Studies on the uptake of hexose phosphates. II. The induction of the glucose 6-phosphate transport system by exogenous but not by endogenously formed glucose 6-phosphate.

An Escherichia coli mutant, DF2000, accumulates up to 0.06 M glucose 6-phosphate when supplied glucose. This extremely large concentration of intracellular glucose 6-phosphate does not serve to induce the active transport of this ester. However, if the medium is then supplemented with only 5 X 1O-4 M glucose 6-phosphate the transport system is induced. Thus, it appears that exogenous glucose 6-phosphate acts as an inducer but the endogenously formed ester is unable to do so. The ester accumulated by glucosetreated cells was isolated and purified. It proved to be an effective inducer of glucose 6-phosphate transport. The transport system for glucose 6-phosphate allows this ester to accumulate until the intracellular concentration is 20-fold greater than the concentration in the medium. When glucose-treated cells containing 0.06 M glucose 6-phosphate are induced for transport with 5 X 1O-4 M ester the initial concentration ratio is 120: 1. Consequently, glucose B-phosphate exits from the newly induced cells until a concentration ratio of 20: 1 is established. Accumulation of glucose 6-phosphate by cells of the mutant given glucose results in growth stasis. This toxic effect is reduced or prevented by inducing levels of glucose 6-phosphate in the medium.