RADIATION-INDUCED LONG LIVED RADICALS CAUSING MUTATION AND TRANSFORMATION

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Many researches studying in area of radiation biology have been believed that active short life-time radicals such as OH and H radicals, play an important role to express genoto do effects of radiation h cells, such as mutation and cancer induction. However, we found a new type of radicals with long life-time (T_<1/2>20hr) in gamma ray hmdiated golden hamster embryo (GHE) cells at room temperature by using ESR spectroscopy. It may be more important in mutation induction than the active short live radials. When Vitamin C (MA) is added to the gamma-or X-irradiated cells at 20 min or 6 hr after the irradiation, respectively, LLR are scavenged by them simuhaneousty with the drastic suppression of genotoxicity such as mutation and transformation. Since reactive oxygen species (ROS) disappear within microsecond after the irradiation, AsA do not scavenge the ROS but LLR. Therefore, we have proposed that LLR must be responsible radicals for inducing mutation, and probably important for the genotoxicity in the irradiated mammalian cells. Addition of AsA to the cells before or after irradiation does not have any effects on reducing cell death and chromosomal aberration. By the studies using ESEEM spectroscopy, we found that LLR probably locate in interior of biopolymers where few water molecules exist. By further analysis of the ESR spectra of LLR and comparison of the yields of radicals in proteins and DNA, we reached to the conclusion that LLR are produced in protein and assigned as sulfinyl radicals as oxidized cysteine groups. LLR are not produced in DNA or in lipids. Our result show that the LLR produced in protein is responsible for the gene mutation in irradiated cells. Although this contradicts now common view in the radiation biology, many unresolved phenomena in the radiation biology can be explained well.