Influence of additional metal ions on the ratio of conversion rates of intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed by the Cu2+ ion: 1. Experimental study of the influence of Mg2+ ions in the ascending branch of the dependence of the initial hydrolysis rate on pH

The hydrolysis of the dimeric complex (CuATP2−)2 to CuADP− and inorganic phosphate Pi is irreversible. The main intermediate hydrolysis product, whose formation should be taken into account at relatively early steps of hydrolysis, is the pentacovalent intermediate IntK formed in parallel with the hydrolysis to CuADP− and Pi through the common intermediate product (CuATP2−)2OH− (DOH−) in step 1, which is the replacement of the nucleophile (OH−) at the Cu2+ ion by OH− at the positively charged phosphorus atom. The influence of the addition of Mg2+ ions is studied (depending on their concentration) on the rate constants of step 1 in the region of pH in the ascending branch of the dependence of the initial hydrolysis rate on pH at two values of pH: 6.48 and 6.70. This region of pH is sensitive to both the rate constant of DOH− formation and the rate constants of step 1. The rate constant for the formation of DOH− from D remains unchanged. An increase in the concentration of Mg2+ decreases the value of ATP conversion, above which the stationary hydrolysis regime is observed. The ratio [IntK]/[DOH−] is higher when the stationary regime is attained. The applicability of the method proposed for the formation of the attacking nucleophile and the proposed sequence of steps to the enzymatic phosphoryl transfer processes is discussed.