Identification of thymidine-5′-aldehyde at DNA strand breaks induced by neocarzinostatin chromophore

Publisher Website
Google Scholar
Abstract
Snake venom phosphodiesterase or endonuclease S1 digestion of neocarzinostatin chromophore-treated [calf thymus] DNA, labeled in its thymidine residues, liberated an unusual labeled nucleoside from the 5'' end of a drug-induced break. This substance, isolated by reverse-phase HPLC [high pressure liquid chromatography], possessed carbons from the thymine and the deoxyribose moieties of thymidine in the DNA, but, unlike thymidine, was readily degraded at pH 12 to thymine and a sugar fragment. The altered nucleoside was shown to contained a carbonyl group by its reduction with NaBH4 to form a substance that had the chromatographic properties of thymidine and by its reaction with various hydrazines to form the respective hydrazone derivatives; the carbonyl existed as the 5'' aldehyde as shown by its mild chemical oxidation to the carboxylic acid with simultaneous loss of the 5'' 3H. Mass spectral analysis showed a fragmentation pattern compatible with the structure thymidine-5''-aldehyde. Apparently 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. [Neocarzinostatin is an antineoplastic drug.].