Abstract
Several chemical and conformational factors have been shown to interfere with the radiolytic pathways in ..gamma..-irradiated DNA, producing different radical populations on the macromolecule. These factors include anoxic or oxic conditions, relative hydration degree, denaturation and/or degradation, and base composition. This led to extreme variations in the ESR spectra. Nevertheless, computer-assisted analysis of these spectra revealed the following common composition: a doublet from thymine anions (T/sup -/), a singlet from guanine cations (G/sup +/), an octet from 5-thymly radicals (TH), and an asymmetrical doublet from thymine-located peroxyl radicals (TOO). This formal interpretation of the experimental spectra permitted us to elucidate the following basic features for DNA radiolysis in frozen aqueous solution; Neutral DNA solutions frozen at 77 K are phase-seperated systems. Radiation damage to DNA does not result from the indirect effects of radiation; Primary radicals on DNA are ions of both signs, randomly produced on the constituent bases; Charge migration occurs via the stacked bases. Thymine is the eventual sink of the long-range electron migration. Guanine is the eventual sink of the short-range positive hole migration. Migration phenomena may be partially or totally hindered by various interfering factors; With increase in temperature, ionic radicals enter conversion reactions: G/sup +/more » decays without reacting with the surrounding water molecules, whereas T/sup -/ does react to form the 5-thymyl radical; In the presence of oxygen, peroxyl radicals TOO are formed rather than 5-thyml radicals; No sugar-located free radicals have been detected in the course of the present investigation.« less
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