Competition between Two Pathways for Sugar Uptake by the Phosphoenolpyruvate‐Dependent Sugar Phosphotransferase System in Salmonella typhimurium

Abstract

The interaction between the 2 pathways for glucose entry via the phosphoenolpyruvate:sugar phosphotransferase system, i.e., via enzyme II-A/II-B and enzymes II-BGlc, was studied in S. typhimurium. Thio-.beta.-D-glucoside and 5-thio-D-glucose were substrates of P-pyruvate:sugar phosphotransferase specific for enzyme II-BGlc both in intact cells and in toluene-treated cells of S. typhimurium. The activity of the II-A II-B pathway was strongly inhibited by the presence of II-BGlc substrates. The 2 pathways thus compete for phosphoryl groups provided by P-pyruvate. Under the conditions tested, the flow of phosphoryl groups through enzyme I/HPr is the rate-limiting step in vivo of activity of the pathways flow of phosphoryl groups through enzyme I/HPr is the rate-limiting step in vivo of activity of the pathways studied. The proposed mechanism of the regulatory function of the P-pyruvate:sugar phosphotransferase system which predicts a net dephosphorylation of components of the P-pyruvate:sugar phosphotransferase in the spresence of a substrate of P-pyruvate:sugar phosphotransferase is corroborated.