The effects of cytochrome P-450-448 inhibitors on the binding of benzo(a)pyrene and derivatives to DNA upon microsomal activation.

1. [3H]Benzo(a)pyrene and 6-substituted derivatives of [3H]benzo(a)pyrene are covalently bound to calf thymus DNA upon reaction with microsomal preparations from rats pretreated with 3-methylcholanthrene in the presence of NADPH. Two different types of cytochrome P-450-448 inhibitors, alpha-naphthoflavone and 1-benzylimidazole, show greater than 80% inhibition of the binding of benzo(a)pyrene to DNA. 2. In the presence of these inhibitors, 6-hydroxymethylbenzo(a)pyrene, 6-methylbenzo(a)pyrene and 6-formylbenzo(a)pyrene show varying degrees of inhibition of binding to DNA depending upon the inhibitor employed. 3. Polyguanylic acid is the most effective substrate for the binding of each activated polynuclear aromatic hydrocarbon; polyadenylic acid and DNA show essentially equivalent binding.