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

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Abstract
The interaction between the two pathways for glucose entry via the phosphoenolpyruvate: sugar phosphotransferase system, i.e. via enzyme II‐A/II‐B and enzymes II‐BGlc/IIIGlc, was studied in Salmonella typhimurium. Thio‐β‐d‐glucoside and 5‐thio‐d‐glucose were shown to be 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. It is concluded that the two pathways compete for phosphoryl groups provided by P‐pyruvate, and that 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 studied. The results corroborate 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 presence of a substrate of P‐pyruvate : sugar phosphotransferase.