|Enzyme Name||Gene Culster||Enzyme Commission number||KEGG Orthology ID||
|Ammonia monooxygenase (AMO)||amoCABD||184.108.40.206||K10944
|Ammonia monooxygenase (AMO) catalyzes the oxidation of ammonia to hydroxylamine, the first reaction in the process of ammonia oxidation to nitrite.||Link|
|Hydroxylamine oxidoreductase||haoAB||220.127.116.11||K10535||The enzyme catalyzes the oxidation of hydroxylamine to nitrite via an enzyme-bound nitroxyl intermediate. The main product is nitrite, in some cases nitric oxide is produced as well.||Link|
|The enzyme catalyzes the oxidation of nitrite to nitrate via an enzyme-bound nitroxyl intermediate. Under unaerobic conditions the enzyme is a nitrate reductase, catalyzing the reverse reaction.
All known NOB oxidize nitrite by the enzyme NXR, which belongs to the type II group in the dimethyl sulfoxide reductase family of molybdopterin-cofactor-binding enzymes (Meincke et al., 1992; Lücker et al., 2010). NXR is membrane associated and contains an α subunit (NxrA) with the catalytic site and a β subunit (NxrB) that channels electrons derived from nitrite to downstream components of the respiratory chain (Kirstein and Bock, 1993). Most likely, a γ subunit (NxrC) functions as a membrane anchor that may be involved in electron transport (Lücker et al., 2010).