Production mechanism of DNA bases radical induced by inner-shell excitation

Yokoya, Akinari

To reveal the mechanism of oxidative base damages, such as 8-oxo-G, in DNA molecule by ionizing radiation, DNA base radicals were examined around oxygen and nitrogen K-edge region using an EPR spectrometer installed in a synchrotron soft X-ray beamline (BL23SU) in SPring-8. In situ measurements of EPR spectrum of guanine base revealed that short-lived transient radical species are specifically induced by photoexcitation of a 1s electron to * antibonding orbital at carbonyl oxygen atom. They promptly disappear by "beam-off". On the other hand, a long-lived radical whose EPR spectrum is consistent with previous reports for guanine cation radical was accumulated during the irradiation. The yield of the stable radical decreased by These results indicate that chemically stable DNA base lesions, such as 8-oxo-G, would result from transient species that are inferred to be one electron oxidized radicals after decay of Auger final state.