The Non‐catalytic Nucleotide‐Binding Site of Mitochondrial ATPase Is Localised on the α‐Subunit(s)of Factor F₁

Abstract

The incubation of isolated factor F 1 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 F 1 is not accompanied by any changes in the ATPase activity of the enzyme. The modification of factor F 1 is preceded by the reversible binding of oxADP with the enzyme with a K d of 80 μM. ADP partly prevents factor F 1 from modification by oxADP. The electrophoresis of modified factor F 1 in polyacrylamide gel in the presence of sodium dodecyl sulphate showed that oxADP binds with the α‐subunit(s) of factor F 1 . When submitochondrial particles are incubated with [ 3 H]oxADP, the main part of the radioactive label may be discovered in the polypeptide with a molecular weight of some 30000 which is probably the adenine nucleotides' translocase. The isolation of factor F 1 from particles preincubated with [ 3 H]oxADP showed that the membrane‐bound factor F 1 covalently binds 0.2–0.3 mol of oxADP per mol of enzyme. Here again, all the oxADP is bound with the α‐subunit(s) of factor F 1 . The modification of membrane‐bound factor F 1 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 ATPase located on the α‐subunit(s) of factor F 1 may participate in the mechanism of ATP hydrolysis by membrane‐bound ATPase.