RADIATION DAMAGE TO DNA--EFFECTS OF MODIFIERS AND LET

本研究的目的是测试模型的直接作用机制。 不同LET辐射对DNA的损伤及损伤修复 辐射防护剂。DNA损伤和硫醇的最新模型 我们实验室已经开发出自氧化反应。第一个描述是 从最初的DNA离子自由基到形成的DNA辐射事件 二次自由基，最后是抗磁性产物。第二 描述了硫醇从硫基到磺酰基的自氧化循环 过氧基。我们的调查将测试硫醇对DNA的影响 氧和缺氧体系中的自由基过程，以寻求一种 更好地了解化学增氧作用和硫醇 辐射防护。这些研究是在以下条件下进行的 强调辐射的直接作用，将采用电子自旋 共振光谱(ESR)，使用从头算的理论建模 分子轨道理论(分子轨道计算)和气相色谱--质量 光谱(GC-MS)技术。高LET重离子的效应 对DNA的辐射和硫醇的修复将通过使用 密歇根州立大学的国家超导回旋加速器。 具体地说，在目标一中，对以下方面至关重要的激进机制的调查 DNA的辐射防护和化学增氧作用将 调查过了。包括：1.糖自由基与硫醇的反应 在缺氧和缺氧系统中。2.对硫磺攻击的调查- DNA和DNA组分上的氧(亚硫基)自由基。3. 特异性DNA碱基与硫醇反应的研究 通过实验确定哪些特定的自由基与硫醇发生反应。在……里面 AIM II从头算分子轨道计算也将被用来预测 许多已知的DNA自由基中间体能够参与 硫醇的辐射防护与比较和澄清 实验结果。等键反应的使用将允许 精确的反应能计算。在AIM III调查中 DNA-硫醇体系的高LET辐照将检验这一假设 高LET辐射损伤比低LET辐射损伤更为复杂 正是这种复杂的损伤导致了辐射的减少 在OER和LET中。在AIM IV样品中，用ESR对其进行了研究 将分析AIMS I和III的DNA碱基损伤和碱基释放 GC-MS和高效液相色谱联用技术。产品分析将与Wake联合进行 森林大学。这些分析的结果将用于测试和 进一步阐明ESR实验提出的机制。

The goal of this research is to test models for mechanisms of direct radiation damage to DNA for radiations of varying LET and damage repair by radioprotective agents. Recent models for DNA damage and thiol autoxidation have been developed in our laboratory. The first describes DNA radiation events from the initial DNA ion radicals to the formation of secondary radicals and finally to diamagnetic products. The second describes the autoxidation cycle of thiols from thiyl radical to sulfonyl peroxyl radical. Our investigations will test the effect of thiols on DNA free radical processes in both oxic and anoxic systems in order to seek a better understanding of the chemical oxygen enhancement effect and thiol radioprotection. These studies, which are performed under conditions that emphasize the direct effect of radiation, will employ electron spin resonance spectroscopy (ESR), theoretical modeling using ab initio molecular orbital theory (MO calculations), and gas chromatography--mass spectroscopy (GC-MS) techniques. The effects of high LET heavy ion radiation on DNA and its repair by thiols will be investigated by use of the National Superconducting Cyclotron at Michigan State University. Specifically, in Aim I investigations of radical mechanisms important to DNA radioprotection and the chemical oxygen enhancement effect will be investigated. Included are: 1. The reaction of sugar radicals with thiols in anoxic and oxic systems. 2. The investigation of the attack of sulfur- oxygen (sulfoxyl) radicals on DNA and DNA components. 3. The investigation of the reaction of specific DNA base radicals with thiols to experimentally ascertain which specific radicals react with thiols. In Aim II ab initio MO calculations will also be employed to predict which of the many known DNA radical intermediates are able to participate in radioprotection by thiols for comparison to and elucidation of experimental results. Use of isodesmic reactions will allow for calculation of accurate reactions energies. In Aim III investigations of high LET irradiation on DNA-thiol systems will test the hypothesis that damage by high LET radiation is more complex than that caused by low LET radiation and that it is this complex damage which results in the decrease in OER with LET. In Aim IV samples irradiated and investigated by ESR in Aims I and III will be analyzed for DNA base damage and base release by GC-MS and HPLC. Product analyses will be performed jointly with Wake Forest University. Results of these analyses will serve to test and further elucidate mechanisms proposed by ESR experiments.