Free radical distribution in gamma-irradiated DNA

Previous E.S.R. investigations performed on purine pyrimidine nucleotide complexes, γirradiated at 25°c, showed the occurrence of complete spin transfers from the purine to the pyrimidine nucleotides. The dTMP · dCMP complex has now been investigated under the same conditions and with the following results: among the various dTMP radicals, only the H-addition radicals can be transferred to the dCMP. This result is in agreement with the mechanism suggested previously, according to which, for a transfer to occur the donor molecule must go through an anionic phase during its radical evolution, for, while the á1AH radicals arise from the evolution of T- anions, the other dTMP radicals do not. As a result, they cannot be involved in the transfer and remained localized on dTMP. The validity of this mechanism was again confirmed by the fact that, in the dGMP · dAMP · dTMP · dCMP complex, the two types of transfer take place simultaneously: complete transfers from purine to pyrimidine nucleotides and incomplete transfer from dTMP to dCMP. These results were then applied to the interpretation of the spin migration within the DNA, γirradiated at 25°c. In this molecule, as in the four nucleotide complex, all the radiation damage was localized on the pyrimidine nucleotides. No purine signal was detectable. The modifications of the DNA spectra as a function of several experimental factors were finally studied. They were ascribed to changes in the relative intensities of the pyrimidine patterns in the spectrum. © 1972 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.SCOPUS: ar.j