Glyphosate Is an Inhibitor of Plant Cytochrome P450: Functional Expression ofThlaspi arvensaeCytochrome P45071B1/Reductase Fusion Protein inEscherichia 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 forThlaspi arvensaeCYP71B1 inEscherichia coli.CYP71B1 was fused to the soluble domain of a plant cytochrome P450 reductase (CPR) fromCatharanthus 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 Ksof 60 μM was observed and an IC50of 12 μM was observed for glyphosate inhibition of CYP71B1 activity. The implications of these results are discussed.