Bacterial phosphoenolpyruvate-dependent phosphotransferase system. Mechanism of the transmembrane sugar translocation and phosphorylation

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Abstract
The phosphoryl-group transfer from PHPr to glucose or .alpha.-methylglucose and from glucose 6-phosphate to these same sugars catalyzed by membrane-bound EIIBGlc of the bacterial phosphoenolpyruvate-dependent phosphotransferase system was studied in vitro. Kinetic measurements revealed that the phosphorylation reaction and the exchange reaction proceed according to a ping-pong mechanism in which a phosphorylated membrane-bound enzyme II acts as an obligatory intermediate. The occurrence of a phospho-IIBGlc/IIIGlc was physically demonstrated by the production of a glucose 6-phosphate burst from membranes phosphorylated by phosphoenolpyruvate, HPr, and EI. The observation of similar second-order rate constants for the production of sugar phosphate starting with different phosphoryl-group donors confirms the catalytic relevance of the phosphoenzyme IIBGlc intermediate. The in vitro results, together with data published by other investigators, led to a model describing sugar phosphorylation and transport in vivo.

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