IUBMB Enzyme Nomenclature


Accepted name: hydroxylamine oxidase

Reaction: hydroxylamine + 3 ferricytochrome c = nitric oxide + 3 ferrocytochrome c + 3 H+

Other name(s): HOX

Systematic name: hydroxylamine:ferricytochrome-c oxidoreductase (nitric acid-forming)

Comments: The enzyme, characterized from the anaerobic ammonium-oxidizing (anammox) bacterium Kuenenia stuttgartiensis, is very similar to EC, hydroxylamine dehydrogenase. Both enzymes are homotrimeric enzymes in which each subunit contains seven c-type hemes and one specialized P460-type heme that is bound to a tyrosine residue in an adjacent subunit. However, this enzyme catalyses only the 3 electron oxidation of hydroxylamine, forming nitric oxide, and is not capable of performing further oxidation to form nitrite.

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


1. Maalcke, W.J., Dietl, A., Marritt, S.J., Butt, J.N., Jetten, M.S., Keltjens, J.T., Barends, T.R. and Kartal, B. Structural basis of biological NO generation by octaheme oxidoreductases. J. Biol. Chem. 289 (2014) 1228-1242. [PMID: 24302732]

[EC created 2021]

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