Flavoenzyme involved in polyamine back-conversion (PubMed:21796433). Catalyzes the oxidation of the secondary amino group of polyamines, such as spermine, spermidine and their acetyl derivatives (PubMed:21796433). Substrate preference is spermidine > norspermine > thermospermine > N(1)-acetylspermine > spermine (PubMed:21796433). No activity detected when putrescine is used as substrate (PubMed:21796433). Plays an important role in the regulation of polyamine intracellular concentration (Probable). H2O + O2 + spermine = 3-aminopropanal + H2O2 + spermidine H2O + N(1)-acetylspermine + O2 = 3-acetamidopropanal + H2O2 + spermidine H2O + norspermine + O2 = 3-aminopropanal + H2O2 + norspermidine H2O + O2 + spermidine = 3-aminopropanal + H2O2 + putrescine H2O + O2 + thermospermine = 3-aminopropanal + H2O2 + spermidine Binds 1 FAD per subunit. Amine and polyamine degradation; spermine degradation. Amine and polyamine degradation; spermidine degradation. Widely expressed. Belongs to the flavin monoamine oxidase family.