| Abstract
| - The lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK) is activated toreactive metabolites that methylate or pyridyloxobutylate DNA.Previous studies demonstratedthat pyridyloxobutylated DNA interferes with the repair ofO6-methylguanine (O6-mG)by O6-alkylguanine-DNA alkyltransferase (AGT). The AGT reactivity ofpyridyloxobutylated DNAwas attributed to (pyridyloxobutyl)guanine adducts. Onepotential AGT substrate adduct, 2‘-deoxy-O6-[4-oxo-4-(3-pyridyl)butyl]guanosine(O6-pobdG), was prepared. This adduct wasstableat pH 7.0 for greater than 13 days and to neutral thermal hydrolysisconditions (pH 7.0, 100°C, 30 min). Under mild acid hydrolysis conditions (0.1 N HCl,80 °C), O6-pobdG wasdepurinated to yieldO6-[4-oxo-4-(3-pyridyl)butyl]guanine(O6-pobG). O6-pobdGwas hydrolyzedto 4-hydroxy-1-(3-pyridyl)-1-butanone and guanine under strong acidhydrolysis conditions (0.8N HCl, 80 °C). O6-pobG was detected in0.1 N HCl hydrolysates of DNA alkylated with themodel pyridyloxobutylating agent4-(acetoxymethylnitrosamino)-1-(3-[5-3H]pyridyl)-1-butanone([5-3H]NNKOAc). When[5-3H]NNKOAc-treated DNA was incubated with eitherrat liver orrecombinant human AGT, O6-pobG was removed,presumably a result of transfer of thepyridyloxobutyl group from the O6-position ofguanine to AGT's active site.
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