Interaction of microsomal cytochrome P-450 isolated from Aspergillus fumigatus with fluconazole and itraconazole.
A simple procedure has been developed for isolating a microsomal fraction from Aspergillus fumigatus which contains cytochrome P-450. Maximum absorbance of the carbon monoxide/ferrous cytochrome P-450 difference spectrum was at a wavelength of 451 nm. The triazole antifungal agents, fluconazole and itraconazole, produced type II binding difference spectra with ferric cytochrome P-450 in A. fumigatus microsomes and an azole concentration of 0.5 microM was sufficient to saturate the spectroscopic response when the cytochrome P-450 concentration was 0.07 microM. This extremely high affinity binding precluded the determination of apparent dissociation constants for the cytochrome P-450-azole complexes. Itraconazole was found to have a marginally greater affinity for cytochrome P-450 than fluconazole, as determined from a comparison of their potential to reduce the rate of binding of carbon monoxide to the ferrous haemoprotein. The high affinity binding of both compounds to the cytochrome P-450 from A. fumigatus is consistent with their proposed antifungal mode of action through inhibition of the sterol 14 alpha-demethylase cytochrome P-450 required for ergosterol biosynthesis.
Ballard
S A
SA
Department of Discovery Biology, Pfizer Central Research, Sandwich, Kent, UK.
Kelly
S L
SL
Ellis
S W
SW
Troke
P F
PF
D000935:Antifungal Agents / Q000378:metabolism*; D001232:Aspergillus fumigatus / Q000648:ultrastructure*; D001667:Binding, Competitive; D002248:Carbon Monoxide / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D015725:Fluconazole / Q000378:metabolism*; D017964:Itraconazole; D007654:Ketoconazole / Q000031:analogs & derivatives* / Q000378:metabolism; D008861:Microsomes / Q000737:chemistry; D013053:Spectrophotometry
D000935:Antifungal Agents; D017964:Itraconazole; D002248:Carbon Monoxide; D015725:Fluconazole; D003577:Cytochrome P-450 Enzyme System; D007654:Ketoconazole