dGMPのOHラジカル付加物に対するシリビンとシリビン誘導体の修復機構

Fast repair activities of silybin and analogues toward dGMP hydroxyl radical adducts

Fu, H.*; 勝村 庸介; Lin, M.; 室屋 裕佐*

Fu, H.*; Katsumura, Yosuke; Lin, M.; Muroya, Yusa*

水溶液中のdGMP(deoxyguanosine monophosphate)のOHラジカル付加物に対するシリビンとシリビン誘導体の修復のメカニズムを解明するためのパルスラジオリシス実験を実施した。0.1mMのシリビン, 2mM dGMPを含む中性水溶液をNOで飽和して用いた実験の結果、dGMPのOHラジカル付加物の吸収スペクトルの減衰と平行してシリビン類のフェノキシラジカルの生成を観測した。これは、dGMPのOHラジカル付加物のシリビンによる修復作用を示しており、その反応速度定数を110Msと決定できた。また、4種のシリビン誘導体の修復反応の速度定数も測定し、その中ではシリビンが最も高修復効率を持つことを示した。これらはフェノキシ系抗酸化剤の一般的な非酵素の迅速修復機構を示している。

The repair activities and mechanisms of both silybin and the analogues towards the oxidizing deoxyguanosine monophosphate (dGMP) hydroxyl radical adduct were investigated with pulse radiolytic technique. On pulse irradiation of nitrous oxide saturated 2.0 mM dGMP aqueous solution containing 0.1 mM silybin at neutral pH (2 mM phosphate buffer), the transient absorption spectrum of the dGMP hydroxyl radical adduct decays with the formation of phenoxyl radical of silybin within tens of microseconds. It indicates that there is a repair reaction between dGMP hydroxyl radical adduct and silybin. The rate constant of the repair reactions was calculated to be 1.010 L mol s for silybin. The repair activity of hesperetin, naringin and naringenin towards hydroxyl radical adducts of dGMP were also observed. Comparison of the rate constants of the four flavanones, silybin shows more effective reparation activities towards dGMP-OH adduct. The results indicate that dGMP radical can be rapidly repaired by silybin and analogues, which also demonstrated that non-enzymatic, fast repair is a universal repair mechanism of phenolic antioxidants.