DNA--benzo[a]pyrene adducts formed in a Salmonella typhimurium mutagenesis assay system.

The DNA adducts formed in Salmonella typhimurium when bacteria are incubated with radioactive benzo[a]pyrene and liver microsomal enzymes from several sources has been investigated. When enzyme preparations from Aroclor I254 or 3-methylcholanthrene induced C57BL/6N (B6) mice were used to mediate activation, the predominant product was an adduct between the 10 position of 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and the N-2 position of deoxyguanosine. Similar results were obtained with human liver and with Aroclor-induced rat-liver enzyme preparations. This adduct is also the major DNA product previously found when human tissues or certain rodent cells were incubated with benzo[a]pyrene. On the other hand, when activation of benzo[a]pyrene was mediated by a phenobarbital-induced B6 mouse-liver enzyme preparation, the extent of binding was quite low and the profile of DNA adducts in S. typhimurium DNA was quite different. Thus, under appropriate conditions, the activation and DNA binding of benzo[a]pyrene inthe microsome mediated S. typhimurium mutagenesis assay generally resembles that seen in intact mammalian cells. Caution must be exercised, however, in the choice of microsome-activation systems.