ATP synthesis catalyzed by the mitochondrial F₁‐F₀ ATP synthase is not a reversal of its ATPase activity

The ADP(Mg²⁺)-deactivated oligomycin-sensitive F₁-F₀ ATPase of coupled submitochondrial particles treated with the substoichiometric amount of oligomycin was studied to test whether ATP synthesis and hydrolysis proceed in either direction through the same intermediates. The initial rates of ATP hydrolysis, oxidative phosphorylation, ATP-dependent, succinate-supported NAD⁺ reduction, and ATP-induced generation were measured using deactivated ATPase trapped by azide [Biochem. J. (1982) 202, 15–23]. Three ATP consuming reactions were strongly inhibited when azide was present in the assay mixtures, whereas ATP synthesis was not altered by azide. The unidirectional effect of azide is not consistent with three alternating binding sites mechanism operating in ATP synthesis and support our hypothesis on the existence of nucleotide(Mg²⁺)-controlled ‘synthase’ and ‘hydrolase’ states of the mitochondrial F₁-F₀ ATPase.