Immunological and enzymatic comparison of hepatic cytochrome P-450 fractions from phenobarbital-, 3-methylcholanthrene-, beta-naphthoflavone- and 2,3,7,8- tetrachlorodibenzo-p-dioxin-treated rats

Abstract

A comparison of the cytochrome P-450 forms induced in rat liver microsomes by phenobarbital on the one hand, and 3-methylcholanthrene, beta-naphthoflavone and 2,3,7,8-tetrachlorodibenzo-p-dioxin on the other hand, was performed using specific antibodies: anti-P-450 B2 PB IG (against the phenobarbital-induced cytochrome P-450) and anti-P-450 B2 BNF IG (against the beta-naphthoflavone-induced cytochrome P-450). On DEAE-cellulose chromatography, four cytochrome P-450 fractions were separated, called P-450 A (non-adsorbed), P-450 Ba, P-450 Bb and P-450 Bc, from control, phenobarbital-, 3-methylcholanthrene, beta-naphthoflavone- and 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated rats. Cytochrome P-450 A fractions appeared to be unmodified by the inducers, whereas the specifically induced cytochrome P-450 forms were always recovered in Bb fractions. The P-450 Bb fractions induced by 3-methylcholanthrene, beta-naphthoflavone and 2,3,7,8-tetrachlorodibenzo-p-dioxin exhibited common antigenic determinants, comparable catalytic activities (benzphetamine N-demethylase, benzo[a]pyrene hydroxylase) and similar mol. wts. Moreover, the inhibition patterns by the two antibodies of benzphetamine N-demethylase and benzo[a]pyrene hydroxylase activities catalysed by 3-methylcholanthrene, beta-naphthoflavone and 2,3,7,8-tetrachlorodibenzo-p-dioxin microsomes or by the corresponding P-450 Bb fractions in a reconstituted system were quite identical. By these different criteria, beta-naphthoflavone, 3-methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin seem to induce a common cytochrome P-450 species in rat liver.