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 (P(i)) 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 P(i), and work with everted as well as right-side-out membrane vesicles showed further that UhpT mediated the heterologous exchange of P(i) and Glc-6-P. When loaded with P(i), 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 P(i) accumulation, but transport of Glc-6-P was found only if vesicles could accumulate P(i) 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 P(i). 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 symport.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - 1988|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology