Transmembrane proton-motive potential of Spiroplasma floricola

In Spiroplasma floricola, the transmembrane proton-motive potential delta p was studied. It is composed of a transmembrane electric potential difference, delta psi, and a transmembrane proton gradient, delta pH, according to delta p = delta psi - (Z.delta pH). Using a potential-sensitive carbocyanine dye and 5,5'-dimethyl[2-14C]oxazolidine-2,4-dione as probes, delta psi and delta pH were measured at different [H+] of the medium, and delta p was calculated to be remarkably constant at -123 mV +/- 16% over a wide range of external pH values. Inhibition experiments indicated that it is generated by a membrane-bound, electrogenic, proton-translocating ATPase.