Could be involved in assimilation and/or detoxification of hydroxylamine, which is a toxic compound that may be formed during nitrate/nitrite assimilation. Catalyzes the reduction of hydroxylamine to form NH(3) and H(2)O. It has a low reductase activity with FAD, FMN, benzyl viologen and bromphenol blue as electrons donors, but it is not able to use NAD or NADP. A + H2O + NH4(+) = AH2 + H(+) + hydroxylamine Binds 1 [4Fe-4S] cluster. Binds 1 hybrid [4Fe-2O-2S] cluster. Inhibited by cyanide and by sulfide and iron reagents such as dithioerythritol, 2,2'-dipyridyl and o-phenanthroline. Optimum pH i 9.3. Optimum temperature is 40 degrees Celsius. Cells lacking this gene are unable to grow with hydroxylamine as the sole nitrogen source. Belongs to the HCP family.