THE EFFECT OF FIXED CHARGE MODIFICATION ON ECD

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。 对两种修饰的β淀粉样多肽(20-29和25-35)进行了电子捕获研究，以探讨H+自由基在多肽离子电子捕获中的作用和自由基级联(FRC)机制。使用2，4，6-三甲基吡啶(TMP)作为固定电荷标记，它具有捕获电子时同时捕获原始形成的自由基并抑制H+产生的潜力。用电子捕获检测器分析未标记、单标记和双标记的多肽。研究发现，固定电荷基团的数目和位置都影响这些多肽在ECD中的主链和侧链的裂解。随着固定电荷标签的加入，主链裂解的频率和程度降低，侧链裂解的频率和程度增加。标签间隔较远的双标记多肽产生的多个侧链裂解较少，但主干裂解略多于邻近标签的双标记肽。尽管双标记多肽离子的所有带电位置都是非质子化的，但在它们的ECD谱中仍然观察到了几个低丰度的c和z+离子。因此，虽然H+转移对N-C(α)键的断裂可能是重要的，但也存在其他途径。最后，这种特殊自由基陷阱的存在似乎只是抑制了FRC途径，但并没有消除FRC途径，该途径很可能是通过空间中的H+提取进行的，并产生了大量的侧链和主干裂解。这项研究最近发表在《美国质谱学学会杂志》上(Li等人，2008，19,1514-1526)。

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. ECD studies of two modified Amyloid beta peptides (20-29 and 25-35) were performed to investigate the role of H+ radicals in the ECD of peptide ions and the free radical cascade (FRC) mechanism. 2,4,6-trimethylpyridinium (TMP) was used as the fixed charge tag, which has the potential of simultaneously trapping the originally formed radical upon electron capture and inhibiting the H+ generation. Unlabeled, singly-labeled, and doubly-labeled peptides were each analyzed by ECD. It was found that both the number and locations of the fixed charge groups influenced the backbone and side-chain cleavages of these peptides in ECD. The frequency and extent of backbone cleavages decreased and those of side-chain cleavages increased with the addition of fixed charge tags. A doubly-labeled peptide with tags spaced far apart produced fewer multiple side-chain cleavages, but slightly more backbone cleavages than the one with neighboring tags. Despite the non-protonated nature of all charged sites in doubly-labeled peptide ions, several low abundance c and z+ ions were still observed in their ECD spectra. Thus, while H+ transfer may be important for the N-C(alpha) bond cleavage, there also exist other pathways. Finally, it appeared that the presence of this particular radical trap merely inhibited but did not eliminate the FRC pathway which most likely proceeded via H+ abstraction through space and produced numerous sidechain and backbone cleavages. This study has been recently published (Li et al., 2008) in the Journal of the American Society for Mass Spectrometry, 2008, 19, 1514-1526.