CONTROL OF GLUCOSE-METABOLISM BY THE ENZYMES OF THE GLUCOSE PHOSPHOTRANSFERASE SYSTEM IN SALMONELLA-TYPHIMURIUM

The quantitative role of the phosphoenolpyruvate:glucose phosphotransf erase system (glucose phosphotransferase system) in glucose uptake and metabolism, and phosphotransferase-system-mediated regulation of glyc erol uptake, was studied in vivo in Salmonella typhimurium. Expression plasmids were constructed which contained the genes encoding enzyme I (ptsI), HPr (ptsH), IIA(Glc) (crr), and IICBGlc (ptsG) of the glucose phosphotransferase system behind inducible promoters. These plasmids allowed the controlled expression of each of the glucose phosphotransf erase system proteins from about 30% to about 300% of its wild-type le vel. When enzyme I, HPr or IIA(Glc) were modulated between 30% and 300 % of their wild-type value, hardly any effects on the growth rate on g lucose, the glucose oxidation rate, the rate of methyl alpha-D-glucopy ranoside (a glucose analog) uptake or the phosphotransferase-system-me diated inhibition of glycerol uptake by methyl alpha-D-glucopyranoside were observed. Employing the method of metabolic control analysis, it was shown that the enzyme flux control coefficients of these phosphot ransferase system components on the different measured processes were close to zero. The enzyme flux control coefficient of IICBGlc on growt h on glucose or glucose oxidation was also close to zero. In contrast, the enzyme flux control coefficient of IICBGlc on the flux through th e glucose phosphotransferase system (transport and phosphorylation) wa s 0.72. The experimentally determined enzyme flux control coefficients allowed us to calculate the flux control coefficients of the phosphoe nolpyruvate/pyruvate and methyl alpha-D-glucopyranoside/methyl alpha-D -glucopyranoside 6-phosphate couples and the process control coefficie nts of the phosphotransfer reactions of the glucose phosphotransferase system. We discuss the implications of these values and the possible control points in the glucose phosphotransferase system.