Formation of Hydroperoxides from Nucleic Acids by Irradiation with X-Rays in Aqueous Systems

Abstract

IN the course of our studies of the chemical effects of X-rays on nucleic acids in aqueous solutions¹, we have had occasion to measure the amounts of peroxide produced. Two methods were employed: (a) the reaction with titanium sulphate reagent² and spectrophotometric measurement of the resulting complex at 405 mµ ; (b) the oxidation of potassium iodide³ and determination of the liberated iodine (I₃ ⁻) by the absorption at 353 mµ. It was found that, in solutions of thymus deoxyribonucleic acid and also of yeast ribonucleic acid irradiated in the presence of oxygen, the yields of total peroxide, as determined by the iodide method, were always greater than those of hydrogen peroxide, estimated by titanium sulphate. This observation can be explained by the presence of organic hydroperoxides in the irradiated nucleate solutions, since it is known that hydro-peroxides will oxidize iodide ions, but do not give, in general, the coloured complex with the titanium sulphate reagent.