Induction of DNA-Protein Crosslinks in Chinese Hamster V79-4 Cells Exposed to High- and Low-Linear Energy Transfer Radiation

Abstract

The induction of DNA-protein crosslinks (DPCs) in Chinese hamster V79-4 cells after irradiation under hypoxic and aerobic conditions at 277 K with 60Co gamma rays, 238Pu alpha particles and aluminum K (Al(K)) ultrasoft X rays has been determined using a nitrocellulose filter binding assay. The dose dependences for the induction of DPCs, which involves covalent linkage, are linear over the absorbed dose range used (0-400 Gy with alpha-particle and gamma radiation, 0-600 Gy with Al(K) X rays). The yield of DPCs induced under hypoxic conditions is 55, 51 and 25 DPCs per gray per cell for 60Co gamma rays, alpha particles and Al(K) X rays, respectively. The yield of DPCs is significantly reduced in the presence of oxygen by 20, 50 and 79% for 60Co gamma rays, alpha particles and Al(K) X rays, respectively. Since the mean size of the DNA attached to the protein is uniform for 60Co gamma rays and alpha particles, variations in the DNA size do not influence the yields of DPCs. Although a DPC may be considered as a complex lesion combining two macromolecules, the dependence of the yield of DPCs on LET does not reflect the ionizing density of the radiations used. Further, this dependence on LET and the effect of oxygen do not reflect the corresponding dependences determined for a variety of biological responses. From these findings and knowledge of the radiation tracks, it is proposed that DPCs induced particularly under aerobic conditions with 60Co gamma rays are formed mainly in the sparsely ionizing segments of the radiation track.