Control of glucose metabolism by enzyme IIGlc of the phosphoenolpyruvate-dependent phosphotransferase system in Escherichia coli

Abstract

The quantitative effects of variations in the amount of enzyme IIGlc of the phosphoenolpyruvate:glucose phosphotransferase system (PTS) on glucose metabolism in Escherichia coli were studied. The level of enzyme IIGlc could be adjusted in vivo to between 20 and 600% of the wild-type chromosomal level by using the expression vector pTSG11. On this plasmid, expression of the structural gene for enzyme IIGlc, ptsG, is controlled by the tac promoter. As expected, the control coefficient (i.e., the relative increase in pathway flux, divided by the relative increase in amount of enzyme) of enzyme IIGlc decreased in magnitude if a more extensive pathway was considered. Thus, at the wild-type level of enzyme IIGlc activity, the control coefficient of this enzyme on the growth rate on glucose and on the rate of glucose oxidation was low, while the control coefficient on uptake and phosphorylation of methyl alpha-glucopyranoside (an enzyme IIGlc-specific, nonmetabolizable glucose analog) was relatively high (0.55 to 0.65). The implications of our findings for PTS-mediated regulation, i.e., inhibition of growth on non-PTS compounds by glucose, are discussed.