibition Mechanism ◽  
Steady State Kinetic ◽  
Leucocyte Elastase ◽  
Kinetics Of ◽  
State Kinetic

The rate constants for the inhibition of human leucocyte elastase by eglin from the leech Hirudo medicinalis were determined by using a pre-steady-state kinetic approach. kon and koff for complex-formation and dissociation were 1 × 10(6)M-1 X S-1 and 8 × 10(-4)S-1 respectively. Ki was calculated as the ratio koff/kon = 8 × 10(-10)M, the binding of eglin to elastase was reversible and the inhibition mechanism was of the fully competitive type. The mechanistic properties of the system and the biological significance of the rate constants are discussed.

Submerged upflow biotower operation and computer simulation

1994 ◽  
Vol 30 (11) ◽  
pp. 143-146
Author(s):  
Ronald D. Neufeld ◽  
Christopher A. Badali ◽  
Dennis Powers ◽  
Christopher Carson
Keyword(s):  
Computer Simulation ◽  
Benzoic Acid ◽  
Computer Model ◽  
Rate Constants ◽  
Batch Mode ◽  
Operational Conditions ◽  
First Order ◽  
Low Concentrations ◽  
Biological Transformation ◽  
Kinetics Of

A two step operation is proposed for the biodegradation of low concentrations (&lt; 10 mg/L) of BETX substances in an up flow submerged biotower configuration. Step 1 involves growth of a lush biofilm using benzoic acid in a batch mode. Step 2 involves a longer term biological transformation of BETX. Kinetics of biotransformations are modeled using first order assumptions, with rate constants being a function of benzoic acid dosages used in Step 1. A calibrated computer model is developed and presented to predict the degree of transformation and biomass level throughout the tower under a variety of inlet and design operational conditions.

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