IUBMB Enzyme Nomenclature


Accepted name: ubiquinol oxidase (H+-transporting)

Reaction: 2 ubiquinol + O2 + n H+[side 1] = 2 ubiquinone + 2 H2O + n H+[side 2]

Other name(s): cytochrome bb3 oxidase; cytochrome bo-oxidase; cytochrome bd-II oxidase; ubiquinol:O2 oxidoreductase (H+-transporting)

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

Comments: Contains a dinuclear centre comprising two hemes, or heme and copper. This terminal oxidase enzyme generates proton motive force by two mechanisms: (1) transmembrane charge separation resulting from utilizing protons and electrons originating from opposite sides of the membrane to generate water, and (2) active pumping of protons across the membrane. The bioenergetic efficiency (the number of charges driven across the membrane per electron used to reduce oxygen to water) depends on the enzyme; for example, for the bo3 oxidase it is 2, while for the bd-II oxidase it is 1. cf. EC, ubiquinol oxidase (electrogenic, non H+-transporting).

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


1. Abramson, J., Riistama, S., Larsson, G., Jasaitis, A., Svensson-Ek, M., Laakkonen, L., Puustinen, A., Iwata, S. and Wikstrom, M. The structure of the ubiquinol oxidase from Escherichia coli and its ubiquinone binding site. Nat. Struct. Biol. 7 (2000) 910-917. [PMID: 11017202]

2. Yap, L.L., Lin, M.T., Ouyang, H., Samoilova, R.I., Dikanov, S.A. and Gennis, R.B. The quinone-binding sites of the cytochrome bo3 ubiquinol oxidase from Escherichia coli. Biochim. Biophys. Acta 1797 (2010) 1924-1932. [PMID: 20416270]

3. Shepherd, M., Sanguinetti, G., Cook, G.M. and Poole, R.K. Compensations for diminished terminal oxidase activity in Escherichia coli: cytochrome bd-II-mediated respiration and glutamate metabolism. J. Biol. Chem. 285 (2010) 18464-18472. [PMID: 20392690]

4. Borisov, V.B., Murali, R., Verkhovskaya, M.L., Bloch, D.A., Han, H., Gennis, R.B. and Verkhovsky, M.I. Aerobic respiratory chain of Escherichia coli is not allowed to work in fully uncoupled mode. Proc. Natl. Acad. Sci. USA 108 (2011) 17320-17324. [PMID: 21987791]

[EC created 2011, modified 2014]

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