Dielectric and UV spectrophotometric study of physicochemical effects of ionizing radiation on mammalian macromolecular DNA

The purpose of this work was the comparative investigation of physicochemic al effects induced by gamma and alpha radiation on the thermal denaturation dynamics of native macromolecular calf thymus DNA, combining dielectric re laxation spectroscopy (DRS) and vv thermal transition spectrophotometry (TT S), while the apparent molecular weight (Mw) distribution of the DNA macrom olecules was measured by pulse field gel electrophoresis (PFGE). A DNA ther mal stability enhancement over the non-irradiated samples was observed at r adiation doses < 10 Gy for gamma rays and 32 Gy for alpha particles, attrib uted to the development of intra and/or intermolecular DNA-DNA interactions , whereas at higher irradiation doses, the expected decrease of thermal sta bility was observed. Moreover, in all studied cases, the recorded conductiv ity changes were found to precede by 2 to 3 degreesC those of UV TTS absorb ance changes, a fact indicative of a multi-stage process for DNA thermal tr ansition. Finally, the displacement of the low dose region limit towards hi gher doses in the case of alpha particles, confirm earlier results attestin g higher yields of DNA strand breaks induced by gamma rays compared to alph a particles.