Dielectric changes precede hydrogen bond breakage during helix to coil transition of deoxyribonucleic acid

An interesting and simultaneously unexpected thermodynamic stability of the DNA helix was observed when studying the effects of exposure to /spl gamma/- and /spl alpha/-irradiation on the double helix to coil thermal transition phase of mammalian macromolecular DNA. The results show that at the low dose range, of 0 to 12 Gy, which is of importance for radiation biology and where the effects of exposure to ionizing radiation were not explored in the previously published work, an increase of the dose of ionizing radiation results in an increase of the thermodynamic stability as well as in an increase of the apparent molecular weight of the DNA macromolecules. In all cases conductivity changes precede by a /spl Delta/T of about 3/spl deg/C the helix to coil transition changes, as those are measured by the breakage of the intramolecular hydrogen bonds. This /spl Delta/T is independent of the effected molecular weight changes.