Chemical Investigations of the Molecular Origin of Biological Radiation Damage

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Abstract
The radiation damage observed when UV and ionizing radiations react on biological objects is caused in many cases by changes in the nucleic acids. Exposure of these compounds to UV radiation in vitro and in vivo leads, inter alia, to dimerization of the pyrimidine bases with formation of cyclobutane derivatives, and to addition of water to the 5,6‐double bond of the pyrimidine bases to form derivatives of the 6‐hydroxyhydropyrimidine system. The structure of the irradiation products has been established. The dimerization prevents the reduplication of the DNA, and the addition of water appears to be the cause of UV mutations. Ionizing radiation in aqueous solution results e.g. in addition of H and/or HO radicals to the 5,6‐double bond of the pyrimidine bases and cleavage of the imidazole ring of the purine bases. The mutations caused by ionizing radiation are probably also due, in part, to the formation of 6‐hydroxydihydropyrimidine derivatives.