Biological Nitrogen Removal Database

A manually curated data resource for microbial nitrogen removal

Enzyme Name Gene Culster Enzyme Commission number KEGG Orthology ID
Ammonia monooxygenase (AMO) amoCABD 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 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
Nitrite oxidoreductase nxrABC
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).