PHOTOINDUCED AND RADIO-INDUCED RADICAL OXIDATION OF THE PURINE AND PYRIMIDINE-BASES OF NUCLEIC-ACIDS

Our current knowledge of the hydroxyl radical-mediated oxidations of the base moiety of the four main DNA 2'-deoxyribonucleosides, in aerated aqueous solutions, is reviewed. Included are kinetic and mechanistic aspects of transient radicals and structural features of the diamagnetic decomposition products. Another major topic addressed in this survey involves the chemical reactions of the purine and pyrimidine radical cations of the above DNA model compounds. These radicals are the main reactive intermediates of the direct effect of ionizing radiation and photosensitized reactions involving type I processes. Emphasis is placed on the similarities between the formation of oxidizing radicals via hydroxyl radical addition to the base moieties and chemical reactions of the radical cations (hydration and/or deprotonation). A survey of the main base lesions which have been characterized within isolated and cellular DNAs under conditions of oxidative stress, including exposure to ionizing radiation and various radiomimetic agents, is also presented.