title: Black swallowtail (Papilio polyxenes) alleles encode cytochrome P450s that selectively metabolize linear furanocoumarins.
abstract: Cytochrome P450 monooxygenases are involved in metabolism of hostplant allelochemicals by larval Lepidoptera. Biochemical purification of the P450 polypeptide induced in Papilio polyxenes (black swallowtail) larvae in response to xanthotoxin, a linear furanocoumarin, has allowed us to clone cDNAs encoding two allelic variants of the CYP6B1 locus. Expression of these alleles in lepidopteran cell lines using baculovirus expression vectors has demonstrated that both P450 isoforms metabolize substantial amounts of linear furanocoumarins, such as xanthotoxin and bergapten, but not angular furanocoumarins, such as angelicin and sphondin. These linear furanocoumarins are ubiquitous constituents of the hostplants of P. polyxenes. The efficiency of linear furanocoumarin metabolism is strongly affected by the nature of the substituents on the benzene ring; methoxy-derivatives are metabolized more efficiently than are derivatives with smaller (hydroxy-) or larger (8-O isopentenyl) groups. Metabolism of either bergapten or xanthotoxin is inhibited in the presence of the other. In addition, metabolism of linear furanocoumarins is inhibited by the presence of nonmetabolizable angular furanocoumarins, indicating that the active site of CYP6B1 binds angular furanocoumarins. The reactivities described here indicate that P. polyxenes larvae express at least two selective furanocoumarin-metabolic P450s: CYP6B1, which metabolizes a discrete set of linear furanocoumarins, and another P450, as yet unidentified, which metabolizes angular furanocoumarins more efficiently than does CYP6B1.
authors.affiliation: Department of Entomology, University of Illinois, Urbana 61801.
authors.forename: R
authors.initials: R
authors.lastname: Ma
authors.forename: M B
authors.initials: MB
authors.lastname: Cohen
authors.forename: M R
authors.initials: MR
authors.lastname: Berenbaum
authors.forename: M A
authors.initials: MA
authors.lastname: Schuler
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002080:Butterflies / Q000201:enzymology* / Q000235:genetics*; D002460:Cell Line; D003374:Coumarins / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004790:Enzyme Induction; D014644:Genetic Variation; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D007814:Larva; D008730:Methoxsalen / Q000494:pharmacology; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009036:Moths; D016133:Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection
chemical_list: D003374:Coumarins; D007527:Isoenzymes; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C022657:steroid hormone 6-beta-hydroxylase; D008730:Methoxsalen