Specificity of rat liver cytochrome P-450 isozymes in the mutagenic activation of benzo[a]pyrene, aromatic amines and aflatoxin B1.

The ability of three purified forms of rat liver cytochrome P-450 to metabolically activate benzo[a]pyrene, trans-benzo-[a]pyrene-7,8-dihydrodiol, 2-aminofluorene, aflatoxin B1, dimethylnitrosamine, and a pyrolysis product of tryptophan(3-amino-1-methyl-5H-pyrido(4,3-b)indole) (Trp-P-2) to mutagenic products was examined using Salmonella typhimurium strains TA98 and G46 in a reconstituted monooxygenase system. The isozymes examined were cytochrome P-450-PB (the major phenobarbital inducible form), and the two major 3-MC inducible forms (cytochromes P-448(52) and P-448(55)). Cytochromes P-448(52) and P-448(55) preferentially metabolize 2-aminofluorene and Trp-P-2 to mutagenic products. However, only cytochrome P-448(55) metabolizes benzo[a]pyrene and its 7,8-dihydrodiol derivative to mutagenic products. Both cytochrome P-448(52) and P-448(55) metabolize aflatoxin B1 to mutagenic products at a much faster rate than cytochrome P-450-PB. Dimethylnitrosamine was not activated by any of the isozymes tested.