Where are the sugar radicals in irradiated DNA?
Where are the sugar radicals in irradiated DNA?
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DOI：
10.2307/3579478
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发表时间：
1997-06-01
影响因子：
3.4
通讯作者：
Close, DM
中科院分区：
文献类型：
--
作者：
Close, DM
在X射线辐照的核苷和核苷酸中，用EPR和Endor光谱观察到了大量的糖自由基。然而，在辐照的DNA中没有观察到糖自由基。存在一种可能性，即糖自由基可能以相对较小的丰度存在，因此到目前为止没有被检测到。另一种可能性是，五个以碳为中心的H-抽象糖基中的每一个都可能以广泛的构象存在。将具有不同超精细偶合和各向异性g因子的不同基团加在一起可能会得到很宽的EPR谱线，这将很难被检测到。利用B-DNA十二聚体的晶体结构，计算了5个H-抽提糖基在所有位置的构象。然后使用从不同自由基构象计算的典型的α-质子和β-质子耦合来模拟每个自由基的X波段EPR谱。结果表明，C-2‘，C-3’H-抽象基的EPR谱线有相当大的展宽。通过在DNA谱中添加15%的H-抽提基来模拟复合EPR谱。结果表明，C-1‘自由基的外线是可见的，应该很容易识别。几乎看不到C-2‘和C-3’自由基的宽谱。C-4‘和C-5’自由基的模拟光谱基本上是二重态，被DNA信号遮挡。(C)1997年，由辐射研究学会提供。
Numerous sugar radicals have been observed by EPR and ENDOR spectroscopy in X-irradiated nucleosides and nucleotides. However, no sugar radicals have been observed in irradiated DNA. One possibility exists that sugar radicals may be present in relatively small abundance and therefore have so far escaped detection. Another possibility is that each of the five carbon-centered H-abstraction sugar radicals may exist in a wide range of conformations. Adding together various groups of radicals with different hyperfine couplings and anisotropic g factors may result in very broad EPR lines which would be difficult to detect. Using the crystal structure of a B-DNA dodecamer, the conformations of the five H-abstraction sugar radicals have been computed at all sites. The X-band EPR spectra for each radical were then simulated using typical alpha-proton and beta-proton couplings computed from the various radical conformations. The results suggest considerable broadenings of the EPR lines for the C-2', C-3' H-abstraction radicals. Composite EPR spectra were simulated by adding 15% of an H-abstraction radical to the DNA spectrum. The results indicate that the outer lines of the C-1' radical are visible and should be easy to identify. The broad spectra of the C-2' and C-3' radicals are barely visible. The simulated spectra of the C-4' and C-5' radicals are basically doublets and are obscured by the DNA signal. (C) 1997 by Radiation Research Society.