Spermine oxidase is the polyamine oxidase. This enzyme potentially represents a new class of catabolic enzymes in the mammalian polyamine metabolic pathway capable of the efficient oxidation of polyamines. More than five transcript variants encoding four active isoenzymes have been identified for this gene, however, not all variants have been fully described. The characterized isoenzymes have distinctive biochemical characteristics and substrate specificities, suggesting the existence of additional levels of complexity in polyamine catabolism.Plays an important role in the regulation of polyamine intracellular concentration and has the potential to act as a determinant of cellular sensitivity to the antitumor polyamine analogs. May contribute to beta-alanine production via aldehyde dehydrogenase conversion of 3-amino-propanal.