Part of the ammonia monooxygenase complex, which catalyzes the oxidation of ammonia to hydroxylamine, the first reaction in the process of ammonia oxidation to nitrite. AH2 + NH4(+) + O2 = A + H(+) + H2O + hydroxylamine Binds 2 copper ions per subunit (PubMed:19453274, PubMed:20204476). The two coppers forms a binuclear cluster (By similarity). In vitro, inhibited by acetylene. kcat is 20 sec(-1) for ammonia as substrate. The soluble ammonia monooxygenase is a nonamer composed of three alpha subunits (AmoA), three beta subunits (AmoB) and three gamma subunits (Cytochrome c1 PetC). Ammonia monooxygenase is active and distributed approximately equally in both subcellular fractions. Cells lacking amoB1 grow more slowly than wild-type cells, while cells lacking amoB2 grow at rates similar to wild-type. The physiological significance of the two gene copies is still unknown.