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

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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 +.