Ubiquinol oxidase (H<sup>+</sup>-transporting) (, cytochrome bb3 oxidase, cytochrome bo oxidase, cytochrome bd-I oxidase) is an enzyme with systematic name ubiquinol:O<sub>2</sub> oxidoreductase (H<sup>+</sup>-transporting). This enzyme catalyses the following chemical reaction
Ubiquinol oxidase contains a dinuclear centre comprising two hemes, or heme and copper.