Rotation of the c subunit oligomer in fully functional F1Fo ATP synthase

The F 1 F o -type ATP synthase is the smallest motor enzyme known. Previous studies had established that the central γ and ɛ subunits of the F 1 part rotate relative to a stator of α 3 β 3 and δ subunits during catalysis. We now show that the ring of c subunits in the F o part moves along with the γ and ɛ subunits. This was demonstrated by linking the three rotor subunits with disulfide bridges between cysteine residues introduced genetically at the interfaces between the γ, ɛ, and c subunits. Essentially complete cross-linking of the γ, ɛ, and c subunits was achieved by using CuCl 2 to induce oxidation. This fixing of the three subunits together had no significant effect on ATP hydrolysis, proton translocation, or ATP synthesis, and each of these functions retained inhibitor sensitivity. These results unequivocally place the c subunit oligomer in the rotor part of this molecular machine.