Studies on the Uptake of Hexose Phosphates

A wild strain of Escherichia coli utilizes glucose 1-phosphate by hydrolysis of the ester at the cell surface, after which the glucose moiety but not the phosphate group enters the cell. However, when these cells are induced by treatment with glucose 6-phosphate, they are able to take up both glucose 6-phosphate and glucose 1-phosphate without preliminary hydrolysis. Mutant strains of E. coli that lack Enzyme I of the phosphotransferase system are unable to grow in the presence of glucose or glucose 1-phosphate as a carbon source. These strains show uptake of 14C-glucose 1-phosphate after being induced with glucose 6-phosphate. Mutant strains have been isolated that lack Enzyme I and are constitutive for the hexose phosphate transport system. They can grow on glucose 6-phosphate or glucose 1-phosphate, but not on glucose as carbon source. In these strains the uptake of 14C-glucose 1-phosphate involves entry of the entire molecule, and uptake is inhibited by glucose 6-phosphate. It is concluded that glucose 1-phosphate may be used by E. coli after preliminary hydrolysis by a surface phosphatase which is effective at neutral pH. In addition, glucose 1-phosphate is a substrate, but not an inducer, for the hexose phosphate transport system that is active with glucose 6-phosphate and related compounds.