EC - Hydroxylamine oxidase (cytochrome)

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IntEnz Enzyme Nomenclature


Accepted name:
hydroxylamine oxidase (cytochrome)
Other names:
HAO [ambiguous]
hydroxylamine oxidoreductase [ambiguous]
hydroxylamine oxidase [misleading]
Systematic name:
hydroxylamine:oxygen oxidoreductase




The enzyme from the heterotrophic nitrifying bacterium Paracoccus denitrificans contains three to five non-heme, non-iron-sulfur iron atoms and interacts with cytochrome c556 and pseudoazurin [2,3]. Under anaerobic conditions in vitro only nitrous oxide is formed [3]. Presumably nitroxyl is released and combines with a second nitroxyl to give nitrous oxide and water. When oxygen is present, nitrite is formed.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB


  1. Kurokawa, M, Fukumori, Y and Yamanaka, T
    A hydroxylamine - cytochrome C reductase occurs in the heterotrophic nitrifier Arthrobacter globiformis.
    Plant Cell Physiol. 26: 1439-1442 (1985).
  2. Wehrfritz, J. M., Reilly, A., Spiro, S., Richardson, D. J.
    Purification of hydroxylamine oxidase from Thiosphaera pantotropha. Identification of electron acceptors that couple heterotrophic nitrification to aerobic denitrification.
    FEBS Lett. 335: 246-250 (1993). [PMID: 8253206]
  3. Moir, J. W., Wehrfritz, J. M., Spiro, S., Richardson, D. J.
    The biochemical characterization of a novel non-haem-iron hydroxylamine oxidase from Paracoccus denitrificans GB17.
    Biochem. J. 319: 823-827 (1996). [PMID: 8920986]
  4. Wehrfritz, J., Carter, J. P., Spiro, S., Richardson, D. J.
    Hydroxylamine oxidation in heterotrophic nitrate-reducing soil bacteria and purification of a hydroxylamine-cytochrome c oxidoreductase from a Pseudomonas species.
    Arch. Microbiol. 166: 421-424 (1996). [PMID: 9082922]

[EC created 1972 as EC, part transferred 2013 to EC, modified 2015]