Thermochemical studies of energetics in active transport across Escherichia coli membranes

Abstract

A thermochemical method was shown to be useful in the membrane active transport research. By employing microcalorimetry in conjunction with the reported transport data, the formation of a proton electrochemical potential (Δμ H+) across the membranes was confirmed from the thermochemical point of view. These membranes include proteoliposomes reconstituted from cytochrome o oxidase and membrane lipids as well as membrane vesicles prepared from Escherichia coli. Different electron-donor systems including dithiothreitol-ubiquinone, D-lactate-lactate dehydrogenase and ascorbate-phenazine methosulfate were used to provide the energy source for the active transport. Energetics information including the energy source, the proton electrochemical potential, the energy utilization and the coupling reactions were obtained. The energy transfers in the coupling reactions involving the oxidation of an electron donor and the formation of Δμ H+ were estimated. Comparative results were found in both membrane systems. The characteristic of the created Δμ H+ was independent of the energy source imposed on the membranes.