MECHANISTIC STUDIES OF ELECTRON CAPTURE DISSOCIATION BY DEUTERIUM LABELING

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们最近关于环肽ECD的数据表明，广泛的自由基介导的二次碎裂正在发生。回过头来看，仅仅观察到电子俘获产生的[M+2H]1+自由基离子就意味着存在长寿命(1秒)的自由基阳离子。由于自由基被认为是高度不稳定的，而且以前环肽的电子捕获数据显示了广泛的重排，所以设计了一个简单的实验来验证这一假说。购买了一对含有4个甘氨酸残基的合成肽。在一种多肽中，甘氨酸被标记在α碳上，从而生成D2-甘氨酸。另一种多肽使用正常甘氨酸。如果一个寿命较长的自由基经历了广泛的重排，预计随着自由基在多肽上向上和向下迁移，该自由基将不分青红皂白地从α碳位上提取氢和氚。很可能会有一种动力学的同位素效应，这将减缓重氢的迁移，但在1秒的时间尺度上不太可能观察到这一点。 正常和D2-甘氨酸修饰的多肽的电子捕获图显示出重离子扰乱，这意味着自由基确实通过从α碳(至少是甘氨酸的)中抽出氢(或重氢)而重排和迁移。经过多番努力和多次修改，这篇论文终于在2006年春季发表。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our recent data on ECD of cyclic peptides implied extensive free-radical mediated secondary fragmentation was occurring. In retrospect, the mere observation of the [M+2H]1+ radical ion resulting from the electron capture implies the existence of long lived ( 1 second) radical cations. Since radicals are known to be highly unstable, and since the previous data on ECD of cyclic peptides implied extensive rearrangment, a simple experiment was devised to test this hypothesis. A pair of synthetic peptides were purchased which contained 4 glycine residues. In one peptide, the glycines were deuterium labeled on the alpha carbon thus creating D2-glycine. The other peptide used normal glycine. If a long lived radical undergoes extensive rearrangment, it was expected that the radical will abstract hydrogens and deuteriums indiscriminately from the alpha carbon sites as the radical migrates up and down the peptide. There is likely to be a kinetic isotope effect that will slow down the migration of the deuterium, but this is unlikely to be observable on a 1 second timescale. ECD of the normal versus D2-Glycine modified peptide showed deuterium scrambling which implies that the radical does rearrange and migrate via hydrogen (or deuterium) abstraction from the alpha carbons (of glycine at least). After much effort and many revisions, this paper was finally published in spring 2006.