Abstract
Abstract Membranes prepared from Escherichia coli induced or constitutive for glucose 6-phosphate transport accumulate this compound from the medium. The transport is independent of the phosphotransferase system, insofar as a mutant deficient in Enzyme I of this system yields membranes fully active in glucose 6-phosphate uptake; and the addition of phosphoenolpyruvate to induced wild type membranes did not stimulate glucose 6-phosphate uptake. Both the rate and extent of uptake are, however, stimulated several-fold in the presence of either d(-)-lactate or succinate. In the case of the d(-)-lactic dehydrogenase activity there is far more pyruvate produced than glucose 6-phosphate transported. Evidence presented indicates that it is the free glucose 6-phosphate which is accumulated, and that this material is freely exchangeable with external compound.
Highlights
E’scherichia coli is capable of growth on glucose-6-P (l), because it possesses an inducible active transport system for this compound [2, 3]. This system is independent of glucose transport, since glucose-negative cells grow on glucose-6-P
A specific genetic locus for glucose-6-P transport has been mapped, and it is distinct from those known loci for glucose uptake [4]
We have recently shown that glucose-6-P transport in E. coli may be induced, and is fully active, in a mutant deficient in Enzyme I of the phosphotransferase system, suggesting that this system is not involved in glucose-6-P uptake [10]
Summary
Membranes prepared from Escherichia coli induced or constitutive for glucose 6-phosphate transport accumulate this compound from the medium. The transport is independent of the phosphotransferase system, insofar as a mutant deficient in Enzyme I of this system yields membranes fully active in glucose 6-phosphate uptake; and the addition of phosphoenolpyruvate to induced wild type membranes did not stimulate glucose 6-phosphate uptake. Both the rate and extent of uptake are, stimulated several-fold in the presence of either D( -)-lactate or succinate. We have recently shown that glucose-6-P transport in E. coli may be induced, and is fully active, in a mutant deficient in Enzyme I of the phosphotransferase system, suggesting that this system is not involved in glucose-6-P uptake [10]. In order to further characterize the glucose-6-P uptake mechanism in E. coli, we have prepared a membrane fraction from glucose-6-P-induced cells, and studied the effects of various compounds on its transport
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