Author： de Jong J. Loman H. Blok Joh.
Publisher： Informa Healthcare
ISSN： 1362-3095
Source： International Journal of Radiation Biology, Vol.22, Iss.1, 1972-07, pp. : 11-21
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Abstract
To investigate the possibility of the involvement of organic radicals, e.g. those derived from amino acids, in the inactivation of DNA in living cells by ionizing radiation, we studied, as a model system, dilute solutions of the biologically-active DNA of the bacteriophage ΦX174 in the presence of relatively high concentrations of phenylalanine. The solutions were saturated with N2, O2 or N2O and irradiated with 60Co γ-rays. Under these conditions a negligible fraction of the primary water radicals reacts with DNA. Nevertheless inactivation of DNA occurs, due to reactions of amino-acid radicals. These reactions probably do not produce DNA chain breaks, but another type of nucleotide damage, which has not yet been identified. In anoxic solutions the phenylalanine radicals can be reduced or oxidized by small amounts of cysteamine and paranitroacetophenone, respectively, which prevents their attack on DNA, resulting in an enormous protection. Moreover, it was found that the ratio of breaks and other damages in DNA in the presence of cysteamine or paranitroacetophenone is considerably lower than in the case where simple attack by water radicals occurs. This suggests that both compounds react with DNA radicals, thereby modifying the radiation damage.
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