The enzymes from the nitrifying bacterium Nitrosomonas europaea [1,4] and the methylotrophic bacterium Methylococcus capsulatus  are hemoproteins with seven c-type hemes and one specialized P-460-type heme per subunit. The enzyme converts hydroxylamine to nitrite via an enzyme-bound nitroxyl intermediate . While nitrite is the main product, the enzyme from Nitrosomonas europaea can produce nitric oxide as well .
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[EC 126.96.36.199 created 1972 as EC 188.8.131.52, part transferred 2012 to EC 184.108.40.206]