Energy-dependent transformation of the catalytic activities of the mitochondrial F0·F1-ATP synthase

AbstractThe ADP(Mg2+)-deactivated, azide-trapped F0·F1-ATPase of coupled submitochondrial particles is capable of ATP synthesis being incapable of ATP hydrolysis and ATP-dependent Δμ̄H+ generation [FEBS Lett. (1995) 366, 29–32]. This puzzling phenomenon was studied further. No ATPase activity of the submitochondrial particles catalyzing succinate-supported oxidative phosphorylation in the presence of azide was observed when ATP was added to the assay mixture after an uncoupler. Rapid ATP hydrolysis was detected in the same system when ATP followed by an uncoupler was added. Less than 5% of the original ATPase activity was seen when the reaction (assayed with ATP-regenerating system) was initiated by the addition of ATP to the azide-trapped coupled particles oxidizing succinate either in the presence or in the absence of the uncoupler. High ATP hydrolytic activity was revealed when the reaction was started by the simultaneous addition of the ATP plus uncoupler to the particles generating Δμ̄H+. The energy-dependent conversion of the enzyme into latent uncoupler-activated ATPase was prevented by free ADP (Ki≈20 μM) and was greatly enhanced after multiple turnovers in oxidative phosphorylation. The results suggest that the catalytic properties of F0·F1 are Δμ̄H+-dependent which is in accord with our hypothesis on different conformational states of the enzyme participating in ATP synthesis or hydrolysis