DNA damage spectra in ultrasoft X-ray region; Effect of ionization of carbon, nitrogen and oxygen atoms on the damage induction

軟X線領域でのDNAダメージスペクトル; 炭素・窒素及び酸素の内殻電離の効果

藤井 健太郎; 横谷 明徳; 鹿園 直哉

Fujii, Kentaro; Yokoya, Akinari; Shikazono, Naoya

軟X線照射によって乾燥DNA中に生じる分子主鎖切断及び酸化的塩基損傷の収率をアガロース電気泳動法により検出した。塩基損傷の検出は、照射試料を塩基除去修復酵素で処理することによって塩基損傷を鎖切断に変換することで定量化した。それぞれの収率は、軟X線のエネルギーに依存し、特に酸素K殻吸収によって鎖切断及び塩基損傷の収率の有意な増加が見られた。講演ではこれらのDNA損傷の生成機構について議論する。

To investigate the K-shell photo-ionization effect (photoelectric effect and subsequent secondary electron impact) on DNA damage, dry plasmid DNA (pUC18) films (sample thickness) were irradiated with monochromatic ultrasoft X-rays (270, 380, 435, 560, and 760eV) from a soft X-ray undulator beamline in SPring-8 (BL23SU) in a vacuum. Irradiated sample was analyzed by agarose gel electrophoresis and the yields of single- (SSB) and double-strand breaks (DSB) were determined by measuring the band intensities of the separated closed circular, open circular and linear form of the plasmid DNA. The yields of purine and pyrimidine base lesions were also determined by the post-irradiation-treatment of the DNA sample with enzymatic probes (Fpg and Endo III) which excise a base lesion and visualized it as a strand break.