Proton translocation coupled to formate oxidation in anaerobically grown fermenting Escherichia coli Original Research Article

Proton translocation, coupled to formate oxidation and hydrogen evolution, was studied in anaerobically grown fermenting Escherichia coli JW136 carrying hydrogenase 1 (hya) and hydrogenase 2 (hyb) double deletions. Rapid acidification of the medium by EDTA-treated anaerobic suspension of the whole cells or its alkalization by inverted membranes was observed in response to application of formate. The formate-dependent proton translocation and 2H+–K+ exchange coupled to H2 evolution were sensitive to the uncoupler, carbonylcyanide-m-chlorophenylhydrazone, and to copper ions, inhibitors of hydrogenases. No pH changes were observed in a suspension of formate-pulsed aerobically grown (“respiring”) cells. The apparent H+/formate ratio of 1.3 was obtained in cells oxidizing formate. The 2H+–K+ exchange of the ATP synthase inhibitor N,N′-dicyclohexylcarbodiimide-sensitive ion fluxes does take place in JW136 cell suspension.