Products from polycrystalline DNA constituents after X-irradiation and heavy-ion bombardment: Formation of the 5,6-dihydroadduct in thymidine 5'-monophosphate and release of unaltered bases in nucleotides

Abstract

Purpose : The major products from polycrystalline purine and pyrimidine DNA nucleotides after low- and high-LET irradiation were investigated quantitatively by HPLC and 1H-NMR spectroscopy. Materials and methods : Solid nucleotide samples were either X-irradiated as cylindrical pellets or heavy-ion bombarded (LET range of 100-12500keV/ μ m) as very thin tablets at 300K. Product analysis was performed by HPLC and 1H-NMR. Results : For TMP the 5,6-dihydroadduct was found to be formed as product of electron reaction. In addition, all four DNA nucleotides showed a radiation-induced base release, which is probably connected with the oxidative radiation action. The formation of the products was linear with dose up to 300 kGy for X-irradiation or 200kGy for heavy-ion bombardment. The estimation of the radiation chemical yields revealed G-values of about 10 -7 molJ -1 and were typically smaller for irradiation with charged particles than those for X-rays. After heavy-ion bombardment the G-values first increased with increasing LET and decreased for very heavy ions. Conclusions : The yields for base release from both purine and pyrimidine nucleotides are comparable in magnitude. The 5,6-dihydroadduct from TMP is a major radiation induced product with larger yields than found for base release after X-irradiation and comparable yields after heavy-ion bombardment. The LET dependence of the G-values for base release in nucleotides is similar and resembles the double strand break formation in DNA. The observed similarity in the LET dependence of the G-values might derive from an inhomogeneous distribution of energy deposition resulting in 'clustered damage'.