THE EFFECT OF FIXED CHARGE MODIFICATION ON ECD

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目及 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 对两种修饰的淀粉样蛋白β肽（20-29和25-35）进行ECD研究，以研究H+自由基在肽离子的ECD中的作用和自由基级联（FRC）机制。使用2，4，6-三甲基吡啶鎓（TMP）作为固定电荷标签，其具有在电子捕获时同时捕获最初形成的自由基和抑制H+产生的潜力。未标记的、单标记的和双标记的肽各自通过ECD分析。结果发现，固定电荷基团的数量和位置的影响，这些肽在ECD的主链和侧链的切割。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。一个双标记的肽与标签间隔很远，产生较少的多个侧链裂解，但稍微更多的骨干裂解比一个相邻的标签。尽管双标记肽离子中所有带电位点的非质子化性质，但仍在其ECD光谱中观察到几种低丰度c和z+离子。因此，虽然H+转移对于N-C（α）键断裂可能是重要的，但也存在其他途径。最后，似乎这种特殊的自由基陷阱的存在仅抑制但不消除FRC途径，其最有可能通过空间H+提取进行，并产生许多侧链和主链裂解。这项研究最近发表（Li et al.，2008）在Journal of the American Society for Mass Spectrometry，2008，19，1514-1526中。

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.