II. The “After-Effect” of Irradiation of Deoxyribonucleic Acid in Oxygenated Solutions

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Abstract
Experiments have been carried out to attempt to establish the nature of the after-effect of X irradiation on deoxyribonucleic acid in oxygen. The change which occurs during 48 hours after the cessation of the radiation is followed by means of viscosity measurements. Very little after-effect is observed when oxygen is absent, and the explanation of the effect is accordingly sought by considering the effects of the agents (e.g. the radical O2H and also molecular H2O2) produced characteristically in the irradiation of oxygenated aqueous solutions. It is concluded that the effect observed can mainly be accounted for by both the formation of unstable peroxidic intermediates and also the action of hydrogen peroxide, formed during the irradiation, acting on nucleic acid damaged by other radicals (e.g. H, OH and O2H) formed during the irradiation. Experiments on the effect of various protective agents provide indirect evidence in support of this view.