The Enzyme Database

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Accepted name: senecionine N-oxygenase
Reaction: senecionine + NADPH + H+ + O2 = senecionine N-oxide + NADP+ + H2O
Other name(s): senecionine monooxygenase (N-oxide-forming); SNO
Systematic name: senecionine,NADPH:oxygen oxidoreductase (N-oxide-forming)
Comments: A flavoprotein. NADH cannot replace NADPH. While pyrrolizidine alkaloids of the senecionine and monocrotaline types are generally good substrates (e.g. senecionine, retrorsine and monocrotaline), the enzyme does not use ester alkaloids lacking an hydroxy group at C-7 (e.g. supinine and phalaenopsine), 1,2-dihydro-alkaloids (e.g. sarracine) or unesterified necine bases (e.g. senkirkine) as substrates [1]. Senecionine N-oxide is used by insects as a chemical defense: senecionine N-oxide is non-toxic, but it is bioactivated to a toxic form by the action of cytochrome P-450 oxidase when absorbed by insectivores.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 220581-68-0
1.  Lindigkeit, R., Biller, A., Buch, M., Schiebel, H.M., Boppre, M. and Hartmann, T. The two facies of pyrrolizidine alkaloids: the role of the tertiary amine and its N-oxide in chemical defense of insects with acquired plant alkaloids. Eur. J. Biochem. 245 (1997) 626–636. [DOI] [PMID: 9182998]
2.  Naumann, C., Hartmann, T. and Ober, D. Evolutionary recruitment of a flavin-dependent monooxygenase for the detoxification of host plant-acquired pyrrolizidine alkaloids in the alkaloid-defended arctiid moth Tyria jacobaeae. Proc. Natl. Acad. Sci. USA 99 (2002) 6085–6090. [DOI] [PMID: 11972041]
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