The non-catalytic nucleotide-binding site of mitochondrial ATPase is localised on the alpha-subunit(s) of factor F1.

The incubation of isolated factor F1 with the di-aldehyde derivative of ADP (oxADP) which is formed as a result of ADP treatment by periodate, causes the covalent binding of 0.9--1 molecules of the oxADP with a molecule of the enzyme. This modification of factor F1 is not accompanied by any changes in the ATPase activity of the enzyme. The modification of factor F1 is preceded by the reversible binding of oxADP with the enzyme with a Kd of 80 micro M. ADP partly prevents factor F1 from modification by oxADP. The electrophoresis of modified factor F1 in polyacrylamide gel in the presence of sodium dodecyl sulphate showed that oxADP binds with the alpha-subunit(s) of factor F1. When submitochondrial particles are incubated with [3H]oxADP, the main part of the radioactive label may be discovered in the polypeptide with a molecular weight of some 30 000 which is probably the adenine nucleotides' translocase. The isolation of factor F1 from particles preincubated with [3H]oxADP showed that the membrane-bound factor F1 covalently binds 0.2--0.3 mol of oxADP per mol of enzyme. Here again, all the oxADP is bound with the alpha subunit(s) of factor F1. The modification of membrane-bound factor F1 by oxADP is accompanied by the partial inhibition of the particles' ATPase activity. The results obtained testify to the fact that the non-catalytic site of mitochondrial ATP ase located on the alpha-subunit(s) of factor F1 may participate in the mechanism of ATP hydrolysis by membrane-bound ATPase.