Transport of lactate and succinate by membrane vesicles of Escherichia coli, Bacillus subtilis and a pseudomonas species.

Abstract

Transport of d‐lactate, l‐lactate and succinate in isolated membrane vesicles of Escherichia coli, Bacillus subtilis and a fresh‐water Pseudomonas species occurs actively by specific transport systems which are linked to the electron transport chain. These substrates are not transported by the membrane vesicles unless an electron donor (reduced phenazine methosulfate, NADH, d‐lactate, l‐lactate, or succinate) is present in the reaction mixture; in the presence of an electron donor, the substrates or their oxidized forms are concentrated several‐fold inside the membrane vesicles; and inhibitors of the electron transport chain markedly inhibit this electron‐donor mediated transport. In addition, transport of pyruvate in membrane vesicles of E. coli, but not in those of B. subtilis and the Pseudomonas sp. is stimulated by reduced phenazine methosulfate. Activity of the membrane‐bound lactate and succinate dehydrogenases is not essential for the transport of lactate and succinate, since inhibitors of these activities have little effect on reduced phenazine methosulfate‐ or NADH‐energized transport of these substrates; and the Km values for oxidation of these substrates by the membrane vesicles are 30‐ to 80‐fold higher than the Km values for their transport. d‐Lactate and l‐lactate cause strong inhibition of the transport of each other in the three organisms, suggesting that the two substrates share a common transport system. In general, transport of these substrates is not inhibited by dicarboxylic acids. In contrast, transport of succinate is strongly inhibited by other dicarboxylic acids in the three organisms, suggesting that these substrates may share a common transport system. The transport systems for lactate and succinate are repressed by glucose.