Mechanism of the induction of DNA strand breaks by low energy radiation

电离辐射转移器的能量最大，对许多低能量的二级电子，并产生最大的辐射生物学效应。真空和远紫外线光子提供了一种独特的工具来控制能量吸收过程、刺激和电离。单色低能电子和光子，它们是放射生物学效应的强制机制的必要条件，但是，无论如何，它们在辐射生物学中使用得非常明显，因为缺乏方便的来源。我们的项目是通过两个独特的辐射来源，利用两个独特的辐射来源进行DNA链断裂诱导机制的国际合作：单色低能电子（英国格雷实验室）和单色真空-紫外光光子（日本光子工厂）。关于血浆DNA中链断裂指数的主要结果如下; （1）电子与15个Ev诱导的ssb和dsb线性地指示ssb和dsb的指数的阈值能量低于15 Ev ;对dsb的价值的实验确定是这个项目的主要结果之一。（2）dsb / ssb的比率约为0.01，其中与D160的D1Co γ-rays相似。（3）低能光子下降到4.3 Ev （经测试的最低能量）诱导的ssb和dsb，量子场非常低。这一结果表明，在这种意义上，阈值能量低于4.3 Ev，但通常定义的能量约为10 Ev。（4）我们通过真空-紫外线光子在缓冲区解决方案中被辐射的等离子体DNA，该方法是在灰色实验室开发的;单色7-Ev光子已被用于ssb和dsb。（5）这些阈值能量对于模拟DNA断裂模型的计算是至关重要的。

Most energy of ionizing radiation transfers to many low energy secondary electrons, and then they produce most radiobiological effects. Vacuum-and far-UV photons provide an unique tool to control the energy absorbing processes, excitation and ionization. Monochromatic low energy electrons and photons, thus, are essential to elucidate mechanism of radiobiological effects, but, however, they are scarcely used in radiation biology because of lack of convenient sources. Our project is an international cooperation to elucidate mechanism of the induction of DNA strand breaks using two unique radiation sources : monochromatic low energy electrons (Gray Laboratory, UK) and monochromatic vacuum-UV photons (Photon Factory, Japan). Major results on the strand break induction in plasmid DNA are as follows ; (1) electrons as low as 15 Ev induced ssb and dsb linearly with the fluence, indicating that the threshold energy for the induction of ssb and dsb is below 15 Ev ; experimental determination of the value for dsb is one of the major result of this project. (2) The ratio of dsb / ssb was about 0.01, which was similar to that for ィイD160ィエD1Co γ-rays. (3) Low energy photons down to 4.3 Ev (the lowest energy tested) induced ssb and dsb with very low quantum yield. This result indicated that the threshold energy was lower than 4.3 Ev in this sense, but that defined usual was about 10 Ev. (4) We irradiated plasmid DNA in buffer solution by vacuum-UV photons using the method that was developed in the Gray Laboratory ; monochromatic 7-Ev photons induced ssb and dsb. (5) These threshold energies are crucially important to simulation calculation of models for DNA strand break.