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, A 2 and A 3, exhibit several similarities; a M r of 54 kDa, a λ 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 (4 R)-, (4 S)-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.