PHOTOCHEMICAL REACTIONS OF THYMINE WITH CARBOXYLIC ACIDS. A MODEL FOR NUCLEIC ACID-PROTEIN PHOTOCROSSLINKING |
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| Authors: | Francine Toulme Claude Hélène |
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| Institution: | Centre de Biophysique Moléculaire, CNRS, 1A, Avenue de la Recherche Scientifique, 45045 Orleans Cedex, France |
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| Abstract: | When nucleic acid bases are UV-irradiated in the presence of carboxylic acids or carboxylate anions new photoproducts are formed as compared to the bases irradiated in the absence of carboxylic acids. The behavior of thymine and thymidine has been examined in detail. At least four photoproducts are formed in the presence of propionic acid and three in the presence of butyric acid. None of them appears to be a cyclobutyl dimer. From the concentration dependence of the rate of photoproduct formation it is concluded that the reactive excited species is the first excited singlet state of thymine. When 14C-labelled thymine is irradiated in the presence of polyglutamic acid an important part of the radioactive material is covalently linked to the polymer. Photochemical reaction of thymine with glutamic (or aspartic) acid could thus induce crosslinks between proteins and nucleic acids. It is also shown that these photoproducts are stable under usual conditions of acidic hydrolysis of UV-irradiated DNA. |
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