Abstract
The effects on deoxyribonucleic acid (DNA) and simple model substances of irradiation with ultra-violet and near ultra-violet light have been studied in the presence of hydrogen peroxide at various concentrations in glass and quartz tubes. It is found that the rate of loss of the viscosity agrees with that caused by X-rays, on the simple assumption that each hydrogen peroxide molecule decomposed gives rise to two hydroxyl radicals. Oxygen has very little effect on the actions of the irradiation in glass tubes, but has an appreciable effect in quartz tubes. The following processes have been noted: (1) breakage of the phosphate-sugar link; (2) oxidation of the sugar; (3) fission of the bonds between the sugar and the bases; (4) oxidation of the bases; (5) liberation of the free phosphate. The liberation of phosphate from DNA as well as mono-, di- and tri-ethylphosphates and simple nucleotides has been studied. The results are in accordance with the hypothesis that liberation of phosphate from mono-phosphate esters occurs as the result of a simple reaction; while that of di- and tri-phosphate esters occurs as the result of two and three consecutive reactions, respectively. DNA behaves as a di-ester and the fraction of phosphate-sugar links broken in unit time in the irradiation calculated on this basis is in close agreement with that observed in the case of simpler phosphate esters. The liberation of free phosphate occurs as a consequence of the oxidation of the alkyl or sugar groups.

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