Sequence dependent long range hole transport in DNA
Sequence dependent long range hole transport in DNA
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DOI：
10.1021/ja983092p
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发表时间：
1998-12-16
影响因子：
15
通讯作者：
Giese, B
中科院分区：
文献类型：
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作者：
Meggers, E;Michel-Beyerle, ME;Giese, B
鸟嘌呤自由基阳离子(G(+.))在双链DNP中选择性地生成，并研究了不同序列中的电荷转移。该方法是基于G(+.)通过DNA及其与H2O的捕捉反应。我们分析了这个G(+)的空穴转移。通过一个、两个、三个和四个AT碱基对连接到GGG单元，并发现每个介入的AT碱基对的速率降低了约1个数量级。这种强烈的距离依赖性导致贝塔值为0.7+/-0.1埃(-1)。在本实验的时间尺度内，当G(+)被来自GGG单位的四个AT碱基对分开。然而，如果四个插入的AT碱基对中的第二个或第三个被GC碱基对交换，则G(+.)对GGG单位增加了2个数量级。此外，在含有AT和GC碱基对的混合链中，可以观察到超过15个碱基对的远程电荷转移。因为G(+.)可以氧化G碱基，但不能氧化A碱基，长程电荷传输可以用G碱基之间正电荷的跃迁来解释。因此，混合链中的总电荷传输是G碱基之间的多步骤跳跃过程，其中单个步骤对总速率有贡献。距离依赖关系不再由超交换机制的贝塔值来描述，
A guanine radical cation (G(+.)) was site-selectively generated in double stranded DNP, and the charge transfer in different oligonucleotide sequences was investigated. The method is based on the competition between a charge transfer from G(+.) through the DNA and its trapping reaction with H2O. We analyzed the hole transfer from this G(+.) to a GGG unit through one, two, three, and four AT base pairs and found that the rate decreases by about 1 order of magnitude with each intervening AT base pair. This strong distance dependence led to a beta-value of 0.7 +/- 0.1 Angstrom(-1). Within the time scale of this assay the charge transfer nearly vanished when the G(+.) was separated by four AT base pairs from the GGG unit. However, if the second or the third of the four intervening AT base pairs was exchanged by a GC base pair, the rate of the hole transfer from the G(+.) to the GGG unit increased by 2 orders of magnitude. In addition, a long-range charge transfer over 15 base pairs could be observed in a mixed strand that contained AT as well as GC base pairs. Because G(+.) can oxidize G but not A bases, the long-range charge transport can be explained by a hopping of the positive charge between the intervening G bases. Thus, the overall charge transport in a mixed strand is a multistep hopping process between G bases where the individual steps contribute to the overall rate. The distance dependence is no longer described by the beta value of the superexchange mechanism,