Characterization of pig liver purified cytochrome P-450 isoenzymes for ochratoxin A metabolism studies.

In this paper, we report the characterization of 4 isolated, constitutive cytochrome P-450 fractions from pig liver microsomes. The two predominant forms, A2 and A3, exhibit several similarities: a Mr of 54 kDa, a lambda max CO-Fe++ at 448 nm, a relatively high ratio of the high-spin form and an immunological cross-reaction with polyclonal antibodies against rat liver P-450 IIB1. It is shown that these forms and the minor form Ba, which are active as benzphetamine N-demethylase, play an important metabolic role in ochratoxin A oxidation. This mycotoxin was oxidized by at least 3 different pig liver cytochrome P-450 fractions, each producing different metabolites, namely (4R)-, (4S)-hydroxyochratoxin A, and a new lipophilic metabolite. Since the pig is particularly susceptible to ochratoxin A toxicity, it represents a good animal model for in vitro studies of the metabolism of such a xenobiotic.

Sulphoxidation of albendazole by the FAD-containing and cytochrome P-450 dependent mono-oxygenases from pig liver microsomes.

1. Two distinct microsomal pathways involved in the metabolism of albendazole (ABZ) to albendazole-sulphoxide (SO.ABZ) by pig liver microsomes have been identified and quantified. 2. The binding of ABZ to microsomal cytochrome P-450 (Type I spectrum, Ks = 25.5 microM), the decrease of the rate of sulphoxidation by antibody against NADPH cytochrome c reductase, and the use of purified cytochrome P-450 A demonstrated the contribution of a cytochrome P-450-dependent mono-oxygenase to the metabolism of ABZ. 3. The involvement of FAD-containing mono-oxygenase (FMO) was shown by thermal pretreatment of microsomes, n-octylamine activation of the reaction, and by using purified pig liver FMO. 4. From Km and Vmax values, it would appear that the relative contributions of the two systems depend on the concentration of ABZ.