FORMATION OF 4,4'-METHYLENE-BIS(2-CHLOROANILINE)-DNA ADDUCTS IN YEASTEXPRESSING RECOMBINANT CYTOCHROME P450S

N-Oxidation of 4,4'-methylene-bis(2-chloroaniline) (MBOCA) may lead to formation of DNA adducts. To determine if cytochrome P450s are involv ed in the formation of MBOCA derived-DNA adducts, yeast strains expres sing rodent P450s were exposed to MBOCA, and P-32-postlabelling of nuc leotides from yeast genomic DNA was done. Chromatographic analysis on PEI cellulose showed that, upon exposure to MBOCA for 1 h, nine DNA ad ducts were formed in yeast expressing phenobarbital-inducible rabbit P 450 2B5. With a 4-h-exposure, all adducts increased in parallel, In ce ll-free experiments, the incubation of MBOCA with phenobarbital-induce d rat microsomal fraction followed by incubation; with thymus DNA, led to the formation of more than ten DNA adducts. When yeast expressing 3-methylcholanthrene-inducible rat P450 1Al was exposed to MBOCA, one major and two minor adducts were formed. No adducts were detected in c ontrol yeast. These results show that recombinant rabbit P450 2B5 exhi bits a potential activation of MBOCA and that rat P450 1Al has some ef fect. The use of yeast expressing recombinant P450s and the technique of P-32-postlabelling facilitates a simple search for chemicals with c arcinogenic potential.