Bacterial Phosphoenolpyruvate-dependent Phosphotransferase System. Mechanism of the Transmembrane Sugar Translocation and Phosphorylation

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 has been studied in vitro. Kinetic measurements revealed that both 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 has been 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, have led to a model describing sugar phosphorylation and transport in vivo.