Dodecamer rotor ring defines H+/ATP ratio for ATP synthesis of prokaryotic V-ATPase from Thermus thermophilus

ATP synthesis by V-ATPase from the thermophilic bacterium Thermus thermophilus driven by the acid-base transition was investigated. The rate of ATP synthesis increased in parallel with the increase in proton motive force (PMF) >110 mV which is composed of a difference in proton concentration (Delta pH) and the electrical potential differences (Delta Psi) across membranes. The optimum rate of synthesis reached 85 s(-1), and the H+/ATP ratio of 4.0 +/- 0.1 was obtained. ATP was synthesized at a considerable rate solely by Delta pH, indicating Delta Psi was not absolutely required for synthesis. Consistent with the H+/ATP ratio, cryoelectron micrograph images of 2D crystals of the membrane-bound rotor ring of the V-ATPase at 7.0-angstrom resolution showed the presence of 12 V-o-c subunits, each composed of two transmembrane helices. These results indicate that symmetry mismatch between the rotor and catalytic domains is not obligatory for rotary ATPases/synthases.