scholarly journals Effects of thimerosal on the transient kinetics of inositol 1,4,5-trisphosphate-induced Ca2+ release from cerebellar microsomes

1997 ◽  
Vol 325 (1) ◽  
pp. 177-182 ◽  
Author(s):  
Mokdad MEZNA ◽  
Francesco MICHELANGELI
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Slow Component ◽  
Kinetic Studies ◽  
Hill Coefficient ◽  
Slow Phase ◽  
Transient Kinetics ◽  
Exponential Process ◽  
Inositol 1,4,5 Trisphosphate ◽  
Two Phases

Thimerosal, a thiol-reactive reagent, has been shown to increase the cytosolic Ca2+ concentration in a variety of cells by sensitizing inositol 1,4,5-trisphosphate (InsP3) receptors. Thimerosal can have both sensitizing (at concentrations of < 2 μM) and inhibitory (at concentrations of > 2 μM) effects on InsP3-induced Ca2+ release (IICR) from cerebellar microsomes. Transient kinetic studies were performed by employing a fluorimetric stopped-flow approach using fluo-3. IICR was found to be a bi-exponential process with a fast and a slow component. At a maximal InsP3 concentration (20 μM), the fast phase had a rate constant of 0.9 s-1 and the slow phase had a rate constant of 0.4 s-1. The amplitudes of the two phases were 60% and 40% respectively. When the rate constants for the two phases were plotted as Hill plots, the processes were found to be non-co-operative in both cases (Hill coefficient of 1.0), thus arguing for a simple mechanism linking InsP3 binding to channel opening. At a submaximal InsP3 concentration (0.2 μM), where the sensitizing effects of thimerosal are most pronounced, thimerosal increased the rate constants of both phases in a sigmoidal fashion, with a Hill coefficient of 4.0, suggesting that several cysteine residues (up to four) need to be modified in order for maximum sensitization to occur. The rate constants remained elevated even at thimerosal concentrations that inhibited IICR. The amplitude or extent of Ca2+ release was, however, elevated to a much greater extent in the slow phase, suggesting that the two phases respond differently. At maximal InsP3 concentrations, thimerosal has no effect upon the rate constants but inhibits the amplitude of Ca2+ release.

Kinetic Studies on Antibody–Hapten Reactions. II. Reactions with Antibodies and their Polypeptide Chains

1973 ◽  
Vol 51 (10) ◽  
pp. 1355-1364 ◽  
Author(s):  
K. A. Kelly ◽  
A. H. Sehon ◽  
A. Froese
Keyword(s):  
Thin Layer ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Light Chains ◽  
Gel Chromatography ◽  
Equilibrium Studies ◽  
Polypeptide Chains

Kinetic and equilibrium studies were performed on the reactions of the hapten ε-dinitrophenyl-lysine with specific intact antibodies, reduced, alkylated, and polyalanylated antibodies, and reduced, alkylated, and polyalanylated γ-chains. No reaction was detected between the hapten and light chains. The γ-chains were found to have 0.5 combining sites per chain, and thin layer gel chromatography revealed that they existed as monomers. The rate constant of association for the reaction of γ-chains with hapten was found to be almost 1000 times lower than that for the corresponding reaction with the parent antibody. Differences in the rate constants of dissociation were much less pronounced. These results suggested that the combining site in the separated γ-chain had undergone a change in conformation.

scholarly journals A model for the passage of the neurohypophysial hormones and their related proteins through the rat neurohypophysis

1973 ◽  
Vol 136 (4) ◽  
pp. 1053-1058 ◽  
Author(s):  
Graham D. Burford ◽  
Peter Clifford ◽  
C. W. Jones ◽  
Brian T. Pickering
Keyword(s):  
Mathematical Models ◽  
Model Calculation ◽  
Rate Constant ◽  
Rate Constants ◽  
Exponential Process ◽  
Neurohypophysial Hormones ◽  
Releasable Pool ◽  
Readily Releasable Pool ◽  
Intracisternal Injection ◽  
Related Proteins

The change in the radioactivity of vasopressin–neurophysin in the rat neurohypophysis after an intracisternal injection of [35S]cysteine was fitted to several mathematical models. The data fitted best a model in which there is a linear input of radioactive protein into one pool of the neurohypophysis, from which it is either released by an exponential process or transferred to a second pool from which it is released by a second exponential process with a rate constant much lower than the first. This model is compatible with the existence of a ‘readily releasable’ pool first postulated by Sachs et al. (1967). Data for the change in radioactivity of vasopressin also gave a good fit in this model. Calculation of the rate constants suggested that the first pool represented about 2% of the total hormone.

