Mechanisms of Active Transport in Isolated Bacterial Membrane Vesicles

Valinomycin-induced uptake of rubidium by membrane vesicles prepared from Escherichia coli, Staphylococcus QUreus, and Micrococcus denifrificans is analogous in nearly all respects to the transport of sugars or amino acids, or both, by these membrane vesicles. In E. coli membrane vesicles, concentrative rubidium uptake is stimulated maximally by D-lactate and by the artificial electron donor ascorbate-phenazine methosulfate, to a lesser extent by L-lactate, DL-a-hydroxybutyrate, succinate, and reduced diphosphopyridine nucleotide, and not at all by ATP, phosphoenolpyruvate, or a number of other metabolites. There is no direct relationship between the ability of various electron donors to stimulate rubidium uptake (ascorbate-phenazine methosulfate >> D-lactate >> L-lactate > DL-a-hydroxybutyrate > succinate > reduced diphosphopyridine nucleotide) and their rates of oxidation by membrane vesicles (ascorbate-phenazine methosulfate >> reduced diphosphopyridine nucleotide > succinate > D-lactate > Llactate > DL-a-hydroxybutyrate). In the presence of Dlactate and valinomycin, the initial rate of rubidium uptake versus the rate of D-lactate oxidation yields a ratio of nearly