Control of phosphoenolpyruvate-dependent phosphotransferase-mediated sugar transport in Escherichia coli by energization of the cell membrane.

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Abstract
The phosphoenolpyruvate-dependent phosphotransferase-mediated sugar transport in E. coli is inhibited by the energized state of the membrane. This was shown in intact cells and in membrane vesicles. Relaxation of the proton gradient by uncouplers stimulated the uptake of sugars via the phosphotransferase system in aerobically cultured cells. No such effect was seen in anaerobic cells, apparently because the cell membrane of these cells is poorly energized. Energization by respiration of D-lactate or ascorbate inhibited the phosphotransferase uptake system in membrane vesicles. This inhibition was reversed by the addition of cyanide. Oxamate, a specific inhibitor of lactate dehydrogenase, prevented the inhibitory effect of D-lactate. Membrane vesicles prepared from a cytochrome-less mutant were not energized by D-lactate oxidation and the phosphotransferase uptake system was not inhibited.