an aldehyde + H2O + O2 = a carboxylate + H(+) + H2O2 Binds 2 [2Fe-2S] clusters. Binds 1 Mo-molybdopterin (Mo-MPT) cofactor per subunit. Aldehyde oxidases (AO) are homodimers and heterodimers of AO subunits. Belongs to the xanthine dehydrogenase family.