The Release of 5-Methylene-2-Furanone From Irradiated DNA Catalyzed by Cationic Polyamines and Divalent Metal Cations

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Release of 5-methylene-2-furanone (5-MF), a characteristic marker of DNA deoxyribose oxidative damage at the C1′ position, was observed in significant quantities from X-irradiated DNA. This observation, which held for DNA irradiated either in aqueous solution or as a film, requires postirradiation treatment at 90°C in the presence of polyamines and divalent metal cations at biological pH. The 5-MF product was quantified by using reverse-phase HPLC. The radiation chemical yield of 5-MF comprised more than 30% of the yield of total unaltered base release. Polylysine, spermine and Be(II) showed the strongest catalytic effect on 5-MF release, while Zn(II), Cu(II), Ni(II), putrescine and Mg(II) were substantially less efficient. We have hypothesized that the 5-MF release from irradiated DNA occurs through catalytic decomposition of the 2′-deoxyribonolactone (dL) precursor through two consecutive β- and δ-phosphate elimination reactions. A stepwise character of the process was indicated by the S-shaped time course of 5-MF accumulation. If dL proves to be the precursor to 5-MF formation, it would then follow that dL is a very important lesion generated in DNA by ionizing radiation.