The role of highly purified cytochrome P-450 isozymes in the activation of 4-aminobiphenyl to mutagenic products in the Ames test.

The role of cytochromes P-450 and P-447 in the activation of 4-aminobiphenyl to mutagens in the Ames test was studied using S9 preparations and highly purified isozymes. S9 preparations from beta-naphthoflavone-pretreated rats were more efficient in converting 4-aminobiphenyl to mutagens than the corresponding preparations from phenobarbitone-pretreated animals. Similarly, reconstituted systems comprising purified cytochrome P-447 were twice as efficient as cytochrome P-450 in activating the carcinogen. Of all the known Phase I metabolites of 4-aminobiphenyl, only the N-hydroxy-derivative was mutagenic in the Ames test. These findings indicate that arylamine N-hydroxylase is a cytochrome P-450 dependent enzyme, and the nature of the isozyme of the cytochrome is an important determinant of its mutagenicity.