Flavoenzyme involved in polyamine back-conversion (PubMed:18583528, PubMed:20532512, PubMed:21081665). Catalyzes the oxidation of the secondary amino group of polyamines, such as spermine, spermidine and their acetyl derivatives (PubMed:18583528, PubMed:20532512, PubMed:21081665). Substrate preference is spermidine > spermine > N(1)-acetylspermidine > N(1)-acetylspermine (PubMed:18583528). Plays an important role in the regulation of polyamine intracellular concentration (Probable). Involved in the production of hydrogen peroxide during pollen tube growth (PubMed:20626657). Hydrogen peroxide triggers the opening of the hyperpolarization-activated calcium permeable channels in pollen, and thus regulates pollen tube growth (PubMed:20626657). H2O + O2 + spermine = 3-aminopropanal + H2O2 + spermidine H2O + O2 + spermidine = 3-aminopropanal + H2O2 + putrescine H2O + N(1)-acetylspermine + O2 = 3-acetamidopropanal + H2O2 + spermidine H2O + N(1)-acetylspermidine + O2 = 3-acetamidopropanal + H2O2 + putrescine H2O + O2 + thermospermine = 3-aminopropanal + H2O2 + spermidine Binds 1 FAD per subunit. Inhibited by guazatine, aminoguanidine and putrescine. Optimum pH is 7.5. No activity at pH above 9.5 or below 6.5. Optimum temperature is 37 degrees Celsius. Amine and polyamine degradation; spermine degradation. Amine and polyamine degradation; spermidine degradation. Expressed at similar levels in all tissues tested. Highest expression is seen in siliques. By abscisic acid, jasmonate, salicylic acid, wounding and flagellin 22, a pathogen elicitor. Belongs to the flavin monoamine oxidase family.