| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1986: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Radiation chemical reactivity of thymine, thymidine, and thymidine-5'-monophosphate in aqueous solution was mainly investigated to clarify the relationship between hydroxylation of DNA-base components and inactivation of biological cells by ionizing radiation. The action of additives on the radiation chemical reactions of these DNA-related compounds was also determined, comparing with that on the radiation inactivation of incubated cells. The results are summarized as follows.
1. The G-values for the radiation chemical decompositions in aqueous solution increases in the order of thymine < thymidine < thymidine-5'-monophosphate, but the respective increments are not so large. The increased radiation sensitivity by the bonding of deoxyribose and its phosphate to thymine is attributable to concurrence of the damage of 1-substituted side chains.
2. Oxygen promotes radiation-induced hydroxylation of thymine derivatives into glycols, while depresses their dihydrogenation. The cleavage of thymi
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ne-deoxyribose bond and the phosphoric acid release are enhanced by oxygen.
3. Glutathione as an intracellular protector depresses radiation-induced decomposition of thymine derivatives in the absence of oxygen. Glutathione captures hydroxyl radicals to inhibit the glycol formation and enhances the selectivity of the formation of dihydrothymine derivatives by the hydrogen donating action. Glutathione reacts with oxygen readily to give its oxidation form, thereby its radiation protecting activity being diminished.
4. Electron accepting compounds, stable radicals, electron donating compounds, and high-valent transition metal complexes promote radiation-induced hydroxylation of thymine under anoxic conditions, but many of them are inactive for thymidine and thymidine-5'-monophosphate bonding to deoxyribose.
5. There is a clear correlation between radiation inactivation of incubated cells and hydroxylation of nucleic acid bases, especially thymine into thymine glycol, in the radiation chemical system. Less
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