The phospho enol pyruvate: glucose phosphotransferase system of Salmonella typhimurium

Enzyme III Glc of the phospho enol pyruvate: sugar phosphotransferase system (PTS) of Salmonella typhimurium can occur in two forms: phosphorylated and nonphosphorylated. Phosphorylated III Glc ( P ‐III Glc ) has a slightly lower mobility during sodium dodecyl sulphate/polyacrylamide gel electrophoresis than III Glc . In bacterial extracts both phospho enol pyruvate (the physiological phosphoryl donor of the PTS) as well as ATP can phosphorylate III Glc . The ATP‐catalyzed reaction is dependent on phospho enol pyruvate synthase, however, and is due to prior conversion of ATP to phospho enol pyruvate. The phosphoryl group of phosphorylated III Glc is hydrolysed after boiling in sodium dodecyl sulfate but phosphorylated III Glc can be discriminated from III Glc if treated with this detergent at room temperature. We have used the different mobilities of III Glc and P ‐III Glc to estimate the proportion of these two forms in intact cells. Wild‐type cells contain predominantly P ‐III Glc in the absence of PTS sugars. In an S. typhimurium mutant containing a leaky ptsI17 mutation (0.1% enzyme I activity remaining) both forms of III Glc occur in approximately equal amounts. Addition of PTS sugars such as glucose results, both in wild‐type and mutant, in a dephosphorylation of P ‐III Glc . This correlates well with the observed inhibition of non‐PTS uptake systems by PTS sugars via nonphosphorylated III Glc .