Hydroxylamine Oxidoreductase

Hydroxylamine oxidoreductase (HAO) is an enzyme found in the prokaryote Nitrosomonas europaea. It plays a critically important role in the biogeochemical nitrogen cycle as part of the metabolism of ammonia-oxidizing bacteria. Hydroxylamine oxidoreductase (HAO) is an enzyme found in the prokaryote Nitrosomonas europaea. It plays a critically important role in the biogeochemical nitrogen cycle as part of the metabolism of ammonia-oxidizing bacteria. The substrate is hydroxylamine ( NH 2 OH {displaystyle {{ce {NH2OH}}}} ), a chemical produced biologically by the enzyme Ammonia monooxygenase. The products of the catalyzed reaction are debated, but recent work shows compelling evidence for the production of nitric oxide. Crystallographic methods show that HAO (PDB code: 1FGJ) is a cross-linked trimer of polypeptides containing 24 heme cofactors. For many decades the enzyme was thought to catalyze the following reaction: Recent work in the field, however, reveals that this enzyme catalyzes an entirely different reaction: