Abstract
Long-lived radicals (LLRs), assigned as sulfinyl radicals (SLF: R-S-O•), are produced when mammalian cells are γ-irradiated at room temperature. Addition of Vit. C to the cells AFTER irradiation causes the reduction of mutation frequency levels simultaneously with the decrease in the concentration of LLRs. On the carbon ion radiation to mammalian cells followed by addition of Vit. C or Ribose-Cysteine(RibCys), levels of mutation frequency are also decreased although LLRs produced by C-ion beam have not determined yet. In this study, Syrian golden hamster embryonic (SHE) cells were irradiated with C-ion beam at HIMAC as LET: 13.3 keV/μm, 1 kGy, 0.477 kGy/h. Other SHE cells were also γ-irradiated with same dose and dose rate, then the ESR spectra on C-ion and γ-ray radiation were compared. Not only SLF radicals but also thyl (TYL: R-S&bull) radicals were produced by either C-ion and γ-ray radiation. Addition of RibCys to both irradiated cells scavenge SLF radicals, but TYL radicals were scarcely decreased. It indicates that SLF radicals could be mutagenic. A SLF radical is produced by the reaction between a cysteine and a O2— molecule during radiation and is scavenged by Vit. C, RibCys, epigallocatechin-3-O-gallate, N-acetylcysteine, GSH, and so, those chemicals commonly have hydrophilic and hydrogen reducing characters. These results indicate that mutagenic SLF radicals may be generated on the surface of some proteins but TYL radicals may exist in interior of the proteins where is hydrophobic.
