The electrochemical proton gradient generated by the fumarate-reductase system in Escherichia coli and its bioenergetic implications.

Proton translocation, coupled to electron transfer in the fumarate reductase system, generates and electrochemical potential gradient for protons (delta approximately mu H+). The magnitude of this free energy gradient has been determined in the Escherichia coli strains ML 208-225 and AN 283. The measurements were performed in (inverted) membrane particles, right-side out membrane vesicles and EDTA-treated intact cells in external media of various ionic compositions and pH. The maximal values of delta approximately mu H+ in these three systems were +103, -101 and -105 mV, respectively. This implicates that in E. coli, upon transition from oxygen to fumarate as electron acceptor, the magnitude of the delta approximately mu H+ decreases considerably. This change of delta approximately mu H+ has substantial consequences for the cellular metabolism.