Regulation of the glucose phosphotransferase system in Brochothrix thermosphacta by membrane energization

Uptake of 2-deoxyglucose, alpha-methylglucopyranoside, and glucose into intact cells of Brochothrix thermosphacta (formerly Microbacterium thermosphactum, ATCC 11509) was stimulated by KCN or CCCP. The glucose analogs were recovered almost totally as the sugar phosphates. Membrane vesicles were isolated from protoplasts and shown to be right side out by freeze fracturing and by using ATPase as a marker for the cytoplasmic membrane surface. Uptake of glucose into vesicles was dependent on the presence of phosphoenolpyruvate. NADH oxidation, K+ -diffusion gradients, and externally directed lactate gradients (pH greater than 7 initially) were used to generate transmembrane potentials across membrane vesicles. Above a threshold value of about -50 mV, uptake of glucose into membrane vesicles was reduced. Likewise, the maximum uptake of glucose and its two analogs into cells occurred when the protonmotive force was less than about -50 mV.