scholarly journals The reactions of Pseudomonas cytochrome c-551 oxidase with potassium cyanide

1978 ◽  
Vol 175 (1) ◽  
pp. 239-249 ◽  
Author(s):  
D Barber ◽  
S R Parr ◽  
C Greenwood
Keyword(s):  
Cytochrome C ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Hill Coefficient ◽  
Spectral Studies ◽  
Slow Phase ◽  
Kinetic Measurements ◽  
Cyanide Concentration ◽  
Order Rate

The binding of cyanide to both oxidized and ascorbate-reduced forms of Pseudomonas cytochrome c-551 oxidase was investigated. Spectral studies on the oxidized enzyme and its apoprotein showed that the ligand can bind to both the c and d, haem components of the molecule, and kinetic observations indicated that both chromophores reacted, under a variety of conditions, with very similar rates. Cyanide combination velocities were dependent on ligand concentration, and increasing the pH also accelerated the reaction; the second-order rate constant was estimated as approx. 0.2M-1 . s-1 at pH 7.0. The binding of cyanide to the protein was observed to have a considerable influence on reduction of the enzyme by ascorbate. Spectral and kinetic observations have revealed that the species haem d13+-cyanide and any unbound haem c may react relatively rapidly with the reductant, but the behaviour of cyanide-bound haem c indicates that it may not be reduced without prior dissociation of the ligand, which occurs relatively slowly. The reaction of reduced Pseudomonas cytochrome oxidase with cyanide is radically different from that of the oxidized protein. In this case the ligand only binds to the haem d1 component and reacts much more rapidly. Stopped-flow kinetic measurements showed the binding to be biphasic in form. Both the rates of these processes were dependent on cyanide concentration, with the fast phase having a second-order rate constant of 9.3 × 10(5) M-1 . s-1 and the slow phase one of 2.3 × 10(5) M-1 . s-1. The relative proportions of the two phases also showed a dependency on cyanide concentration, the slower phase increasing as the cyanide concentration decreased. Computer simulations indicate that a reaction scheme originally proposed for the reaction of the enzyme with CO is capable of providing a reasonable explanation of the experimental results. Static-titration data of the reduced enzyme with with cyanide indicated that the binding was non-stoicheiometric, the ligand-binding curve being sigmoidal in shape. A Hill plot of the results yielded a Hill coefficient of 2.6.

Kinetics of oxidation of Cu(I) complexes of cysteine and penicillamine: nature of intermediates and reactants at pH 10.0

1989 ◽  
Vol 67 (4) ◽  
pp. 736-745 ◽  
Author(s):  
Stephen P. Mezyk ◽  
David A. Armstrong
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Rate Constants ◽  
Slow Component ◽  
Mixed Valence ◽  
Planar Geometry ◽  
Published Data ◽  
Diffusion Controlled ◽  
Square Planar ◽  
Thiolate Ligand

The Cu(I)•L2 complex with cysteine ligands at total Cu(I) concentrations of 10–30 μM was shown to be oxidised by cysteinyl radicals (RS•) with a diffusion-controlled rate constant k11a = 1.8 × 109 M−1 s−1. The corresponding reaction with the cysteine disulphide anion (RS•—SR−) proceeded at a slower rate, k11b = 2.7 × 108 M−1s−1. At higher Cu(I) concentrations, a slow and a fast component of absorption growth was observed. The slow component rate was independent of Cu(I) concentration, but it became more intense as the Cu(I) concentration rose. The yields and kinetic data were shown to be consistent with the presence of an equilibrium between the Cu(I)•L2 species and a second Cu(I) complex, Cu(I)2•L3, with an equilibrium constant of K1 = 162.[Formula: see text]This finding is consistent with the earlier work of Bagiyan etal. The rate constant of the oxidation of Cu(I)2•L3 by the cysteinyl radical was k12 = 1.0 × 109 M−1 s−1. Similar results were obtained with penicillamine, except the rate constants and equilibrium constant were smaller, (k11a = 4.5 × 108 M−1 s−1, k11b < 2 × 108 M−1 s−1, k12 = 5.5 × 108 M−1 s−1 and K1 = 113). This was attributed to the presence of the β-methyl groups in penicillamine, which exert a large steric effect.The ultraviolet spectra of the long-lived products, which are stable on a millisecond timescale, was consistent with a Cu(II)•L2 structure with a square planar geometry. The oxidation of the Cu(I)2.L3 species proceeded via intermediates, which relaxed to the final product spectra with rate constants of k13b = 2.6 and 1.1 × 104 s−1 for cysteine and penicillamine, respectively. Comparison of the spectra of the intermediates with published data showed that they were consistent with the presence of a bridging thiolate ligand between Cu(I) and Cu(II). Keywords: oxidation, copper, mixed valence, cysteine, penicillamine, complexation.

