scholarly journals Phosphoglucoisomerase-catalysed interconversion of hexose phosphates. Kinetic study by 13C n.m.r. of the phosphoglucoisomerase reaction in 2H2O

1990 ◽  
Vol 265 (2) ◽  
pp. 519-524 ◽  
Author(s):  
R Willem ◽  
F Malaisse-Lagae ◽  
R Ottinger ◽  
W J Malaisse
Keyword(s):  
Proton Transfer ◽  
Kinetic Study ◽  
Rate Constant ◽  
Rate Constants ◽  
Strong Support ◽  
Enzyme Concentration ◽  
Intermolecular Proton Transfer ◽  
Order Of Magnitude ◽  
Single Exponential ◽  
Hexose Phosphates

The fate of D-[2-13C]glucose 6-phosphate exposed to phosphoglucoisomerase (glucose-6-phosphate isomerase, EC 5.3.1.9) in 2H2O was monitored by 13C-n.m.r. spectroscopy. The generation of the anomers of both D-[2-13C]fructose 6-phosphate and D-[2-13C,2-2H]glucose 6-phosphate followed a single-exponential pattern. The rate constant, which was proportional to the enzyme concentration, was about 14 times higher, however, in the former than in the latter case. The disappearance of D-[2-13C,2-1H]glucose 6-phosphate occurred in a bi-exponential manner, the rate constants for the fast and the slow processes being in fair agreement with those obtained for the generation of D-[2-13C]fructose 6-phosphate and D-[2-13C,2-2H]glucose 6-phosphate respectively. These findings indicate that the process of equilibration of D-[2-13C]glucose 6-phosphate and D-[2-13C]fructose 6-phosphate is at least one order of magnitude faster than the intermolecular proton transfer involving the deuterons from the solvent. Such a difference provides strong support to the view that the inverconversion of hexose phosphates in the reaction catalysed by phosphoglucoisomerase proceeds in two distinct steps, the second of which occurs according to two competing modalities with either an intramolecular or an intermolecular proton transfer.

scholarly journals The Red Cell Chromium Elution Rate in Patients with Some Hematologic Diseases

Blood ◽  
1963 ◽  
Vol 21 (1) ◽  
pp. 63-69 ◽  
Author(s):  
MARTIN J. CLINE ◽  
NATHANIEL I. BERLIN
Keyword(s):  
Life Span ◽  
Rate Constant ◽  
Rate Constants ◽  
Red Cell ◽  
Hematologic Diseases ◽  
Cell Life ◽  
Elution Rate ◽  
Single Exponential

Abstract 1. The erythrocyte Cr51 elution rate was determined in 38 patients with hematologic diseases. 2. In four patients with finite red cell life spans, two exponential Cr51 elution rate constants could be calculated. In the remaining 34 patients, the data were consistent with a single exponential elution rate constant from day 1 to day 30-40 following Cr51 administration. 3. The single elution rate varied from 0.62 to 2.27 per cent per day. 4. In two patients, the chromium elution rates determined on two separate occasions were not significantly different. In a third individual, the chromium elution rate constant was 0.75 per cent per day when the red cell life span was 66 days and 1.07 per cent per day when red cell life span was 79 days.

scholarly journals Evolution of enzyme catalytic power. Characteristics of optimal catalysis evaluated for the simplest plausible kinetic model

1977 ◽  
Vol 163 (1) ◽  
pp. 111-116 ◽  
Author(s):  
Keith Brocklehurst
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Kinetic Mechanism ◽  
Enzyme Concentration ◽  
Forward Rate ◽  
Power Characteristics ◽  
Evolutionary Changes ◽  
Order Of Magnitude ◽  
Km Value

1. Evolutionary changes in the structure of an enzyme that provide an increase in its Km value are considered. Provided that Km increases as a result of increases in the forward rate constants of the catalysis relative to the reverse rate constants, the enzyme catalyses the conversion of a fixed concentration of its substrate more rapidly when its structure provides that Km>[S] than when Km<[S]. 2. Catalytic efficiency of enzymes is discussed in terms of the simplest plausible model, the Haldane [(1930) Enzymes, Longmans, London] reversible three-step model: [Formula: see text] The rate equation for the forward reaction of this model (formation of P) may be written in the simple form: [Formula: see text] Keq. is the equilibrium constant (=[P]eq./[S]eq.), and kcat.=V/[E]T, where [E]T is the total enzyme concentration. 3. To assess the effectiveness of an enzyme, it is necessary only to determine the extent to which the constraints of a particular kinetic mechanism permit v2 (v when Km»[S]) to approach vd (the diffusion-limited rate). 4. The value of the optimal rate of catalysis (vopt., the maximal value of v2) is dictated by the equilibrium constant for the reaction, Keq.; v2=vd/a, where [Formula: see text] when k+1 is assumed equal to k−3, and vopt.=vd/amin.. When Keq.≥1, it is necessary that k+2»k−1 for a to take its minimum value, amin.; when Keq.«1, it is necessary only that k+2»Keq.·k−1, i.e. a can equal amin. even if k+2<k−1. When Keq.»1, vopt.=vd; when Keq.=1, vopt.=vd/2, and when Keq.«1, vopt.=Keq.·vd. 5. The analysis, together with predicted effects of evolutionary pressure, suggests that in practice the rates of the fastest enzyme-catalysed freely reversible reactions might be expected to be lower than the value of k+1[E]T[S] by about an order of magnitude, particularly if Keq.<1. 6. The existing literature suggests that, in general, appropriate values of Km have evolved for the provision of high rates of catalysis but that many values of kcat. are not large enough to provide optimal rates of catalysis unless the value of k+1in vivo is lower than its value in free solution.

