Matijasevic Z, Sekiguchi M, Ludlum D B
Department of Pharmacology, University of Massachusetts Medical School, Worcester 01655.
Proc Natl Acad Sci U S A. 1992 Oct 1;89(19):9331-4. doi: 10.1073/pnas.89.19.9331.
The human carcinogen vinyl chloride is metabolized in the liver to reactive intermediates which form N2,3-ethenoguanine in DNA. N2,3-Ethenoguanine is known to cause G----A transitions during DNA replication in Escherichia coli, and its formation may be a carcinogenic event in higher organisms. To investigate the repair of N2,3-ethenoguanine, we have prepared an N2,3-etheno[14C]guanine-containing DNA substrate by nick-translating DNA with [14C]dGTP and modifying the product with chloroacetaldehyde. E. coli 3-methyladenine DNA glycosylase II, purified from cells which carry the plasmid pYN1000, releases N2,3-ethenoguanine from chloroacetaldehyde-modified DNA in a protein- and time-dependent manner. This finding widens the known substrate specificity of glycosylase II to include a modified base which may be associated with the carcinogenic process. Similar enzymatic activity in eukaryotic cell might protect them from exposure to metabolites of vinyl chloride.
人类致癌物氯乙烯在肝脏中代谢为活性中间体，这些中间体在DNA中形成N2,3-乙烯基鸟嘌呤。已知N2,3-乙烯基鸟嘌呤在大肠杆菌DNA复制过程中会导致G----A转换，其形成可能是高等生物中的致癌事件。为了研究N2,3-乙烯基鸟嘌呤的修复，我们通过用[14C]dGTP对DNA进行缺口平移并用氯乙醛修饰产物，制备了含N2,3-乙烯基[14C]鸟嘌呤的DNA底物。从携带质粒pYN1000的细胞中纯化的大肠杆菌3-甲基腺嘌呤DNA糖基化酶II以蛋白质和时间依赖性方式从氯乙醛修饰的DNA中释放N2,3-乙烯基鸟嘌呤。这一发现拓宽了已知的糖基化酶II的底物特异性，使其包括一种可能与致癌过程相关的修饰碱基。真核细胞中类似的酶活性可能保护它们免受氯乙烯代谢产物的影响。
