Flavoenzyme involved in polyamine back-conversion (Ref.4, PubMed:16331971). Catalyzes the oxidation of the secondary amino group of polyamines, such as spermine, spermidine and their acetyl derivatives (Ref.4, PubMed:16331971). Plays an important role in the regulation of polyamine intracellular concentration (Probable). H2O + O2 + spermidine = 4-aminobutanal + H2O2 + propane-1,3-diamine H2O + N(8)-acetylspermidine + O2 = 4-acetamidobutanal + H2O2 + propane-1,3-diamine H2O + O2 + spermine = H2O2 + N-(3-aminopropyl)-4-aminobutanal + propane-1,3-diamine H2O + N(1)-acetylspermine + O2 = H2O2 + N-(3-acetamidopropyl)-4-aminobutanal + propane-1,3-diamine Binds 1 FAD per subunit. Optimum pH is 6.5. Amine and polyamine degradation; spermine degradation. Monomer. Induced by light (at protein level) (PubMed:12586904). Down-regulated by auxin (at protein level) (PubMed:12586904). Belongs to the flavin monoamine oxidase family.