Plant sterol 14 alpha-demethylase affinity for azole fungicides

Azole fungicides were thought to have much greater affinity for the fungal cytochrome P450 enzyme, sterol 14 alpha -demthylase (CYP51) than the plant orthologue. Using purified CYP51 from the plant Sorghum bicolor L Moenech, a direct comparison of the sensitivity to the fungicides triadimenol and te buconazole has been carried out. S. bicolor CYP51 was purified to homogenit y as determined by SDS-PAGE and specific heme content, Addition of the azol e fungicides triadimenol and tebuconazole induced type II spectral changes, with saturation occurring at equimolar azole/P450 concentrations. Inhibiti on of reconstituted activities revealed only a threefold insensitivity of t he plant CYP51 compared to a fungal CYP51, from the phytopathogen Ustilago maydis, as judged by IC50 values. The implications for fungicide mode of ac tion and application are discussed. (C) 2001 Academic Press.