Sequence of Events in the Process of Radiation Damage in a Nucleic Acid Constituent

Abstract

Thermoluminescence and electron spin resonance studies of adenine, D-ribose, adenosine, adenylic acids and polyadenylic acid have shown that, after irradiation at 77°k, the energy is localized on the heterocyclic base molecule and a single symmetrical E.S.R. line has been observed in all samples except D-ribose, which shows a triplet. On warming to room temperature, the E.S.R. spectra from all the samples are changed and resemble that of D-ribose, suggesting a migration of damage to the sugar molecule. It is seen that the addition of sugar and sugar phosphate moieties affects the yield of free radicals at 77°k. In the presence of cysteamine, an asymmetrical E.S.R. signal is observed at 77°k, and the asymmetry at the low-field side of the main spectrum arises due to a line associated with the sulphur atom. All the samples emit light during the period of their warming to room temperature, and the maximum glow occurs at − 170°c. The intensity of light emitted is maximal in the base as compared with that from nucleoside and the nucleotide. All the samples show ultra-violet phosphorescence in the region 3700–6000 Å, and the presence of cysteamine quenches phosphorescence as well as thermoluminescence.