Proton-powered subunit rotation in single membrane-bound F0F1-ATP synthase

Synthesis of ATP from ADP and phosphate, catalyzed by F0F1-ATP synthases, is the most abundant physiological reaction in almost any cell. F0F1-ATP synthases are membrane-bound enzymes that use the energy derived from an electrochemical proton gradient for ATP formation. We incorporated double-labeled F0F1-ATP synthases from Escherichia coli into liposomes and measured single-molecule fluorescence resonance energy transfer (FRET) during ATP synthesis and hydrolysis. The γ subunit rotates stepwise during proton transport–powered ATP synthesis, showing three distinct distances to the b subunits in repeating sequences. The average durations of these steps correspond to catalytic turnover times upon ATP synthesis as well as ATP hydrolysis. The direction of rotation during ATP synthesis is opposite to that of ATP hydrolysis.