ACTIVE-K+ TRANSPORT IN MYCOPLASMA-MYCOIDES VAR CAPRI - RELATIONSHIPS BETWEEN K+-DISTRIBUTION, ELECTRICAL POTENTIAL AND ATPASE ACTIVITY

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, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, dissipate the K+ concentration gradient only when combined with valinomycin. Variations in the merocyanine fluorescence intensity indicate that a transmembrane electrical potential (Δψ) is generated on cell energization. This Δψ, 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 controls K+ distribution in these organisms through the generation of a transmembrane electrical potential difference. © 1979.