Isolation of microsomal cytochrome‐p450 isozymes fromUstilago maydisand their interaction with sterol demethylation inhibitors

摘要

AbstractA procedure for the isolation of microsomes containing cytochrome‐P450 isozymes fromUstilago maydisis described. Yields of P450 amount to approximately 19(±+ 6) pmol mg−1of microsomal protein. The wavelength of maximum absorbance of the reduced carbon monoxide difference spectrum is 448‐449 nm. The azole fungicides prochloraz, etaconazole, imazalil, triadimefon and 3‐(2,4‐dichlorophenyl)‐2‐(1H‐1,2,4‐triazol‐1‐yl)‐4(3H)‐quinazoline, which differ markedly in toxicity toU. maydis, all induce type II binding difference spectra at extremely low concentrations (10−9‐10−8M). The DMI concentrations which cause half saturation of type II binding difference spectra (IC50) do not correlate with the fungicidal activities of the azoles. Binding of carbon monoxide to ferrous cytochrome‐P450 was only slightly inhibited to different degrees by the DMIs tested. However, the inhibition of carbon monoxide binding also does not correlate with fungitoxicity of the DMIs. The results in this paper suggest that the spectrophotometric studies with this preparation are not useful for evaluating selective toxicity of D