Mathematical modelling of kinetics of adenosine 5 '-triphosphate hydrolysis catalyzed by Zn2+ ion in the pH range 7.1-7.4

摘要

Kinetic data on hydrolysis of ZnATP(2-) complexes confirm the enzyme-like mechanism of the reaction. The whole sequence of steps for the formation and transformations of the intermediates is established by numerical modelling in a wide range of concentrations (4X10(-4)-0.3 M) in the pH range 7.1-7.4. The rates of active center formation and appropriate equilibria are governed by H+ transfer from coordinated water with formation of hydrogen bond between the (N1) atom of the second ZnATP(2-) molecule and the gamma -phosphate moiety of the first ZnATP(2-) molecule. The rate and equilibrium constants are higher in trimeric associates as compared to dimeric ones. Among the steps of ADP formation in the pH-independent channel, H+ transfer from the hydrogen bond with O--P-gamma of ZnATP(2-) to the hydrogen bond with O--P-beta of ZnADP(-) forming in the course of general base catalysis is the rate determining step. It is followed by the rapid and reversible substitution of ligand H2PO4- by H2O in the Zn2+ coordination sphere. Hydrogen bond participation leads to reversible ADP formation. AMP is shown to be formed also via associates, and the conformation transformation determines the induction period. The induction period decreases as the concentration of ZnATP(2-) increases. The rate and equilibrium constants of all steps are evaluated and variation of the intermediate concentrations in the course of hydrolysis is presented. (C) 2000 Elsevier Science S.A. All rights reserved. [References: 52]