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 32P-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 [3H]PhIP. However, when DNA from organs of rats fed PhIP was analyzed by the 32P-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 32P-labeled samples were further treated with nuclease P1 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 32P-postlabeling method, dG-C8-PhIP was detected as a major adduct in DNA of rats given PhIP.