Catalyzes the oxidative deamination of biogenic and xenobiotic amines and has important functions in the metabolism of neuroactive and vasoactive amines in the central nervous system and peripheral tissues. Oxidizes both 5-hydroxytryptamine (5-HT) and beta-phenylethylamine (PEA). a secondary aliphatic amine + H2O + O2 = a primary amine + an aldehyde + H2O2 Belongs to the flavin monoamine oxidase family. Probable frameshift identified on the basis of homology with other members of this family.