scholarly journals The linkage between binding of the C-terminal domain of hirudin and amidase activity in human α-thrombin

1993 ◽  
Vol 289 (2) ◽  
pp. 475-480 ◽  
Author(s):  
R de Cristofaro ◽  
B Rocca ◽  
B Bizzi ◽  
R Landolfi
Keyword(s):  
Rate Constants ◽  
Binding Constant ◽  
Amidase Activity ◽  
Equilibrium Binding ◽  
Viscosity Effects ◽  
The Individual ◽  
Individual Rate ◽  
Hydrolysis Of ◽  
Equilibrium Binding Constant

A method derived from the analysis of viscosity effects on the hydrolysis of the amide substrates D-phenylalanylpipecolyl-arginine-p-nitroaniline, tosylglycylprolylarginine-p-nitroanaline and cyclohexylglycylalanylarginine-p-nitroalanine by human alpha-thrombin was developed to dissect the Michaelis-Menten parameters Km and kcat into the individual rate constants of the binding, acylation and deacylation reactions. This method was used to analyse the effect of the C-terminal hirudin (residues 54-65) [hir-(54-65)] domain on the binding and hydrolysis of the three substrates. The results showed that the C-terminal hir-(54-65) fragment affects only the acylation rate, which is increased approx. 1.2-fold for all the substrates. Analysis of the dependence of acylation rate constants on hirudin-fragment concentration, allowed the determination of the equilibrium binding constant of C-terminal hir-(54-65) (Kd approximately 0.7 microM). In addition this peptide was found to competitively inhibit thrombin-fibrinogen interaction with a Ki which is in excellent agreement with the equilibrium constant derived from viscosity experiments. These results demonstrate that binding of hir-(54-65) to the fibrinogen recognition site of thrombin does not affect the equilibrium binding of amide substrates, but induces only a small increase in the acylation rate of the hydrolysis reaction.

scholarly journals Isomerization of an enzyme-coenzyme complex in yeast alcohol dehydrogenase-catalysed reactions

2003 ◽  
Vol 68 (2) ◽  
pp. 77-84 ◽  
Author(s):  
Vladimir Leskovac ◽  
Svetlana Trivic ◽  
Draginja Pericin
Keyword(s):  
Alcohol Dehydrogenase ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Kinetic Mechanism ◽  
Yeast Alcohol Dehydrogenase ◽  
Catalyzed Reactions ◽  
The Individual ◽  
Individual Rate ◽  
Catalyzed Oxidation

In this work, all the rate constants in the kinetic mechanism of the yeast alcohol dehydrogenase-catalyzed oxidation of ethanol by NAD+, at pH 7.0, 25 ?C, have been estimated. The determination of the individual rate constants was achieved by fitting the reaction progress curves to the experimental data, using the procedures of the FITSIM and KINSIM software package of Carl Frieden. This work is the first report in the literature showing the internal equilibrium constants for the isomerization of the enzyme-NAD+ complex in yeast alcohol dehydrogenase-catalyzed reactions.

Acid-catalyzed hydrolysis of 2-methylene-1,3-dithiolane. 2. Remarkable effects of β substitution on reversibility of the carbon protonation

1986 ◽  
Vol 64 (6) ◽  
pp. 1116-1123 ◽  
Author(s):  
Tadashi Okuyama ◽  
Masayoshi Toyoda ◽  
Takayuki Fueno
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Isotope Exchange ◽  
Relative Stabilities ◽  
The Third ◽  
Initial Carbon ◽  
Acid Catalyzed ◽  
The Individual ◽  
Individual Rate ◽  
Hydrolysis Of

Hydrolyses of 2-ethylidene-(1b), 2-isopropylidene-(1c), and 2-benzylidene-1,3-dithiolane (1d) were kinetically investigated in aqueous solution. All the individual rate constants involved in this three-step reaction were evaluated. Initial carbon protonation is only partially reversible (k2/k−1 = 1.33, 0.68, and 1.02 for 1b, 1c, and 1d, respectively) at higher pH, while the protonation becomes completely reversible below pH 2 where the third step is rate determining. Complete H–D isotope exchange at the β-carbon of 1b and 1d was observed in deuterium media before appreciable hydrolysis took place. It was demonstrated that reversion from the tetrahedral intermediate 3 to 1 occurs extensively during the reaction in the latter acidity range. Relative stabilities and reactivities of the olefinic substrates 1 are discussed.

