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 . 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.
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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. USA99 (2002) 6085–6090. [PMID: 11972041]