ATP synthase complex from bovine heart mitochondria. Passive H+ conduction through mitochondrial coupling factor 6-depleted F0 complexes.

Submitochondrial particles prepared by treatment of mitochondria with ammonia and silicotungstic acid were found to be deficient in coupling factor 6 according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting and had reduced ATP-Pi exchange activity. Requirement of coupling factor 6 for passive proton conductance through mitochondrial F0 was investigated by assaying the ability of depleted particles to sustain NADH-induced proton fluxes as measured by the quenching of 9-amino-6-chloro-2-methoxyacridine fluorescence. The depleted particles themselves showed negligible quenching, but the quenching increased markedly after treating the particles with oligomycin. The data show for the first time that coupling factor 6-depleted complexes have an active proton channel that can be blocked by oligomycin. Therefore, coupling factor 6 is not essential for inhibitor-sensitive proton conductance through mitochondrial F0.