The determination of the individual rate constants of polyethylene (PE) chlorination

1971 ◽  
Vol 13 (11) ◽  
pp. 2798-2805 ◽  
Author(s):  
L.B. Krentsel' ◽  
A.D. Litmanovich ◽  
I.V. Pastukhova ◽  
V.A. Agasandyan
Keyword(s):  
Rate Constants ◽  
The Individual ◽  
Individual Rate

scholarly journals Architecture of Allosteric Structure. Rate Equations, Rate Constants, and Equilibrium Constants for Reaction of: Hb4 with O2 and (HbO2)4 with Dithionate, in the Presence of 2,3-Bisphosphoglycerate

2019 ◽  
Author(s):  
Francis Knowles ◽  
Samantha J. Doyle ◽  
Douglas Magde
Keyword(s):  
Rate Constants ◽  
Binding Constant ◽  
Equilibrium Constants ◽  
Rate Equations ◽  
Rate Law ◽  
First Order ◽  
Equilibrium Binding ◽  
Binding Curve ◽  
O2 Binding

Three unknown quantities are all that is required to describe the O2-equilibrium binding curve for fractional saturation of human hemoglobin in red blood cells, under standard conditions: Kα, the O2-binding constant of equivalent α-chains; KC, the equilibrium constant for the T →R conformation change; Kβ, the O2-binding constant of equivalent β-chains. The model for formulation of the equation of state is a 3-stage ordered sequence of reactions. The values of were established by determination of rate constants for the oxygenation reaction and the dithionite-mediated de oxygenation reaction. The rate law for the forward reaction in the presence of excess O2 yields The same rate law yields for the dithionite-mediated de-oxygenation reaction. The rate constants for binding O2 are pseudo-first-order. The rate constants for release of O2 are first-order. Reactions involving O2, are 2-step ordered sequences of equivalent subunits. Progress curves for a 2-step ordered sequence of equivalent chains collapse to a first order reaction. Progress curves for both oxygenation and dithionite-mediated de-oxygenation reactions return is 0.0580 for the oxygenation reaction and 0.0358 for the dithionite-mediated de-oxygenation reaction. The corresponding values from the O2-equilibrium binding curve are: and = 0.02602. Values of determined from rate constants of progress curves for oxygenation and dithionite-mediated de-oxygenation reactions are close to values of determined by analysis of the O2-equilibrium binding curves for whole blood, by the Perutz/Adair equation.<br>

scholarly journals Architecture of Allosteric Structure. Rate Equations, Rate Constants, and Equilibrium Constants for Reaction of: Hb4 with O2 and (HbO2)4 with Dithionate, in the Presence of 2,3-Bisphosphoglycerate

2019 ◽  
Author(s):  
Francis Knowles ◽  
Samantha J. Doyle ◽  
Douglas Magde
Keyword(s):  
Rate Constants ◽  
Binding Constant ◽  
Equilibrium Constants ◽  
Rate Equations ◽  
Rate Law ◽  
First Order ◽  
Equilibrium Binding ◽  
Binding Curve ◽  
O2 Binding

Three unknown quantities are all that is required to describe the O2-equilibrium binding curve for fractional saturation of human hemoglobin in red blood cells, under standard conditions: Kα, the O2-binding constant of equivalent α-chains; KC, the equilibrium constant for the T →R conformation change; Kβ, the O2-binding constant of equivalent β-chains. The model for formulation of the equation of state is a 3-stage ordered sequence of reactions. The values of were established by determination of rate constants for the oxygenation reaction and the dithionite-mediated de oxygenation reaction. The rate law for the forward reaction in the presence of excess O2 yields The same rate law yields for the dithionite-mediated de-oxygenation reaction. The rate constants for binding O2 are pseudo-first-order. The rate constants for release of O2 are first-order. Reactions involving O2, are 2-step ordered sequences of equivalent subunits. Progress curves for a 2-step ordered sequence of equivalent chains collapse to a first order reaction. Progress curves for both oxygenation and dithionite-mediated de-oxygenation reactions return is 0.0580 for the oxygenation reaction and 0.0358 for the dithionite-mediated de-oxygenation reaction. The corresponding values from the O2-equilibrium binding curve are: and = 0.02602. Values of determined from rate constants of progress curves for oxygenation and dithionite-mediated de-oxygenation reactions are close to values of determined by analysis of the O2-equilibrium binding curves for whole blood, by the Perutz/Adair equation.<br>

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