Effect of additional metal ions on the ratio between the rates of the transformation of the intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed the Cu2+ ion (Communication 2: Mathematical modeling of the kinetics of the hydrolysis in the presence of additional Mg2+ ions)

Abstract

It was previously shown that the hydrolysis of the (CuATP2− · OH2)2 dimeric complex to CuADP− and an inorganic phosphate occurs in a sequence of two rapid and irreversible steps. Along with the hydrolysis through a common intermediate product, (CuATP2−)2OH−-(DOH−), the OH− nucleophile at the Cu2+ ion is replaced by OH− at the positively charged phosphorus atom to form an IntK pentacovalent intermediate (step 1). A mathematical modeling of the kinetics of the hydrolysis catalyzed by the Cu2+ base metal ion in the presence of additional Mg2+ ions at two pH values, 6.48 and 6.71 (at the ascending branch of the dependence of the initial rate of the hydrolysis on the pH value) is performed. Additional ions affect only the pathway of coupling of the conformational conversion of DOH−. The rate constant for the forward reaction (IntK→ DOH−), k 1, increases from 2 · 107 L mol−1 min−1 in the absence of Mg2+ to 2.9 · 107 L mol−1 min−1 upon introduction of Mg2+ ions; rate constant of the reverse reaction IntK → DOH→, k −1, decreases from 1 · 105 L mol−1 min−1 in the absence of Mg2+ to 3 · 104 L mol−1 min−1 in the presence of Mg2+. The relative concentrations of the intermediate products are demonstrated to change during the irreversible hydrolysis. In the presence of Mg2+, IntK emerges at much earlier stages of the hydrolysis, the fraction of formed IntK in the balance of NuP0 is substantially higher, and the growth of its relative concentration with time in the earlier stages of hydrolysis is much more dramatic.