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 1 copper ion per subunit. In vitro, inhibited by acetylene (PubMed:19453274). In fact, acetylene is oxidized to ketene which binds irreversibly to His-191 of ammonia monooxygenase alpha subunit (AmoA) (PubMed:19118368). kcat is 20 sec(-1) for ammonia. 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 amoA1 grow more slowly than wild-type cells, while cells lacking amoA2 grow at rates similar to wild-type. The physiological significance of the two gene copies is still unknown.