Oxidative phosphorylation in Escherichia coli

Abstract

A particulate fraction obtained from sonic extracts of Escherichia coli was able to carry out oxidative phosphorylation with NADH2 as substrate and to perform the energy-dependent transhydrogenase reaction. The latter activity was more stable, suggesting that different coupling factors were involved in both systems. A coupling-factor preparation stimulated both reactions but to differing degrees. Oxidative phosphorylation was more sensitive than the transhydrogenase to irradiation with ultraviolet light, which destroyed a site located between flavin and cytochrome b1 in the respiratory chain. Experiments with dicumarol and pentachlorophenol suggested that these inhibitors and the coupling-factor preparation also interacted with the electron-transport chain at this site. Further evidence for the existence of two sites of energy coupling was obtained by the selective inhibition of the transhydrogenase by carbonyl cyanide m-chlorophenylhydrazone, EDTA, triiodothyronine, 2,4-dinitrophenol, and hydroxylamine. The effects of calcium and of phosphate ions were consistent with the involvement of non-phosphorylated high-energy intermediates in oxidative phosphorylation and the energy-dependent transhydrogenase.