IUBMB Enzyme Nomenclature


Accepted name: ubiquinol oxidase (electrogenic, proton-motive force generating)

Reaction: 2 ubiquinol + O2[side 2] + 4 H+[side 2] = 2 ubiquinone + 2 H2O[side 2] + 4 H+[side 1] (overall reaction)
(1a) 2 ubiquinol = 2 ubiquinone + 4 H+[side 1] + 4 e-
(1b) O2[side 2] + 4 H+[side 2] + 4 e- = 2 H2O[side 2]

Other name(s): ubiquinol oxidase (electrogenic, non H+-transporting); cytochrome bd-I oxidase; cydA (gene name); cydB (gene name); ubiquinol:O2 oxidoreductase (electrogenic, non H+-transporting)

Systematic name: ubiquinol:oxygen oxidoreductase (electrogenic, non H+-transporting)

Comments: This terminal oxidase enzyme is unable to pump protons but generates a proton motive force by transmembrane charge separation resulting from utilizing protons and electrons originating from opposite sides of the membrane to generate water. The bioenergetic efficiency (the number of charges driven across the membrane per electron used to reduce oxygen to water) is 1. The bd-I oxidase from the bacterium Escherichia coli is the predominant respiratory oxygen reductase that functions under microaerophilic conditions in that organism. cf. EC, ubiquinol oxidase (H+-transporting).

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:


1. Miller, M.J., Hermodson, M. and Gennis, R.B. The active form of the cytochrome d terminal oxidase complex of Escherichia coli is a heterodimer containing one copy of each of the two subunits. J. Biol. Chem. 263 (1988) 5235-5240. [PMID: 3281937]

2. Puustinen, A., Finel, M., Haltia, T., Gennis, R.B. and Wikstrom, M. Properties of the two terminal oxidases of Escherichia coli. Biochemistry 30 (1991) 3936-3942. [PMID: 1850294]

3. Belevich, I., Borisov, V.B., Zhang, J., Yang, K., Konstantinov, A.A., Gennis, R.B. and Verkhovsky, M.I. Time-resolved electrometric and optical studies on cytochrome bd suggest a mechanism of electron-proton coupling in the di-heme active site. Proc. Natl. Acad. Sci. USA 102 (2005) 3657-3662. [PMID: 15728392]

4. Lenn, T., Leake, M.C. and Mullineaux, C.W. Clustering and dynamics of cytochrome bd-I complexes in the Escherichia coli plasma membrane in vivo. Mol. Microbiol. 70 (2008) 1397-1407. [PMID: 19019148]

[EC created 2014 as EC, modified 2017, transferred 2018 to EC]

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