Catalyzes the degradation of compounds such as putrescine, histamine, spermine, and spermidine, substances involved in allergic and immune responses, cell proliferation, tissue differentiation, tumor formation, and possibly apoptosis. Placental DAO is thought to play a role in the regulation of the female reproductive function. H2O + histamine + O2 = H2O2 + imidazole-4-acetaldehyde + NH4(+) Binds 1 copper ion per subunit. Binds 2 calcium ions per subunit. Contains 1 topaquinone per subunit. Inhibited by isoniazid, cimetidine, clonidine, pentamidine, berenil and pentamidine. Homodimer; disulfide-linked. Placenta and kidney. Topaquinone (TPQ) is generated by copper-dependent autoxidation of a specific tyrosyl residue. Inhibited by amiloride in a competitive manner. Belongs to the copper/topaquinone oxidase family.