Spheroplasts from aerobically grown wild‐type Paracoccus denitrificans cells respire with succinate despite specific inhibition of the cytochrome bc 1 complex by myxothiazol. Coupled to this activity, which involves only b‐type cytochromes, there is translocation of 1.5–1.9 H+/e− across the cytoplasmic membrane. Similar H+ translocation ratios are observed during oxidation of ubiquinol in spheroplasts from aerobically grown mutants of Paracoccus lacking cytochrome c oxidase, or deficient in cytochrome c, as well as in a strain of E. coli from which cytochrome d was deleted. These observations show that the cytochrome o complex is a proton pump much like cytochrome aa 3 to which it is structurally related.

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