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

Hydrogen formation from formate by cell suspensions of E. coli JW136 resulted in the formation of a membrane potential (Δψ) across the cytoplasmic membrane of −130 mV (inside negative). This was abolished in the presence of copper ions, although they had little effect on the value of Δψ generated by E. coli under respiration. We conclude that the hydrogen production by hydrogenase 3 is coupled to formate-dependent proton pumping that regulates 2H+-K+ exchange in fermenting bacteria.