Chemical Effects of Ionizing Radiation on Deoxyribonucleic Acid in Dilute Aqueous Solution

Abstract

WHEN purine and pyrimidine nucleotides in dilute aqueous solution are irradiated with ionizing radiation they are destroyed by two pathways¹. The minor pathway is attack upon the sugar moiety followed by release of free base¹. Details of the mode of sugar attack have not been established; but possible reactions have been suggested by Daniels et al. ². The major pathway is attack of the base moiety which with purines in the absence of oxygen yields the corresponding formamido-pyrimidine nucleotide³. When pyrimidine nucleotides are irradiated in the absence of oxygen sugar phosphate is liberated, but there is no ultra-violet absorbing product arising from base attack. When oxygen is present during irradiation G-values (molecules per 100 eV.) for nucleotide destruction are increased 2–3 times⁴. For purine nucleotides the increased degradation in oxygen is almost entirely an augmented base attack, but no ultra-violet product arising from it is found⁴. When pyrimidines are irradiated in the presence of oxygen hydroxy-hydroperoxides are formed⁵. G-values for destruction of pyrimidines in the presence of oxygen are greater than those for purines^1,6 and suggest that when deoxyribonucleic acid is irradiated pyrimidines will be destroyed to a greater extent. Extrapolation of the effects of radiation upon nucleotides to effects upon deoxyribonucleic acid is complicated in an uncertain way by the influence of inter-nucleotide linkages and hydrogen bonding of base pairs. This communication reports the amounts of base and sugar destroyed when aqueous solutions of calf thymus deoxyribonucleic acid are irradiated.