Group Translocation of Glucose and Other Carbohydrates by the Bacterial Phosphotransferase System

Abstract

Publisher Summary This chapter highlights group translocation of glucose and other carbohydrates by the bacterial phosphotransferase system (PTS). The chapter describes the structure and function of transporters of the bacterial PTS. Group translocation includes the coupling of solute translocation with a chemical modification of the transported solute. Cell-free extracts of Escherichia coli ( E.coli ) catalyzes phosphorylation of glucose with phosphoenolpyruvate rather than ATP as the phosphoryl donor. The fractionation of the extract into membrane and cytoplasmic components revealed that both are necessary for the phosphorylation of glucose. The two complementing activities are designated “enzyme I” and “enzyme II.” In addition, the cytoplasmic extract contains two complementing activities that are designated “enzyme I” and “HPr” (for a heat-stable protein). These two cytoplasmic proteins are phosphoryl carrier proteins that sequentially transfer a phosphoryl group from phosphoenolpyruvate to the membrane-bound, sugar-specific transporters. The PTS comprises over a dozen mutually interacting proteins, the genes of which are spread all over the bacterial chromosome. In E. coli , the genes ptsH and ptsI for HPr and enzyme I, respectively, constitute an operon at 52 min. Immediately downstream of this operon but only partly coregulated with it is crr , which is the gene encoding the cytoplasmic subunit (III Glc ) of the glucose transporter.