Evidence for Escherichia coli DcuD carrier dependent F_OF₁-ATPase activity during fermentation of glycerol

During fermentation Escherichia coli excrete succinate mainly via Dcu family carriers. Current work reveals the total and N,N'-dicyclohexylcarbodiimide (DCCD) inhibited ATPase activity at pH 7.5 and 5.5 in E. coli wild type and dcu mutants upon glycerol fermentation. The overall ATPase activity was highest at pH 7.5 in dcuABCD mutant. In wild type cells 50% of the activity came from the F_OF₁-ATPase but in dcuD mutant it reached ~80%. K⁺ (100 mM) stimulate total but not DCCD inhibited ATPase activity 40% and 20% in wild type and dcuD mutant, respectively. 90% of overall ATPase activity was inhibited by DCCD at pH 5.5 only in dcuABC mutant. At pH 7.5 the H⁺ fluxes in E. coli wild type, dcuD and dcuABCD mutants was similar but in dcuABC triple mutant the H⁺ flux decreased 1.4 fold reaching 1.15 mM/min when glycerol was supplemented. In succinate assays the H⁺ flux was higher in the strains where DcuD is absent. No significant differences were determined in wild type and mutants specific growth rate except dcuD strain. Taken together it is suggested that during glycerol fermentation DcuD has impact on H⁺ fluxes, F_OF₁-ATPase activity and depends on potassium ions.