Multifunctional Repair Enzymes Excise Thymine and Adenine Residues Damaged by Ionizing Radiation from DNA
Aerobic metabolism is associated with the chance occurrence of reactive forms of oxygen, which may damage DNA (1–3). Analogous lesions are formed by ionizing radiation (4–6). It has been suggested that many dietary mutagens and carcinogens act through the production of oxygen radicals (7), and the deleterious free radical reactions involving oxygen have also been implicated in the genesis of spontaneous cancer in man (8) as well as in the aging process (9). It has been reported recently (10) that rats, which have a higher basal metabolic rate and shorter life span than humans, excrete in their urine 15 times more thymine glycol (an oxidation product of thymine) per unit body mass compared to humans, though what proportion of this that is derived from tRNA is not clear. Radiation-induced base damage in DNA is known to make an important contribution to the lethal and mutagenic effects observed in vivo (11, 12). Consequently, repair enzymes which act on DNA damaged by ionizing radiation and oxidizing agents are important in the preservation of the genome and prevention of mutagenesis and carcinogenesis.
KeywordsPotassium Permanganate Ataxia Telangiectasia Crude Cell Extract Adenine Residue Basal Cell Nevus Syndrome
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