EC - Ubiquinol oxidase (non-electrogenic)

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IntEnz Enzyme Nomenclature


Accepted name:
ubiquinol oxidase (non-electrogenic)
Other names:
plant alternative oxidase
cyanide-insensitive oxidase
AOX (gene name)
ubiquinol oxidase
Systematic name:
ubiquinol:O2 oxidoreductase (non-electrogenic)




The enzyme, described from the mitochondria of plants and some fungi and protists, is an alternative terminal oxidase that is not sensitive to cyanide inhibition and does not generate a proton motive force. Unlike the electrogenic terminal oxidases that contain hemes (cf. EC and EC, this enzyme contains a dinuclear non-heme iron complex. The function of this oxidase is believed to be dissipating excess reducing power, minimizing oxidative stress, and optimizing photosynthesis in response to changing conditions.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0102721
UniProtKB/Swiss-Prot: (18) [show] [UniProt]


  1. Bendall, D. S., Bonner, W. D.
    Cyanide-insensitive respiration in plant mitochondria.
    Plant Physiol. 47: 236-245 (1971). [PMID: 16657603]
  2. Siedow, J. N., Umbach, A. L., Moore, A. L.
    The active site of the cyanide-resistant oxidase from plant mitochondria contains a binuclear iron center.
    FEBS Lett. 362: 10-14 (1995). [PMID: 7698344]
  3. Berthold, D. A., Andersson, M. E., Nordlund, P.
    New insight into the structure and function of the alternative oxidase.
    Biochim. Biophys. Acta 1460: 241-254 (2000). [PMID: 11106766]
  4. Williams, B. A., Elliot, C., Burri, L., Kido, Y., Kita, K., Moore, A. L., Keeling, P. J.
    A broad distribution of the alternative oxidase in microsporidian parasites.
    PLoS Pathog. 6: e1000761 (2010). [PMID: 20169184]
  5. Gandin, A., Duffes, C., Day, D. A., Cousins, A. B.
    The absence of alternative oxidase AOX1A results in altered response of photosynthetic carbon assimilation to increasing CO(2) in Arabidopsis thaliana.
    Plant Cell Physiol. 53: 1627-1637 (2012). [PMID: 22848123]

[EC created 2011, modified 2014]