Description:
<jats:p>Purified<jats:italic>cbb</jats:italic><jats:sub>3</jats:sub>‐type oxidase of<jats:italic>Bradyrhizobium japonicum</jats:italic>was 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 cytochrome<jats:italic>c</jats:italic>oxidase activity. The vesicles were thus suitable for proton translocation experiments. In the presence of valinomycin, a pulse with reduced cytochrome<jats:italic>c</jats:italic>caused an acidification with a subsequent alkalinization, whereas the same pulse caused only an alkalinization in the presence of valinomycin plus CCCP. We conclude that the<jats:italic>cbb</jats:italic><jats:sub>3</jats:sub>‐type oxidase of<jats:italic>B. japonicum</jats:italic>is a proton pump.</jats:p>