The symbiotically essentialcbb3‐type oxidase ofBradyrhizobium japonicumis a proton pump

Abstract

Purifiedcbb3‐type oxidase ofBradyrhizobium japonicumwas reconstituted into phospholipid vesicles. Tight vesicles were obtained as shown by the disturbance of ΔpH with CCCP and the membrane potential with valinomycin, which led to a six‐fold increase in cytochromecoxidase activity. The vesicles were thus suitable for proton translocation experiments. In the presence of valinomycin, a pulse with reduced cytochromeccaused an acidification with a subsequent alkalinization, whereas the same pulse caused only an alkalinization in the presence of valinomycin plus CCCP. We conclude that thecbb3‐type oxidase ofB. japonicumis a proton pump.