A CONTRIBUTION TO THE PROBLEM OF FORMATION OF UREA IN THE RADIOLYSIS OF THYMINE

Journal/Book: Reprinted from Collection of Czechoslovak Chemical Communications Vol. 33 (1968). 1968;

Abstract: Institute of Biophysics Czechoslovak Academy of Sciences Brno A large number of various radiolytic products are formed during the irradiation of aqueous solutions of thymine by ionizing radiation. In some of these product the cyclic structure is preserved e.g. in thymine-hydroperoxide thymine-glycols dihydrothymine monohydroxy derivatives of dihydrothymine 5-hydroxymethyluracil and in derivatives of barbituric acid. Urea which is formed by the rupture of the pyridimine ring by radiation was also detected among the products of radiolysis of thymine1 2. The conversion of some molecules of thymine into urea might be one of the causes for the change in biological properties of the irradiated desoxyribonucleic acid (DNA)1. According to our opinion this process might play a certain role in the radiation damage of living objects only if urea were one of the primary products of the radiolysis of thymine or of other pyrimidine bases. The chemical structure of urea differs so much from that of thymine that obviously it cannot be formed in a single reaction between a pyrimidine base and one of the products of radiolysis of water. We must therefore suppose either a simultaneous effect of several radicals an one molecule or a successive degradation of radiolytic products of thymine during the irradiation. The radiationchemical yield of urea as given e.g. by Nofre2 is rather low (G = 006-011). It is impossible to decide with certainty which of the above mentioned processes participates substantially in the formation of urea because at the present time we cannot determine precisely the probability of simultaneous collision of one thymine molecuIe with two or more products of water radiolysis. . . .

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