The electrochemical gradient of protons and its relationship to active transport in Escherichia coli membrane vesicles.

Abstract

Membrane vesicles isolated from E. coli generate a trans-membrane proton gradient of 2 pH units under appropriate conditions when assayed by flow dialysis. Using the distribution of weak acids to measure the proton gradient (.DELTA.pH) and the distribution of the lipophilic cation triphenylmethylphosphonium to measure the electrical potential across the membrane (.DELTA..PSI.), the vesicles are shown to generate an electrochemical proton gradient (.DELTA..hivin..mu.H+) of .apprx. -180 mV at pH 5.5 in the presence of ascorbate and phenazine methosulfate, the major component of which is a .DELTA.pH of .apprx. -110 mV. As external pH is increased, .DELTA.pH decreases, reaching 0 at pH .gtoreq. 7.5, while .DELTA..PSI. remains .apprx. -75 mV and internal pH remains at pH 7.5. The ability of various electron donors to drive transport is correlated with their ability to generate .DELTA..hivin..mu.H+. .DELTA.pH and .DELTA..PSI. can be varied reciprocally in the presence of valinomycin and nigericin. The role of chemiosmotic phenomena in active transport is strongly indicated.