LIMITS TO INDUCER EXCLUSION - INHIBITION OF THE BACTERIAL PHOSPHOTRANSFERASE SYSTEM BY GLYCEROL KINASE

The uptake of methyl alpha-D-glucopyranoside by the phosphoenolpyruvat e-dependent phosphotransferase system of Salmonella typhimurium could be inhibited by prior incubation of the cells with glycerol. Inhibitio n was only observed for glycero preincubation times longer than 45s an d required the preinduction of both the glucose and the glycerol-catab olizing systems. Larger extents of inhibition by glycerol correlated w ith higher intracellular levels of glycerol kinase when the glp regulo n had been induced to different extents. Preincubation with lactate di d not inhibit methyl alpha-D-glucopyranoside uptake significantly, alt hough both lactate and glycerol were oxidized by the cells. The cellul ar free-energy state of the cells (intracellular [ATP]/[ADP] ratio) wa s virtually identical for lactate and glycerol preincubation, suggesti ng that the inhibition of phosphotransferase-mediated uptake was not a metabolic effect, In vitro, phosphotransferase activity was inhibited to a maximal extent of 32% upon titrating cell-free extracts with hig h concentrations of commercial glycerol kinase. The results show that uptake systems that have hitherto been regarded merely as targets of t he phosphotransferase system component IIA(Glc) also have the capacity themselves to retroinhibit the phosphotransferase system flux, presum ably by sequestration of the available IIA(Glc) provided that these sy stems are induced to appropriate levels.