Transport of Sugars and Amino Acids in BacteriaXI. Mechanism of Energy Coupling Reaction for the Concentrative Uptake of Proline by Escherichia coli Membrane Vesicles*

Abstract

The membrane vesicles prepared from Escherichia coli W3092 could take up proline against a concentration gradient in the presence of succinate or D-(−)-lactate as energy source. The transport carrier of the membrane vesicles remained active and was found to be specific for proline. Zinc ions strongly inhibited the uptake reaction initiated by succinate, the ID₅₀ value being 15 μM. The inhibition by zinc ions was non-competitive. The K⁺-loaded membrane vesicles also took up proline against a concentration gradient when valinomycin was added to the reaction system. The valinomycin-induced uptake of proline was not inhibited by zinc ions. Mercury ions inhibited strongly both succinate-driven and valinomycin-induced uptakes of proline by the membrane vesicles. Evidence strongly suggests that energy coupled with the concentrative uptake of proline by the membrane vesicles is a membrane potential and that zinc ions inhibit the generation of a membrane potential by blocking oxidation of succinate.