Prise K M, Davies S, Michael B D
Cancer Research Campaign Gray Laboratory, Mount Vernon Hospital, Northwood, Middlesex, United Kingdom.
Radiat Res. 1993 Apr;134(1):102-6.
Isolated plasmid pBR322 DNA was irradiated in the gas explosion apparatus in the presence of 10 mmol dm-3 GSH. By varying the time of the oxygen shot relative to the 5-ns pulse of electrons, the chemical repair kinetics of the oxygen-dependent free-radical precursors of DNA single- and double-strand breaks (SSBs and DSBs) can be determined. The first-order repair rate of the SSB precursors was 1370 s-1 in comparison to 2900 s-1 for DSB precursors. Under these conditions the oxygen enhancement ratio for SSBs was 3.0 in comparison to 7.5 for DSBs. This twofold difference in chemical repair rate may be interpreted on the basis of the free-radical precursor of a DSB consisting of two radicals, one on either strand of the DNA. With the chemical repair of one or other of these radicals by hydrogen atom donation from GSH, a DSB is not produced. This process will occur at twice the rate of the chemical repair of an SSB precursor consisting of a single radical. These data are consistent with the concept that DSBs are formed at the sites of clustered energy depositions with the production of a paired radical.
在含有10 mmol dm-3谷胱甘肽（GSH）的情况下，将分离出的质粒pBR322 DNA置于气体爆炸装置中进行辐照。通过改变相对于5纳秒电子脉冲的充氧时间，可以确定DNA单链和双链断裂（SSB和DSB）的氧依赖性自由基前体的化学修复动力学。SSB前体的一级修复率为1370 s-1，而DSB前体的一级修复率为2900 s-1。在这些条件下，SSB的氧增强比为3.0，而DSB的氧增强比为7.5。化学修复率的这两倍差异可以基于DSB的自由基前体由两个自由基组成来解释，这两个自由基分别位于DNA的两条链上。通过GSH提供氢原子对其中一个或另一个自由基进行化学修复时，不会产生DSB。这个过程的发生速率将是由单个自由基组成的SSB前体化学修复速率的两倍。这些数据与以下概念一致，即DSB在聚集能量沉积位点形成，并产生一对自由基。
