RELEASE OF UNALTERED BASES FROM POLYCRYSTALLINE PYRIMIDINE DNA CONSTITUENTS AFTER X-IRRADIATION AND BOMBARDMENT WITH HEAVY-IONS

Purpose: The radiation-induced release of unaltered bases from the lyo philized pyrimidine DNA constituents TMP, dCMP, CMP and dCyd was deter mined quantitatively in order to study explicitly the direct radiation effect. Materials and methods: X-irradiation under an air or a nitrog en gas atmosphere and heavy ion bombardment in the beam vacuum were em ployed at 300 K. The release of free bases was investigated using HPLC and H-1-NMR. Dose-yield curves for free radicals of X-irradiated TMP and dCMP samples were determined by EPR spectroscopy. Results: As one of the main products, the release of unaltered bases is linear with do se up to 360 kGy for X-irradiation or 200 kGy for heavy ion bombardmen t. The estimation of the radiation chemical yields revealed G values o f about 10(-7) mol J(-1). The heavy ion bombardment and X-irradiation under nitrogen effected a lower yield for base release than that for X -irradiation under air. For X-irradiation at sufficiently high doses a bout one order of magnitude difference in yields between bases release d and free radicals formed was found. Conclusions: Compared with relat ed findings as described in the literature, the G values from DNA are in the same order of magnitude, but from nucleosides in frozen aqueous solutions the yields of free bases are several orders of magnitude sm aller.