ATP synthesis by the F1Fo ATP synthase of Escherichia coli is obligatorily dependent on the electric potential.

The H+-translocating F1Fo ATP synthase of Escherichia coli was purified and reconstituted into proteoliposomes. This system catalyzed ATP synthesis when energized by an acid/base transition (pHin = 5.0; pHout = 8.3) with succinate, malonate or maleinate but not with MES as the acidic buffer. Under these experimental conditions an electric potential of 125-130 mV is generated by the diffusion of succinate, probably the monoanionic species, whereas with MES buffer the measured potential was at background level (approximately 5 mV). ATP was also synthesized at pH 7.2 in the absence of a delta pH by applying a K+/valinomycin diffusion potential. The rate of ATP synthesis increased with the potential in an exponential manner with an inflection point at about 70 mV. We conclude from these results that delta pH and delta psi are kinetically unequivalent driving forces for ATP synthesis by the E. coli ATP synthase and that delta psi is a mandatory force for this synthesis. The significance of these findings for the mechanism of ATP synthesis in general is discussed.