Proton translocation in cytochrome-deficient mutants of Escherichia coli

Abstract

Cytochrome-deficient cells of a strain of Escherichia coli lacking 5-amino-levulinate synthetase have been used to study proton translocation associated with the reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase region of the electron transport chain. Menadione was used as electron acceptor, and mannitol was used as the substrate for the generation of intracellular NADH. The effects of iron deficiency on NADH- and D-lactate-menadione reductase activities were studied in iron-deficient cells of a mutant strain unable to synthesize the iron chelator enterochelin; both activities were reduced. The NADH- menadione reductase activity in cytochrome-deficient cells was associated with proton translocation and could be coupled to the uptake of proline. However proton translocation associated with the NADH-menadione reductase activity was prevented by a mutation in an unc gene. It was concluded that there is no proton translocation associated with the NADH-dehydrogenase region of the electron transport chain in E. coli and that the proton translocation obtained with mannitol as substrate is due to the activity of membrane-bound adenosine triphosphatase.