Detection of Guanine‐C8‐2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine Adduct as a Single Spot on Thin‐layer Chromatography by Modification of the (32)P‐Postlabeling Method

N‐(Deoxyguanosin‐8‐yl)‐2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (dG‐C8‐PhIP) has been shown to be a major adduct in DNA of rats given [(3)H]PhIP. However, when DNA from organs of rats fed PhIP was analyzed by the (32)P‐postlabeling method under standard and adduct‐intensification conditions, four adduct spots were observed, and 3′,5′‐pdGp‐C8‐PhIP was detected as a minor, not a major, adduct spot. Since the three other major adduct spots were suspected to be those of adducted di‐ or oligo‐nucleotides, the (32)P‐labeled samples were further treated with nuclease PI and phosphodiesterase I and found to yield only a single adduct spot. The material in this adduct spot was confirmed to be 5′‐pdG‐C8‐PhIP, Thus, using this newly modified (32)P‐postlabeling method, dG‐C8‐PhIP was detected as a major adduct in DNA of rats given PhIP.