Department of Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Proc Natl Acad Sci U S A. 1982 Feb;79(3):744-8. doi: 10.1073/pnas.79.3.744.
Snake venom phosphodiesterase or endonuclease S1 digestion of neocarzinostatin chromophore-treated DNA, labeled in its thymidine residues, liberates an unusual labeled nucleoside from the 5' end of a drug-induced break. This substance, isolated by reverse-phase HPLC, possesses carbons from both the thymine and the deoxyribose moieties of thymidine in the DNA but, unlike thymidine, is readily degraded at pH 12 to thymine and a sugar fragment. The altered nucleoside was shown to contain a carbonyl group by its reduction with NaBH(4) to form a substance that has the chromatographic properties of thymidine and by its reaction with various hydrazines to form the respective hydrazone derivatives; the carbonyl exists as the 5' aldehyde as shown by its mild chemical oxidation to the carboxylic acid with simultaneous loss of the 5' (3)H. Mass spectral analysis showed a fragmentation pattern compatible with the structure thymidine-5'-aldehyde. These data indicate that the nonprotein chromophore of neocarzinostatin, in the presence of a reducing substance (2-mercaptoethanol) and molecular oxygen, selectively oxidizes the 5' carbon of nucleosides in DNA to the aldehyde, resulting in a strand break and a DNA fragment bearing nucleoside-5'-aldehyde at its 5' end.
蛇毒磷酸二酯酶或内切核酸酶 S1 消化新制癌菌素生色团处理的 DNA，标记其胸腺嘧啶残基，从药物诱导的断裂的 5' 端释放出一种不寻常的标记核苷。该物质通过反相 HPLC 分离，具有 DNA 中胸腺嘧啶和脱氧核糖部分的碳，但与胸腺嘧啶不同，在 pH 12 下易于降解为胸腺嘧啶和糖片段。通过其与 NaBH(4)的还原形成具有与胸腺嘧啶相同色谱性质的物质，以及通过其与各种肼的反应形成各自的腙衍生物，证明了改变的核苷含有羰基；羰基作为 5' 醛存在，如通过其与同时失去 5' (3)H 的温和化学氧化至羧酸所证明。质谱分析显示与结构胸腺嘧啶-5'-醛一致的碎片模式。这些数据表明，新制癌菌素的非蛋白生色团在还原物质（2-巯基乙醇）和分子氧存在下，选择性地将 DNA 中核苷的 5' 碳氧化为醛，导致链断裂和在其 5' 端带有核苷-5'-醛的 DNA 片段。
