Abstract
We have proposed Long-Lived Radicals (LLRs) in proteins might be related to delayed radiation effects. Both heavy-ion or γ-ray radiation to mammalian cells with the same doses gives almost the same frequencies of the point mutation, but it is larger in complex mutation for the heavy-ion ray. In order to measure the ESR spectra of mammalian cells which have under an active metabolism, we have prepared instruments for cell culture. In this study, the cultured Syrian golden Hamster Embryo (SHE) cells were irradiated with C-ion beam at HIMAC (LET: 55.9 keV/μm) or γ-ray at Nagoya Univ. with the same dose and dose rate of 1 kGy and 0.82 kGy/h, respectively. Non-irradiated cultured cells showed a broadened ESR signal due to at least four radical species. Two species are assigned as a thiyl and a flavin anion radicals, and other two species might be some organic radicals. In addition to these species, a signal due to a hydrogen-added phenylalanine radical was observed in the ESR spectra of the γ-ray irradiated cells. Only a signal due to thiyl radical were detected in the cells irradiated by C-ion beam, and other radicals in non-irradiated or γ-irradiated cells were disappeared. The difference in existing radical species in the cells might be related to the stability of environments where the disappeared radicals exist against to γ-ray and C-ion irradiation. Further investigation is required for clarifying the issue of the difference, and we will investigate the delayed radiation effects through the measurements and identification of the LLRs.
