Energization of the membrane prevents the formation of tight inactive complexes of ATPase with MgADP in submitochondrial particles

Abstract

Mitochondrial ATPase binds ADP tightly, forming inactive complexes. Dissociation of the complexes is blocked by azide. Azide inhibits neither ATP hydrolysis at high δ μ H + nor ATP-dependent NAD + reduction, provided that the ADP concentration is higher than 10 −4 M. At lower ADP levels, azide is inhibitory. These data suggest that in the presence of ATP δ μ H + prevents the fromation of one of the inactive complexes. In the absence of ATP at high δ μ H +, azide-sensitive complexes are not formed at any ADP concentrations tested (5 × 10 −7-5 × 10 −4 M). The inactive E·ADP complexes can play a significant role in the regulation of ATPase in mitochondria, preventing futile ATP hydrolysis at low δ μ H +.