Kinetics and mechanism of adenosine 5′-triphosphate hydrolysis catalyzed by the Cu2+ ion: The role of conformation and the catalytic effect of the OH− ion

Abstract

The kinetics of 5′-ATP hydrolysis catalyzed by the Cu2+ ion has been investigated by HPLC in the pH range 5.6–7.8 at 25°C. Two series of experiments differing in the initial [Cu · ATP]0 (1: 1) concentration have been carried out. The reaction was being conducted up to ≈40% ATP conversion. The (CuATP2−)2OH−⨑ub;DOH−⫂ub; complex, which consists of two monomeric Cy(CuATP2−) molecules (in which the N7 atom and the γ-phosphate group are coordinated to Cu2+), is responsible for the formation of CuADP− + Pi (Pi is an inorganic phosphate). The highest possible DOH− concentration at a given pH is reached at the initial stage of hydrolysis. The pH value at which the highest initial rate of ADP formation is reached (pHmax (w 0, ADP)) decreases as the D concentration increases. At pH > pHmax, the decrease in the ADP formation rate in the course of the processes is pH-independent and, once an ATP conversion of 20–26% is reached, hydrolysis proceeds in a steady-state regime such that ADP and AMP form from ATP by parallel reactions. The participation of the OH− ion in the catalysis of the formation of hydrolysis intermediates is considered.