QUANTIFICATION OF THE REGULATION OF GLYCEROL AND MALTOSE METABOLISM BY IIA(GLC) OF THE PHOSPHOENOLPYRUVATE-DEPENDENT GLUCOSE PHOSPHOTRANSFERASE SYSTEM IN SALMONELLA-TYPHIMURIUM

The amount of IIA(Glc), one of the proteins of the phosphoenolpyruvate:glucose phosphotransferase system (PTS), was modulated over a broad range with the help of inducible expression plasmids in Salmonella typhimurium. The in vivo effects of different levels of IIA(Glc) on glycerol and maltose metabolism were studied. The inhibition of glycerol uptake, by the addition of a PTS sugar, was sigmoidally related to the amount of IIA(Glc). For complete inhibition of glycerol uptake, a minimal ratio of about 3.6 mol of IIA(Glc) to 1 mol of glycerol kinase (tetramer) was required. Varying the level of IIA(Glc) (from 0 to 1,000% of the wild-type level) did not affect the growth rate on glycerol, the rate of glycerol uptake, or the synthesis of glycerol kinase. In contrast, the growth rate on maltose, the rate of maltose uptake, and the synthesis of the maltose binding protein increased two- to fivefold with increasing levels of IIA(Glc). In the presence of cyclic AMP, the maximal levels were obtained at all IIA(Glc) concentrations. The synthesis of the MalK protein, the target of IIA(Glc), was not affected by varying the levels of IIA(Glc). The inhibition of maltose uptake was sigmoidally related to the amount of IIA(Glc). For complete inhibition of maltose uptake by a PTS sugar, a ratio of about 18 mol of IIA(Glc) to 1 mol of MalK protein (taken as a dimer) was required.