An indentation of three fused benzene rings. A common bay region is the site on BENZO(A)PYRENE, an indirect carcinogen that is metabolically activated by the P-450 system at the 7,8-double bond, leading to a 7,8-oxide, which is rapidly converted to a 7,8-dihydrodiol and later epoxidated near the bay region at the 9,10-double bond. The resulting product, a diol-epoxide is a poor substrate for epoxide hydratase and is released from the mitochondria into the cell as a highly reactive electrophil, becoming an 'ultimate' carcinogen, as it reacts with negative charges in DNA. (From Segen, Dictionary of Modern Medicine, 1992).