scholarly journals The carboxybiotin complex of chicken liver pyruvate carboxylase. A kinetic analysis of the effects of acetyl-CoA, Mg2+ ions and temperature on its stability and on its reaction with 2-oxobutyrate

1986 ◽  
Vol 235 (2) ◽  
pp. 359-364 ◽  
Author(s):  
P V Attwood ◽  
J C Wallace
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Protein Conformation ◽  
Pyruvate Carboxylase ◽  
Activation Parameters ◽  
Slow Phase ◽  
Acetyl Coa ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Pseudo First Order

The enzyme-[14C]carboxybiotin complex of chicken liver pyruvate carboxylase has been isolated and shown to be relatively stable, with a half-life at 0 degree C of 342 min. The kinetic properties of the decay of this complex, in both the presence and the absence of the substrate analogue, 2-oxobutyrate, have been examined. The data for the reaction with 2-oxobutyrate at 0 degree C fitted a biphasic exponential decay curve, enabling the calculation of rate constants for both the fast and slow phases of the reaction at this temperature. The effect of temperature on the observed pseudo-first-order rate constant for the slow phase of the reaction with 2-oxobutyrate, and that for the decay of the enzyme-[14C]carboxybiotin complex alone, have been examined. Arrhenius plots of these data revealed that the processes being studied in each type of experiment were single reactions represented by one rate constant in each case. For the decay of the enzyme-[14C]carboxybiotin complex in the absence of 2-oxobutyrate, the rate-determining process may be the movement of carboxybiotin from the site of the first partial reaction to the site of the second. The calculated thermodynamic activation parameters indicate that this reaction is accompanied by a large change in protein conformation. With 2-oxobutyrate present, the observed process in the slow phase of the reaction was probably the dissociation of the carboxybiotin from the first subsite. Here, the activation parameters suggest that a much smaller change in protein conformation accompanies this reaction. Both sets of experiments were also performed in the presence of acetyl-CoA, but this activator had little effect on the measured thermodynamic activation parameters. However, in both cases the observed pseudo-first-order rate constants in the presence of acetyl-CoA were about 75% of those in its absence. The effects of Mg2+ on the reaction kinetics of the enzyme-[14C]carboxybiotin complex with 2-oxobutyrate were similar to those observed with the sheep enzyme by Goodall, Baldwin, Wallace & Keech [(1981) Biochem. J. 199, 603-609].

PHOTO-INITIATED REACTIONS OF THIOLS AND OLEFINS: II. THE ADDITION OF METHANETHIOL TO UNCONJUGATED OLEFINS

1964 ◽  
Vol 42 (10) ◽  
pp. 2250-2255 ◽  
Author(s):  
D. M. Graham ◽  
R. L. Mieville ◽  
R. H. Pallen ◽  
C. Sivertz
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Addition Product ◽  
Isomerization Reaction ◽  
Ethylene Propylene ◽  
Intermittent Illumination ◽  
Competing Reactions

Kinetic studies have been made of the addition of methanethiol to ethylene, propylene, and butene-2. The results obtained are consistent with the mechanism postulated for the isomerization reaction (1). The overall activation energy was found to be negative and could be explained in terms of two competing reactions of the adduct radical: thermal decomposition leading to [Formula: see text] and olefin and dehydrogenation of thiol yielding addition product. Only the ratio of the rate constants for these two reactions could be determined. The method of intermittent illumination was used to evaluate the termination rate constant for the combination of two [Formula: see text] radicals which was found to be (2.5 ± 0.7) × 1010 l mole−1 s−1.

Vascular clearance and organ uptake of G- and F-actin in the rat

1993 ◽  
Vol 265 (6) ◽  
pp. G1071-G1081 ◽  
Author(s):  
A. J. Herrmannsdoerfer ◽  
G. T. Heeb ◽  
P. J. Feustel ◽  
J. E. Estes ◽  
C. J. Keenan ◽  
...  
Keyword(s):  
Kupffer Cells ◽  
Slow Component ◽  
Cell Uptake ◽  
Slow Phase ◽  
Organ Distribution ◽  
Rapid Phase ◽  
Time Constants ◽  
Clearance Kinetics ◽  
Two Phases

