Scheme 3. Summary of Possible Metabolic Routes for B[a]P in Vivo^a.

^a Pathway A shows the formation of possible proximal epoxides (1) by cyt P450 followed by direct nucleophilic attack to form guanine adducts at the N2 position (2) or hydrolysis by epoxide hydrolase to form a diol product, and a second cyt P450-mediated epoxidation forming diol epoxides (3), and the final nucleophilic attack forming a guanine adduct at the N² position (4). Pathway B shows the one-electron oxidation by cyt P450 to form the reactive cation radical (5) with subsequent nucleophilic attack on guanine (6) or adenine (7) forming adducts at the N7 position on the nucleobases.