Embedded in the membrane, a ring of 10 c-subunits (in the E. coli enzyme) rotates during proton transport. The proton entrance and exit channels are probably located in the a-subunit (the non-rotating counterpart together with the b-subunits of F_o).

Proton uptake and release at the a- and c-subunit interface might involve transmembrane helix rotation (‘swivelling mechanism’).