Evidence for an electrogenic 3-deoxy-2-oxo-d-gluconate–proton co-transport driven by the protonmotive force in Escherichia coli K12

Abstract

Evidence is presented indicating that the carrier-mediated uptake of 3-deoxy-2-oxo-D-gluconate and D-glucuronate in E. coli K12 is driven by the .DELTA.pH [pH gradient] and .DELTA..psi. [membrane potential] components of the protonmotive force. Approximately 2 protons enter the cells with each sugar molecule, independent of the sugar and the strain used. In respiring cells, the magnitude of the .DELTA.pH alone, as measured by distribution of [3H]acetate, appears to be insufficient to account for the chemical gradient of 3-deoxy-2-oxo-D-gluconate that is developed between pH 6.0-8.0. If the external pH is varied between 5.5-8.0, 3-deoxy-2-oxo-D-gluconate uptake is gradually inhibited by valinomycin plus K+ ions, but the inhibition caused by nigericin is concomitantly relieved, thus reflecting the relative contribution of .DELTA.pH and .DELTA..psi. to the total protonmotive force at each external pH. 3-Deoxy-2-oxo-D-gluconate can be transiently accumulated into isolated membrane vesicles in response to an artificially induced pH gradient. The process is stimulated when the membrane potential is collapsed by valinomycin in the presence of K+ ions.