Effect of pH and Metal Ion Concentration on the Equilibrium Hydrolysis of Adenosine Triphosphate to Adenosine Diphosphate

Abstract The observed equilibrium constant for the hydrolysis of ATP to ADP and inorganic phosphate has been calculated as a function of pH and pMg (-log (Mg2+)) at 25°, along with the numbers of moles of H+ and Mg2+ produced per mole of ATP hydrolyzed. This equilibrium constant has also been calculated as a function of pMg and pCa (-log (Ca2+)) at a constant pH of 7.4, along with the numbers of moles of Mg2+ and Ca2+ produced per mole of ATP hydrolyzed. The productions of inorganic phosphate, H+, Mg2+, and Ca2+ are linked through the acid dissociations and metal ion binding of ATP, ADP, and inorganic phosphate. Recalculation of earlier chemical equilibrium data has led to ΔG0'298 = -9500 cal mole-1 in the absence of magnesium ions, -8600 cal mole-1 at pMg = 2, and -8800 cal mole-1 at pMg = 3, at 25°, pH 7, and 0.2 ionic strength for the hydrolysis of ATP to ADP and inorganic phosphate. In limiting cases, the inkage may be seen to result from certain simple reactions.