Effect of the proton electrochemical gradient on maleimide inactivation of active transport in Escherichia coli membrane vesicles

Abstract

Many active transport systems present in E. coli membrane vesicles are inhibited by maleimides and other sulfhydryl reagents. These reagents do not interfere with the oxidation of reduced phenazine methosulfate or with the electrochemical proton gradient (.DELTA..hivin..mu.H+). The rate of inactivation of the .beta.-galactoside transport system by various maleimides is increased in the presence of reduced phenazine methosulfate, and it is shown that the electrochemical proton gradient is responsible for the effect. Similar effects are observed with the proline and melibiose transport systems. It appears that either the reactivity or accessibility of a sulfhydryl group(s) in each of these carriers is altered by the presence of a transmembrane .DELTA..hivin..mu.H+. The findings are consistent with the notion that .DELTA..hivin..mu.H+, in addition to acting as the immediate driving force for active transport, may bring about structural or conformational changes in certain membrane proteins that catalyze active transport.