title: Glyphosate is an inhibitor of plant cytochrome P450: functional expression of Thlaspi arvensae cytochrome P45071B1/reductase fusion protein in Escherichia coli.
abstract: Glyphosate (Roundup) is an herbicide used extensively worldwide which acts as an inhibitor of 5'enolpyruvylshikimate-3-phosphate synthase and for which transgenic herbicide resistant plants have been developed. Here we report for the first time that glyphosate is an inhibitor of cytochrome P450 using a functional expression system for Thlaspi arvensae CYP71B1 in Escherichia coli. CYP71B1 was fused to the soluble domain of a plant cytochrome P450 reductase (CPR) from Catharanthus roseus. CYP71B1 could obtain reducing equivalents in this fusion construct and metabolised the polycyclic aromatic hydrocarbon, benzo(a)pyrene. The fusion protein retained normal spectral characteristics having a Soret peak at 448 nm in the reduced carbon monoxide difference spectrum. Addition of the herbicide resulted in a Type II spectrum indicative of binding via the nitrogen group to haem as a sixth ligand. A Ks of 60 microM was observed and an IC50 of 12 microM was observed for glyphosate inhibition of CYP71B1 activity. The implications of these results are discussed.
authors.affiliation: Institute of Biological Sciences, University of Wales Aberystwyth, United Kingdom.
authors.forename: D C
authors.initials: DC
authors.lastname: Lamb
authors.forename: D E
authors.initials: DE
authors.lastname: Kelly
authors.forename: S Z
authors.initials: SZ
authors.lastname: Hanley
authors.forename: Z
authors.initials: Z
authors.lastname: Mehmood
authors.forename: S L
authors.initials: SL
authors.lastname: Kelly
mesh_terms: D001564:Benzo(a)pyrene / Q000378:metabolism; D001665:Binding Sites / Q000187:drug effects; D002384:Catalysis / Q000187:drug effects; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006540:Herbicides / Q000494:pharmacology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000037:antagonists & inhibitors* / Q000138:chemical synthesis / Q000378:metabolism; D010940:Plant Proteins / Q000037:antagonists & inhibitors* / Q000138:chemical synthesis / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors* / Q000138:chemical synthesis / Q000378:metabolism; D013379:Substrate Specificity; D000097797:Glyphosate
chemical_list: D001564:Benzo(a)pyrene; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System; D005998:Glycine; D006540:Herbicides; D009251:NADPH-Ferrihemoprotein Reductase; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D000097797:Glyphosate