A novel electrophoretic pattern of induction of rat liver microsomal membrane polypeptides by 2-acetylaminofluorene, nitrosamine and azo dye administration

The electrophoretic patterns of the polypeptides of the microsomal membrane fraction of the livers of rats treated with various agents were compared. Administration of phenobarbital, or of benzo[a]pyrene or 3-methylcholanthrene, resulted in specific increases of membrane polypeptides corresponding to cytochrome P-450 and cytochrome P-448 species respectively. Administration of 2-acetylaminofluorene, diethylnitrosamine, dimethylnitrosamine, N,N-dimethyl-4-aminoazobenzene or 3′-methyl-N,N-dimethyl-4-aminoazobenzene resulted in a marked increase of 2 other polypeptides, migrating just ahead of the phenobarbital-responsive cytochrome P-450 species. Preliminary evidence suggests that at least one of these 2 polypeptides may contain heme. The results indicate that administration of these N-containing carcinogens to rats results in a common electrophoretic pattern of induction of 2 specific microsomal membrane polypeptides. This pattern is different from those observed with classical inducers of the rat liver mixed-function oxidase system.