Determination of rate constants for disproportionation of semiquinone radicals in benzene using non-steady-state kinetics of chain reactions with participation of hydroquinones

2010 ◽  
Vol 434 (2) ◽  
pp. 180-184 ◽  
Author(s):  
S. Ya. Gadomsky ◽  
A. B. Ermatova ◽  
V. T. Varlamov
Keyword(s):  
Steady State ◽  
Rate Constants ◽  
Chain Reactions ◽  
Semiquinone Radicals ◽  
Steady State Kinetics ◽  
Kinetics Of

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.

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.

scholarly journals Steady-state kinetic analysis of aldehyde dehydrogenase from human erythrocytes

1992 ◽  
Vol 287 (1) ◽  
pp. 145-150 ◽  
Author(s):  
G T M Henehan ◽  
K F Tipton
Keyword(s):  
Steady State ◽  
Aldehyde Dehydrogenase ◽  
Initial Rate ◽  
Substrate Inhibition ◽  
Human Erythrocytes ◽  
Steady State Kinetics ◽  
Steady State Kinetic ◽  
Sequential Mechanism ◽  
Kinetics Of

The steady-state kinetics of purified cytoplasmic aldehyde dehydrogenase (EC 1.2.1.3) from human erythrocytes have been studied at 37 degrees C. Previous studies of the enzyme from several mammalian sources, which used a lower assay temperature, have been difficult to interpret because of the substrate activation by acetaldehyde which led to complex kinetic behaviour. At 37 degrees C the initial-rate data do not depart significantly from Michaelis-Menten kinetics. Studies of the variation of initial rates as a function of the concentrations of both substrates and studies of the inhibition by NADH were consistent with a sequential mechanism being followed. High-substrate inhibition by acetaldehyde was competitive with respect to NAD+. The enzyme was not inhibited by the product acetate and thus the results of these studies, although consistent with an ordered mechanism in which NAD+ was the first substrate to bind, were inconclusive. That such a mechanism was followed was confirmed by determination of the initial-rate behaviour in the presence of acetaldehyde and glycolaldehyde as alternative substrates. When the reciprocal of the initial rate of NADH formation was plotted against the acetaldehyde concentration at a series of fixed ratios between that substrate and glycolaldehyde, a linear ‘mixed inhibition’ pattern was obtained, confirming the mechanism to be ordered with NAD+ being the leading substrate and with kinetically significant ternary complex-formation.

Determination of the Nucleophilicity of Tricarbonyliron Coordinated Cyclohepta-1,3,5-triene

1999 ◽  
Vol 64 (11) ◽  
pp. 1770-1779 ◽  
Author(s):  
Herbert Mayr ◽  
Karl-Heinz Müller
Keyword(s):  
Gibbs Energy ◽  
Ambient Temperature ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Electrophilic Additions ◽  
Kinetics Of

The kinetics of the electrophilic additions of four diarylcarbenium ions (4a-4d) to tricarbonyl(η4-cyclohepta-1,3,5-triene)iron (1) have been studied photometrically. The second-order rate constants match the linear Gibbs energy relationship log k20 °C = s(E + N) and yield the nucleophilicity parameter N(1) = 3.69. It is concluded that electrophiles with E ≥ -9 will react with complex 1 at ambient temperature.

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