Sugar Transport

A phosphotransferase system was isolated from Escherichia coli and was detected in other gram-negative organisms. The system catalyzed the transfer of phosphate from phosphoenolpyruvate to sugars of the d-gluco and d-manno configurations, yielding pyruvate and the corresponding sugar 6-phosphate esters. Fractionation of the enzyme system yielded three protein components, Enzymes I and II, and a histidine-containing protein, designated HPr. Enzyme I catalyzed the transfer of phosphate from phosphoenolpyruvate to HPr. The phosphoryl moiety in phospho-HPr was linked to the protein via an imidazole nitrogen atom of a histidine residue. Enzyme II catalyzed the transfer of phosphate from phospho-HPr to the sugars. Enzyme I and HPr were soluble constituents of the cell, while Enzyme II (or Fraction II) was located in the membrane fraction.