Carbohydrate uptake by Escherichia coli.

In contrast to active transport, the uptake of carbohydrates via the phosphoenolpyruvate-dependent phosphotransferase system (PTS) leads to the appearance in the cell of the sugar initially as a 1- or 6-phosphate ester. The components of the PTS that transfer phosphate to the sugar are not absolutely specific for any one sugar. Both their synthesis and their activity are controlled; in the latter, "fine" control, glucose-6-phosphate appears to play an important role. Studies of growth on, and uptake of, galactose by E.coli mutants devoid of components of the PTS and also devoid of active transport systems for galactose, suggest that proteins effecting facilitated diffusion of hexoses may be part of, or be closely associated with, the sugar-specific components of the PTS.