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Not all P450-dependent reactions are monooxygenations, and not all monooxygenases are P450 enzymes (Mansuy and Renaud, 1995).
In particular, flavin monooxygenases or FMOs are NADPH-dependent enzymes that catalyze some reactions similar or identical to those catalyzed by P450 enzymes.
In mammalian species, FMOs are microsomal enzymes best known for their N- and S-oxidation activities (Ziegler, 2002).
Little is known about FMOs in insects. In the cinnabar moth Tyria jacobaea, a soluble FMO specifically N-oxidizes pyrolizidine alkaloids such as senecionine, seneciphylline, monocrotaline and axillarine (Lindigkeit et al., 1997, Naumann et al., 2002).
Only two FMO genes have been recognized in the Drosophila genome, and recombinant DmFMO-2 produced in E. coli is active in methimazole sulfoxidation assay (Scharf et al., 2004).
The Bombyx mori genome has three FMO genes (Sehlmeyer et al., 2010).
Langel and Ober 2011 reviewed the evolution of pyrrolizidine alkaloid N-oxygenases of adapted arctiid moths (Lepidoptera) showing that the enzymes originated by the duplication of a gene encoding an FMO of unknown function early in the arctiid lineage.
Tian et al., 2014 showed that metaflumizone toxicity in Spodoptera exigua resistant strains could be decreased by the FMO inhibitor methimazole as synergist. Tian et al. (2018) then cloned three FMOs from Spodoptera exigua , and functional expression in Sf9 cells with the baculovirus system showed that all three enzymes could metabolize metaflumizone and lambda-cyhalothrin.
A flavin-dependent monooxgenase confers resistance to chlorantraniliprole in the diamondback moth, Plutella xylostella (Mallott et al., 2019), where the gene PxFMO2 is constitutively overexpressed. Expression in transgenic Drosophila increases chloranthraniliprole tolerance in vivo.
Miyata et al. 2021 cloned three FMOs from the galling sawfly Pontania sp. . PonFMO1 when expressed in E.coli had extremely low activity in the conversion of Trp to indole acetaldoxime. (IAOx).
Wang et al., 2024 cloned 5 FMOs from Chilo suppressalis, of which two increase tolerance to chloranthraniliprole and spinetoram when expressed transgenically in Drosophila.
Wang et al. 2024 showed that Plutella xylostella PxFMO2 increased tolerance to emamectin benzoate and to chloranthraniliprole when expressed transgenically in Drosophila.