Active K+ transport in Mycoplasms mycoides var. Capri. Relationships between K+ distribution, electrical potential...

The addition of 5 . 10(-5) M or less of dicyclohexylcarbodiimide to Mycoplasma mycoides var. Capri preferentially influences K+ influx rather than efflux and reduces by 30--40% the activity of the membrane-bound Mg2+- ATPase. Adding valinomycin to metabolizing cells does not markedly affect K+ distribution but induces a rapid and complete loss of intracellular K+ in non-metabolizing cells. Uncoupling agents such as dinitrophenol, carbonylcyanide p-trifluoromethoxyphenylhydrazone, dissipate the K+ concentration gradient only when combined with valinomycin. Variations in the merocyanine fluorescence intensity indicate that a transmembrane electrical potential (delta psi) is generated on cell energization. This delta psi, not affected by valinomycin or uncouplers when used alone, is collapsed by a mixture of both. No change in fluorescence intensity can be detected when glucose is added to dicyclohexylcarbodiimide treated organisms. These experiments suggest that the membrane-bound Mg-ATPase activity control K+ distribution in these organisms through the generation of a transmembrane electrical potential difference.