Magnesium ions affect the quantitative but not the qualitative microsome mediated binding of benzo[alpha]-pyrene to DNA.

Five distinct hydrocarbon-deoxyribonucleoside adducts are separated by high pressure liquid chromatography after reaction of benzo[alpha]pyrene with calf thymus DNA in the presence of liver microsomes from 3-methylcholanthrene treated rats. The two major adducts co-chromatography with deoxyribonucleoside adducts obtained after hydrolysis of calf thymus DNA previously reacted with liver microsomal metabolically activated 9-hydroxy-benzo[alpha]pyrene or trans-7,8-dihydro-7,8-dihydroxybenzo[alpha]pyrene. High magnesium ion concentrations in the microsomal incubations cause a significant decrease in the covalent binding of the hydrocarbon to DNA but do not affect the qualitative distribution of the individual benzo[alpha]pyrene-deoxyribonucleoside adducts.