Monoamine oxidases (MAOs) are a family of enzymes that oxidize a number of biogenic amines through the production of hydrogen peroxide (H2O2). Two members of the MAO family have been identified and designated, MAO A and MAO B, which are encoded by two homologous genes comprising 15 exons with identical intro-exon organization and exhibit substrate-specificity. MAO A displays higher affinity towards serotonin, norepinephrine and dopamine; while MAO B displays higher affinity towards phenylethylamine and benzylamine.  Four highly conserved regions associated with the catalytic activity of mammalian MAO enzymes have been identified, including an ADP binding β-α-β unit, a putative substrate-binding domain, a FAD covalent attachment site, and a C terminus region predicted to form a transmembrane-associated α-helix.