Mechanisms of Active Transport in Isolated Membrane Vesicles

Abstract

Abstract An artificial electron donor system—ascorbate and phenazine methosulfate—markedly stimulates β-galactoside transport in isolated membrane vesicles from Escherichia coli ML 308-225. Maximal rates of transport are dependent on the presence of both ascorbate and phenazine methosulfate and also oxygen. Moreover, in the presence of phenazine methosulfate, reduced nicotinamide adenine dinucleotide stimulates the initial rate of lactose transport. The effect of ascorbate-phenazine methosulfate is inhibited by removal of oxygen or potassium cyanide, 2-heptyl-4-hydroxyquinoline-N-oxide, p-chloromercuribenzoate, or sodium amytal. Oxamic acid has no significant effect. Ascorbate-phenazine methosulfate reduces the respiratory chain of the vesicles below the potential level of cytochrome b1, but above approximately 80% of the membrane-bound flavoproteins. In the presence of ascorbate-phenazine methosulfate, membranes prepared from Escherichia coli, Salmonella typhimurium, Pseudomonas putida, Proteus mirabilis, Bacillus megaterium, and Bacillus subtilis catalyze the concentrative uptake of proline; membranes prepared from Staphylococcus aureus catalyze the concentrative uptake of lysine; and membranes prepared from Micrococcus dentrificans catalyze the concentrative uptake of glutamine.