This study comparatively evaluated the kinetics of removal and organ distribution of circulating G- and F-actin. Both F- and G-actin were cleared in two phases (fast component with a t1/2 of 3-5 min and a slow component with a t1/2 of hours). There was no effect of dose on either the fast- or slow-compartment clearance kinetics at the doses tested (5-100 micrograms/100 g body wt). However, at the same challenging dose of F- and G-actin, more F-actin was removed during the rapid phase. Although the time constants (Tfast) for F- and G-actin removal from the vasculature during the initial rapid phase were the same, during the slow phase the time constants (Tslow) for removal of F-actin were less (P < 0.001) than that of G-actin. The fraction of F-actin removed during the rapid phase ranged from 33 to 63% and was significantly greater (P < 0.01) than the fraction of G-actin removed during this phase (10-33%). The liver was the main organ of localization, and autoradiographic studies of liver tissue demonstrated that G-actin monomers were removed by Kupffer cells, whereas F-actin was predominantly removed by hepatic sinusoidal endothelial cells. In vivo endotoxin activation of Kupffer cells enhanced the rate of G-actin removal and increased liver localization of G-actin but had no effect on F-actin removal. This further supports a role for Kupffer cells in the clearance of G-actin. These studies therefore demonstrate that F- and G-actin clearance mechanisms are different. G-actin removal, presumably mediated by its binding to vitamin D binding protein, is accomplished by Kupffer cells, whereas F-actin removal at the same doses is due mainly to hepatic endothelial cell uptake.

Determination of rate constants of redox reactions of second order from current-less potential-time curves by a simplified graphical-numerical method

1983 ◽  
Vol 48 (5) ◽  
pp. 1358-1367 ◽  
Author(s):  
Antonín Tockstein ◽  
František Skopal
Keyword(s):  
Numerical Method ◽  
Explicit Form ◽  
Rate Constant ◽  
Optimization Algorithm ◽  
Rate Constants ◽  
Redox Reactions ◽  
Second Order ◽  
Wide Region ◽  
Recurrent Formula

A method for constructing curves is proposed that are linear in a wide region and from whose slopes it is possible to determine the rate constant, if a parameter, θ, is calculated numerically from a rapidly converging recurrent formula or from its explicit form. The values of rate constants and parameter θ thus simply found are compared with those found by an optimization algorithm on a computer; the deviations do not exceed ±10%.

The Effect of p-Toluidine on the Two-Step Electroreduction of Zn(II) in Water-Methanol and Water-Dimethylformamide

1999 ◽  
Vol 64 (4) ◽  
pp. 585-594 ◽  
Author(s):  
Barbara Marczewska
Keyword(s):  
Electron Transfer ◽  
Binary Mixtures ◽  
Rate Constant ◽  
Rate Constants ◽  
Electrode Surface ◽  
Mercury Electrode ◽  
Forward Rate ◽  
Solvent Molecules ◽  
Activated Complex

The acceleration effect of p-toluidine on the electroreduction of Zn(II) on the mercury electrode surface in binary mixtures water-methanol and water-dimethylformamide is discussed. The obtained apparent and true forward rate constants of Zn(II) reduction indicate that the rate constant of the first electron transfer increases in the presence of p-toluidine. The acceleration effect may probably be accounted for by the concept of the formation on the mercury electrode an activated complex, presumably composed of p-toluidine and solvent molecules.

Radiolysis studies on the corrosion inhibitors 1 -hexyn-3-ol, cinnamonitrile, and 1,3-diethyl-2-thiourea

1995 ◽  
Vol 73 (12) ◽  
pp. 2137-2142 ◽  
Author(s):  
A.J. Elliot ◽  
M.P. Chenier ◽  
D.C. Ouellette
Keyword(s):  
Hydrogen Atom ◽  
Hydroxyl Radical ◽  
Temperature Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Corrosion Inhibitors ◽  
Hydrated Electron

In this publication we report: (i) the rate constants for reaction of the hydrated electron with 1-hexyn-3-ol ((8.6 ± 0.3) × 108 dm3 mol−1 s−1 at 18 °C), cinnamonitrile ((2.3 ± 0.2) × 1010 dm3 mol−1 s−1 at 20 °C), and 1,3-diethyl-2-thiourea ((3.5 ± 0.3) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile and diethylthiourea, the temperature dependence up to 200 °C and 150 °C, respectively, is also reported; (ii) the rate constants for the reaction of the hydroxyl radical with 1-hexyn-3-ol ((5.5 ± 0.5) × 109 dm3 mol−1 s−1 at 20 °C), cinnamonitrile ((9.2 ± 0.3) × 109 dm3 mol−1 s−1 at 21 °C), and diethylthiourea ((8.0 ± 0.8) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile, the temperature dependence up to 200 °C is also reported; (iii) the rate constant for the hydrogen atom reacting with 1-hexyn-3-ol ((4.3 ± 0.4) × 109 dm3 mol−1 s−1 at 20 °C). Keywords: radiolysis, corrosion inhibitors, rate constants.

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