RADIATION DAMAGE TO DNA--EFFECTS OF MODIFIERS AND LET

本研究的目的是测试模型的机制，直接 不同LET辐射对DNA的辐射损伤和损伤修复 辐射防护剂。 DNA损伤和巯基的最新模型 自氧化反应已在我们的实验室发展起来。 第一个描述了 DNA辐射事件从最初的DNA离子自由基的形成 次级自由基，最后转化为抗磁性产物。 第二 描述了硫醇从硫酰基自由基到磺酰基的自氧化循环 过氧自由基 我们的研究将测试硫醇对DNA的影响 在好氧和缺氧系统中的自由基过程，以寻求 更好地理解化学氧增强效应和硫醇 辐射防护 这些研究是在以下条件下进行的， 强调辐射的直接效应，将采用电子自旋 共振光谱（ESR），从头算理论建模 分子轨道理论（MO计算）和气相色谱-质谱 光谱（GC-MS）技术。 高LET重离子效应 辐射对DNA及其修复硫醇将研究使用 密歇根州立大学的国家超导回旋加速器。 具体而言，在目标I中，对以下重要的自由基机制进行了研究： DNA辐射防护和化学氧增强效应将是 研究了 包括：1.糖基与硫醇的反应 在缺氧和好氧系统中。 2.关于硫磺袭击的调查- 氧（亚砜）自由基对DNA和DNA成分。 3.的 研究特定DNA碱基自由基与硫醇的反应， 通过实验确定哪些特定的自由基与硫醇反应。 在 目的II从头计算MO计算也将用于预测哪一个 许多已知的DNA自由基中间体能够参与 硫醇的辐射防护作用，用于比较和说明 试验结果 使用等键反应将允许 精确计算反应能量。 在Aim III中， 对DNA-硫醇系统的高LET辐照将检验以下假设： 高LET辐射造成的损伤比低LET辐射造成的损伤更为复杂 辐射，正是这种复杂的损伤导致了 在OER与LET。 In Aim IV样品辐照和ESR研究 将通过以下方法分析目的I和III的DNA碱基损伤和碱基释放： GC-MS和HPLC。 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.