Simulation of dephosphorylation curves by an ensemble of enzyme molecules with different rate constants

Dear Sir, More than twenty years ago the Albers-Post scheme was proposed to describe the effects of ATP, ADP, Na, and K on transphosphorylation reactions carried out by Na, K-ATPase preparations. The scheme in its currently amplified version has been remarkably successful in accounting for the results of ion transport and transphosphorylation measurements, of physical and biochemical studies of the changes in pump configuration during transport cycles, of measurements of electrical events occurring during ion transport, and of measurements of the occlusion of Na and Rb ions by Na,K-ATPase preparations (Glynn, 1985, 1988). Basically, the Albers-Post scheme postulates that Na promotes phosphorylation of the pump by ATP to form the phosphorylated intermediate E1P, that Na is released during the conformational transition from EIP to E~P, that K promotes the dephosphorylation of E2P, and that K is released during the conformational transition from E 2 to El: