Adenosine 5'-triphosphate synthesis driven by a protonmotive force in membrane vesicles of Escherichia coli

Abstract

Adenosine 5'-triphosphate (ATP) synthesis energized by an artificially imposed protonmotive force (delta p) in adenosine 5'-diphosphate-loaded membrane vesicles of Escherichia coli was investigated. The protonmotive force is composed of an artificially imposed pH gradient (delta pH) or membrane potential (deltapsi), or both. A delta pH was established by a rapid alteration of the pH of the assay medium. A delta psi was created by the establishment of diffusion potential of K+ in the presence of valinomycin. The maximal amount of ATP synthesized was 0.4 to 0.5 nmol/mg of membrane protein when energized by a delta pH and 0.2 to 0.3 nmol/mg of membrane protein when a delta psi was imposed. Simultaneous imposition of both a delta pH and delta psi resulted in the formation of greater amounts of ATP (0.8 nmol/mg of membrane protein) than with either alone. The amount of ATP synthesized was roughly proportional to the magnitude of the artificially imposed delta p. Although p-chloromercuribenzoate, 2-heptyl-4-hydroxyquinoline-N-oxide, or NaCN each inhibits oxidation of D-lactate, and thus oxidative phosphorylation, none inhibited ATP synthesis driven by an artificially imposed delta p. Membrane vesicles prepared from uncA or uncB strains, which are defective in oxidative phosphorylation, likewise were unable to catalyze ATP synthesis when energy was supplied by an artificially imposed delta p.