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 lyophilized pyrimidine DNA constituents TMP, dCMP, CMP and dCyd was determined quantitatively in order to study explicitly the direct radiation effect.

MATERIALS AND METHODS

X-irradiation under an air or a nitrogen gas atmosphere and heavy ion bombardment in the beam vacuum were employed at 300 K. The release of free bases was investigated using HPLC and 1H-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 dose up to 360 kGy for X-irradiation or 200 kGy for heavy ion bombardment. The estimation of the radiation chemical yields revealed G values of 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 about one order of magnitude difference in yields between bases released and free radicals formed was found.

CONCLUSIONS

Compared with related 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 smaller.