Reaction: sym-homospermidine + 2 O2 + H2O = 1-formylpyrrolizidine + 2 H2O2 + 2 NH3 (overall reaction)
(1a) sym-homospermidine + O2 = N-(4-aminobutylpyrrolinium) ion + H2O2 + NH3
(1b) N-(4-aminobutylpyrrolinium) ion + O2 + H2O = N-(4-oxobutylpyrrolinium) ion + NH3 + H2O2
(1c) N-(4-oxobutylpyrrolinium) ion = 1-formylpyrrolizidine (spontaneous)
Glossary: (-)-trachelanthamidine = (1R,7aS)-hexahydro-1H-pyrrolizin-1-ylmethanol
Other name(s): HSO
Systematic name: homospermidine:oxygen oxidase (deaminating, cyclizing)
Comments: The copper-containing enzyme has been isolated from the plant Heliotropium indicum. It is involved in the biosynthesis of the pyrrolizidine alkaloid (-)-trachelanthamidine which acts as a secondary metabolite for the defense against herbivores. The oxidation of sym-homospermidine proceeds in three steps and results in a cyclization.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
References:
1. Zakaria, M.M., Stegemann, T., Sievert, C., Kruse, L.H., Kaltenegger, E., Girreser, U., Cicek, S.S., Nimtz, M. and Ober, D. Insights into polyamine metabolism: homospermidine is double-oxidized in two discrete steps by a single copper-containing amine oxidase in pyrrolizidine alkaloid biosynthesis. Plant Cell 34 (2022) 2364-2382. [PMID: 35212762]