[The Efficiency of ATP Synthase As a Molecular Machine]

On the basis of the experimentally measured isotope effect of magnesium (25)Mg on the rate of ATP synthesis by mithochondrial ATP synthase, the rate constants of the reactions in the catalytic site have been estimated. The limiting step of the synthesis is shown to be the addition of8phosphoryl anion-radical of ADP to the P=O bond of phosphate with the rate constant of 1,2 x 10(8) s(-1). From the ratio of the rate constants, the mechanochemical efficiency of ATP synthase was estimated to be about 10% for enzymes with (24, 26)Mg isotopes and to be doubled for enzymes with (25)Mg in the catalytic site.