A polyamine oxidase (PAO) is an enzymatic flavoprotein that oxidizes a carbon-nitrogen bond in a secondary amino group of a polyamine donor, using molecular oxygen as an acceptor. The generalized PAO reaction converts three substrates (water, oxygen, and a polyamine with both primary and secondary amino groups) into three products (hydrogen peroxide, an amino-aldehyde, and a primary amine). Different PAOs with varying substrate specificities exist in different organisms. Phylogenetic analyses suggest that PAOs likely evolved once in eukaryotes and diversified by divergent evolution and gene duplication events, though some prokaryotes have acquired PAOs through horizontal gene transfer.[1]
| Substrate | Amino-aldehyde Product | Primary Amine Product | EC Identifier | KEGG Reaction |
| Spermine | 3-aminopropanal | Spermidine | EC 1.5.3.16, EC 1.5.3.17 | R09076 |
| Spermidine | 3-aminopropanal | Putrescine | EC 1.5.3.17 | R09077 |
| 4-aminobutanal | 1,3-diaminopropane | EC 1.5.3.14 | R01914 | |
| N1-acetylspermine | N-(3-acetamidopropyl)-4-aminobutanal | 1,3-diaminopropane | EC 1.5.3.15 | NA |
| 3-acetamidopropanal | Spermidine | EC 1.5.3.13, EC 1.5.3.17 | R03899 | |
| N1,N12-diacetylspermine | 3-acetamidopropanal | N1-acetylspermidine | EC 1.5.3.13 | NA |
| N1-acetylspermidine | 3-acetamidopropanal | Putrescine | EC 1.5.3.13, EC 1.5.3.17 | R09074 |
| N8-acetylspermidine | 4-acetamidobutanal | 1,3-diaminopropane | EC 1.5.3.15 | R09075 |
- ^ Salvi, Daniele; Tavladoraki, Paraskevi (2020-10-20). "The tree of life of polyamine oxidases". Scientific Reports. 10 (1): 17858. Bibcode:2020NatSR..1017858S. doi:10.1038/s41598-020-74708-3. ISSN 2045-2322. PMC 7576179. PMID 33082384.