Respiration-linked proton flux in Wolinella succinogenes during reduction of N-oxides

Abstract

Formate uncoupled proton translocation in formate-grown Wolinella succinogenes cells supplied with N-oxides as terminal electron acceptors. In suspensions containing KSCN (but not valinomycin), H 2 supported proton translocation when NO 3 −, NO 2 −, and NO were provided as oxidants. H +/ N-oxide ratios were 4.77 for NO 3 −, 2.49 for NO 2 −, and 1.75 for NO. KSCN inhibits N 2O reduction thus precluding use of N 2O as oxidant. Repeated exposure of cells to NO inhibited their ability to translocate protons with NO as oxidant but only slightly diminished and did not eliminate their capacity for NO 3 −- or NO 2 −-dependent proton flux. Substituting reduced benzyl viologen for H 2 and measuring proton uptake provided results consistent with an extramembranal location for the N-oxide reductases. The uncoupler, carbonyl cyanide m-chlorophenylhydrazone, collapsed proton gradients, permitted uptake of 2 mol H +/mol NO 3 − or NO 2 −, but unaccountably inhibited NO 3 − reduction by 50% while leaving H + uptake stoichiometry of the cells unaffected.