Metabolism of myristicin by Depressaria pastinacella CYP6AB3v2 and inhibition by its metabolite

Abstract

Although methylenedioxyphenyl (MDP) compounds, such as myristicin, are useful in the management of insecticide-resistant insects, the molecular mechanisms for their action in mammals and insects have not been elucidated. In this study, GC–MS analyses of methanol extracts of foliage of wild parsnip ( Pastinaca sativa) have identified myristicin as a substrate for CYP6AB3v2, an imperatorin-metabolizing cytochrome P450 monooxygenase from Depressaria pastinacella (parsnip webworm). In contrast with its strong inhibitory effects on many mammalian P450s, myristicin is effectively metabolized by CYP6AB3v2 ( V max and K m of 97.9 pmol/min/pmol P450 and 17.9 μM, respectively) at a rate exceeding that recorded previously for imperatorin, the only other known substrate for this highly specialized enzyme. The myristicin metabolite of CYP6AB3v2 is 1-(3′,4′-methylenedioxy-5′-methoxyphenyl)-2,3-epoxypropane. Molecular dockings have indicated that, unlike other epoxide metabolites of furanocoumarins, this epoxide metabolite is likely to remain in the CYP6AB3v2 catalytic site due to its low binding energy (−31.0 kcal/mol). Inhibition assays indicate that myristicin acts as a mixed inhibitor of this insect P450 and suggest that the epoxide metabolite may be an intermediate involved in the formation of P450–methylenedioxyphenyl complexes.