External succinate and potassium ions influence Dcu dependent F_OF₁-ATPase activity and H⁺ flux of Escherichia coli at different pHs

During fermentation Escherichia coli transport succinate mainly via Dcu family carriers. Current paper describes the role of externally added succinate on N'N'-dicyclohexylcarbodiimide (DCCD) sensitive ATPase activity and H⁺ flux depending on potassium ions. At pH 7.5 in wild type membrane vesicles DCCD-sensitive ATPase activity was the same as in dcuACBD quadruple mutant. In dcuACB it was increased ~ 3.3 fold while in dcuD DCCD-sensitive ATPase activity was absent. The DCCD-sensitive H⁺ efflux was fully dependent on F_OF₁ only in dcuACB mutant. This activity depended on potassium ions and only in dcuACBD mutant DCCD-sensitive ATPase activity was stimulated ~ 3 fold. At pH 5.5 DCCD-sensitive ATPase activities were determined in dcuACB or dcuD mutants but not in wild type. Interestingly, addition of potassium ions enhanced DCCD-sensitive ATPase activity in dcuD mutant ~ 3-fold compared to wild type. In dcuD mutant ~ 3-fold higher H⁺ uptake was registered, compared to wild type. Taken together it can be concluded that at pH 7.5 the F_OF₁-activity depends on DcuACB. Moreover, DcuACB but not DcuD are working towards H⁺ uptake direction. DcuD contributes to H⁺ efflux at pH 7.5 while at pH 5.5 it affects H⁺ influx when external succinate is present.