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 physicochemical effects induced by γ and α radiation on the thermal denaturation dynamics of native macromolecular calf thymus DNA, combining dielectric relaxation spectroscopy (DRS) and UV thermal transition spectrophotometry (TTS), while the apparent molecular weight (MW) distribution of the DNA macromolecules was measured by pulse field gel electrophoresis (PFGE). A DNA thermal stability enhancement over the non-irradiated samples was observed at radiation doses <10 Gy for γ rays and 32 Gy for α particles, attributed to the development of intra and/or intermolecular DNA-DNA interactions, whereas at higher irradiation doses, the expected decrease of thermal stability was observed. Moreover, in all studied cases, the recorded conductivity changes were found to precede by 2 to 3°C those of UV TTS absorbance changes, a fact indicative of a multi-stage process for DNA thermal transition. Finally, the displacement of the low dose region limit towards higher doses in the case of α particles, confirm earlier results attesting higher yields of DNA strand breaks induced by γ rays compared to α particles