Induction of strand breaks in single-stranded polyribonucleotides and DNA by photoionization: One electron oxidized nucleobase radicals as precursors
Induction of strand breaks in single-stranded polyribonucleotides and DNA by photoionization: One electron oxidized nucleobase radicals as precursors
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DOI：
10.1021/ja961722m
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发表时间：
1996-10-23
影响因子：
15
通讯作者：
ONeill, P
中科院分区：
文献类型：
--
作者：
Melvin, T;Botchway, SW;ONeill, P
作为电离辐射直接效应的模型，研究了193 nm激光脉冲照射后单链DNA样品（小牛胸腺、溶壁微球菌、产气荚膜梭菌）、polyC、polyU和polyA在pH 7.5-8的含氧水溶液的光散射强度（LSI）的时间分辨变化。LSI的变化（单链断裂形成的指数）与瞬态光吸收的变化（一个指数的核酸基自由基化学）脉冲193-nm照射后的比较表明，链断裂发生在类似的DNA，聚C，聚U，但不是聚A的核酸基自由基物种的衰变率。除了聚腺苷酸，193-nm的光导致LSI的减少超过类似于0.2秒，表明链断裂发生的核碱基自由基介导的过程，从而核碱基自由基位点转移到糖部分。对于polyU和polyC，LSI的显著变化也发生在更快的时间尺度上（3 ms内）。在DNA中，单电子氧化位点主要位于鸟嘌呤，并且所产生的单电子氧化鸟嘌呤自由基导致链断裂，与主要的非链断裂途径竞争。
As a model for the direct effect of ionizing radiation, time-resolved changes of light-scattering intensity (LSI) of aqueous, oxic solutions of single-stranded DNA samples (calf thymus, Micrococcus lysodeikticus, Clostridium perfingens), polyC, polyU, and polyA at pH 7.5-8 have been studied following pulse irradiation with 193-nm laser light. A comparison of LSI changes (an index of single-strand break formation) with transient optical absorption changes (an index of nucleic acid base radical chemistry) following pulsed 193-nm irradiation shows that strand breakage occurs at rates similar to those for the decay of the nucleic acid base radical species for DNA, polyC, and polyU but not for polyA. With the exception of polyA, 193-nm light leads to a reduction in the LSI over similar to 0.2 s, indicating that strand breakage occurs by a nucleobase radical-mediated process, whereby the nucleobase radical site is transferred to the sugar moiety. With polyU and polyC, significant changes in LSI also occur on a much faster time scale, (within 3 ms). In DNA, the one electron oxidized sites become localized predominantly at guanine and the resulting one electron oxidised guanine radicals lead to strand breakage in competition with major, non-strand-breakage pathways.