title: Electrochemical proton gradient in Micrococcus lysodeikticus cells and membrane vesicles.
abstract: Using the distribution of weak acids to measure the pH gradient (delta pH; interior alkaline) and the distribution of the lipophilic cation [3H]tetraphenylphosphonium+ to monitor the membrane potential (delta psi; interior negative), we studied the electrochemical gradient or protons (delta mu- H+) across the membrane of Micrococcus lysodeikticus cells and plasma membrane vesicles. With reduced phenazine methosulfate as electron donor, intact cells exhibited a relatively constant delta mu- H+ (interior negative and alkaline) of -193 mV to -223 mV from pH 5.5 to pH 8.5. On the other hand, in membrane vesicles under the same conditions, delta mu- H+ decreased from a maximum value of -166 mV at pH 5.5 to -107 mV at pH 8.0 and above. This difference is related to a differential effect of external pH on the components of delta mu- H+. In intact cells, delta pH decreased from about -86 mV (i.e., 1.4 units) at pH 5.5 to zero at pH 7.8 and above, and the decreases in delta pH was accompanied by a reciprocal increase in delta psi from -110 mV at pH 5.5 to -211 mV at pH 8.0 and above. In membrane vesicles, the decrease in delta pH with increasing external pH was similar to that described for intact cells; however, delta psi increased from -82 mV at pH 5.5 to only -107 mV at pH 8.0 and above.
mesh_terms: D001565:Benzoates / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003956:Dialysis; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D008744:Methylamines / Q000378:metabolism; D008773:Methylphenazonium Methosulfate / Q000378:metabolism; D008837:Micrococcus / Q000378:metabolism*; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D001565:Benzoates; D008744:Methylamines; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D014634:Valinomycin; D008773:Methylphenazonium Methosulfate; C013289:tetraphenylphosphonium