Intermolecular proton transfer in catalysis by carbonic anhydrase V

1999 ◽  
Vol 77 (5-6) ◽  
pp. 726-732 ◽  
Author(s):  
J Nicole Earnhardt ◽  
Chingkuang Tu ◽  
David N Silverman
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site ◽  
Rate Constants ◽  
Intramolecular Proton Transfer ◽  
Proton Donor ◽  
Marcus Theory ◽  
Intermolecular Proton Transfer ◽  
Donor And Acceptor ◽  
Active Site Cavity

The dehydration of bicarbonate catalyzed by carbonic anhydrase is accompanied by the transfer of a proton from solution to the zinc-bound hydroxide. We have investigated the properties of proton transfer from donors in solution, mostly derivatives of imidazole and pyridine, to a truncated mutant of carbonic anhydrase V with replacements that render the active site cavity less sterically constrained, Tyr 64 →> Ala and Phe 65 →> Ala. Catalysis was measured by determining the rate of exchange of 18O between the CO2-HCO3- system and water, and rate constants for proton transfer were estimated as the rate-limiting step in the release of H218O from the enzyme to solution. Each proton donor enhanced catalytic activity in a saturable manner. The resulting rate constants for proton transfer when compared with the values of pKa of the donor and acceptor gave a Brønsted plot of high curvature. These data could also be described by Marcus theory which showed an intrinsic barrier for intermolecular proton transfer near 0.8 kcal/mol and a work term or thermodynamic contribution to the free energy of reaction near 10 kcal/mol. This low intrinsic kinetic barrier for proton transfer is very similar to nonenzymic bimolecular proton transfer between nitrogen and oxygen acids and bases in solution. However, the significant thermodynamic contribution suggests appreciable involvement of solvent and active-site organization prior to proton transfer. These Marcus parameters are very similar to those describing intramolecular proton transfer from His 64 in carbonic anhydrase, suggesting similarities in the intra- and intermolecular proton transfer processes.Key words: carbonic anhydrase, proton transfer, Marcus theory, carbon dioxide.

Kinetic Study For The Formation Of The Oxygendeficient Magnetite

1994 ◽  
Vol 344 ◽  
Author(s):  
T. Togawa ◽  
Y. Wada ◽  
T. Yoshida ◽  
M. Tsuji ◽  
Y. Tamaura
Keyword(s):  
Partial Pressure ◽  
Kinetic Study ◽  
Rate Constant ◽  
Rate Constants ◽  
Arrhenius Equation ◽  
Reaction Order ◽  
Oxygen Deficiency ◽  
Reverse Reaction ◽  
Temperature Range ◽  
Reaction Orders

AbstractAn oxygendeficient magnetite (Fe3O4–8) has been found to exist in the range of (0<Δ<0.12) in the course of H2-reduction of magnetite to αFe at 300°C. The formation of the oxygendeficient magnetite was studied kinetically. In the temperature range of 250 350°C, the rate constants, k1, and k2, were determined for the forward and reverse reactions, respectively. The rate of formation of the oxygendeficient magnetite depended on the partial pressure of H2 gas. The rate constant, k1, was 109.58 at 300°C and the reaction order was 1.11 with respect to the partial pressure of H2 gas. The rate of reverse reaction depended on the partial pressure H2O gas and the oxygen deficiency of magnetite, Δ. The rate constant of the reverse reaction, k2, was 10−2.54 at 300°C, and the reaction orders were 0.45 and 0.99 with respect to the partial pressure of H2O gas and the Δ value respectively. The activation energies for the forward and reverse reactions were determined to be 63.8 kJ.mol−1 and 25.5 kJ.mol−1 from the Arrhenius' equation.

Potential energy construction in the diabatic picture for quantum mechanical rate constants of intermolecular proton transfer

2017 ◽  
Vol 19 (25) ◽  
pp. 16857-16866 ◽  
Author(s):  
Yuta Hori ◽  
Tomonori Ida ◽  
Motohiro Mizuno
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Quantum Dynamics ◽  
Transfer Reactions ◽  
Quantum Mechanical ◽  
Simple Method ◽  
Thermal Rate Constants ◽  
Intermolecular Proton Transfer ◽  
Proton Transfer Reactions ◽  
Dynamics Simulations

We propose a simple method for potential construction in the diabatic picture and the estimation of thermal rate constants for intermolecular proton transfer reactions using quantum dynamics simulations carried out on the constructed potentials.

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.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

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.

An ICR mass spectrometry study of ion/molecule reactions between ethyl chloride and alkylamines

1991 ◽  
Vol 69 (2) ◽  
pp. 363-367
Author(s):  
Guoying Xu ◽  
Jan A. Herman
Keyword(s):  
Mass Spectrometry ◽  
Key Words ◽  
Rate Constant ◽  
Rate Constants ◽  
Ethyl Chloride ◽  
Ion Molecule Reactions ◽  
Mass Spectrometry Study ◽  
Ethyl Cation

Ion/molecule reactions in mixtures of ethyl chloride with C1–C4 alkylamines were studied by ICR mass spectrometry. Ethyl cation transfer to C1–C4 alkylamines proceeds mainly through diethylchloronium ions with rate constants ~3 × 10−10cm3 s−1. In the case of s-butylamine the corresponding rate constant is 0.5 × 10−10 cm3 s−1. Key words: ICR mass spectrometry, ion/molecule reactions, ethylchloride, methylamine, ethylamine, propylamines, butylamines

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