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. 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. Homodimer; disulfide-linked. 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. Truncated N-terminus.