Binding of azole fungicides related to diclobutrazol to cytochrome P‐450

Fungicides containing the imidazole and triazole groups are known to block the 14α‐demethylation reaction in ergosterol biosynthesis, which is a cytochrome P‐450 enzyme system. Fungicides related to diclobutrazol [(2RS, 3RS)‐1‐(2,4‐dichlorophenyl)‐4,4‐dimethyl‐2‐(1,2,4‐triazol‐1‐yl)pentan‐3‐ol] bind to cytochrome P‐450 in rat liver microsomes, whole yeast cells, yeast microsomes and to a partially purified cytochrome P‐450 from yeast, with Type II spectral changes. The most fungicidally active isomer (2R, 3R) shows greater binding than the less active (2S, 3S)‐enantiomer to yeast microsomes; when the cytochrome P‐450 was purified, a preparation was obtained to which binding more closely matched the fungicidal activity. Binding to rat liver microsomes does not reflect the fungicidal activity of the compounds.