Chemical Effects of Ionizing Radiations on Nucleic Acids and Nucleoproteins

Abstract

RECENT work¹ on the effects of ionizing radiations on nucleic acids (deoxyribonucleic and ribonucleic acids) in aqueous systems has shown quite clearly that the reactive species produced from the water attack mainly the constituent purine and pyrimidine bases and, to a lesser extent, the sugar moieties of these polynucleotide molecules. The extents of destruction of the individual bases on irradiation of deoxyribonucleic solutions (0.005 per cent) in the presence of oxygen (1 atm.) were measured and found to be as follows (G = molecules/100 eV.) : G(− Δthymine) = 0.33 ; G(− Δadenine) = 0.25 ; G(− Δcytosine) = 0.23 ; G(− Δguanine) = 0.18. Breakage of the strands in the deoxyribonucleic acid helix is apparently mainly due to an attack of the radicals produced by irradiation on the sugar moieties, which leads to a splitting of the phosphate ester linkages along the chains. The extent of attack which leads to breakage of internucleotide bonds, leading to the production of phosphomonoester groups, has been determined directly with monophosphoesterase ; the number of end-groups formed on irradiation with 200 kV. X-rays gives a yield of G ≃ 0.5. Rupture of hydrogen bonds within the helix is a consequence of chemical changes in the polynucleotide chains ; several hydrogen bonds can be broken following a single chemical event.