The mechanism of glucose 6-phosphate transport by Escherichia coli.
To evaluate anion exchange as the mechanistic basis of sugar phosphate transport, natural and artificial membranes were used in studies of glucose 6-phosphate (Glc-6-P) and inorganic phosphate (Pi) accumulation by the uhpT-encoded protein (UhpT) of Escherichia coli. Experiments with intact cells demonstrated that UhpT catalyzed the neutral exchange of internal and external Pi, and work with everted as well as right-side-out membrane vesicles showed further that UhpT mediated the heterologous exchange of Pi and Glc-6-P. When loaded with Pi, but not when loaded with morpholinopropanesulfonate (MOPS), everted vesicles took up Glc-6-P to levels 100-fold above medium concentration in a reaction unaffected by the ionophores valinomycin, valinomycin plus nigericin, and carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Similarly, right-side-out vesicles were capable of Glc-6-P transport, but only if a suitable internal countersubstrate was available. Thus, in MOPS-loaded vesicles, oxidative metabolism established a proton-motive force that supported proline or Pi accumulation, but transport of Glc-6-P was found only if vesicles could accumulate Pi during a preincubation. After reconstitution of UhpT into proteoliposomes it was possible to show as well that the level of accumulation of Glc-6-P (17 to 560 nmol/mg of protein) was related directly to the internal concentration of Pi. These results are most easily understood if the transport of glucose 6-phosphate in E. coli occurs by anion exchange rather than by nH+/anion support.
Sonna
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Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Ambudkar
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Maloney
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D001692:Biological Transport / Q000187:drug effects; D002021:Buffers; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D009025:Morpholines; D010710:Phosphates / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D013045:Species Specificity
D002021:Buffers; D005958:Glucosephosphates; D008081:Liposomes; D009025:Morpholines; D010710:Phosphates; D011510:Proteolipids; C020485:proteoliposomes; C008550:morpholinopropane sulfonic acid; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D019298:Glucose-6-Phosphate; D011392:Proline