FRAGMENTATION PROPERTIES OF OXIDIZED PEPTIDES BY ERGODIC & NON-ERGODIC METHODS

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。 羟基自由基足迹实验的氧化位点的指定是通过串联质谱仪进行的，其中氧化肽在质谱仪中被激活，所产生的裂解模式与计算的理论裂解模式进行比较，并分析差异以确定氧化发生在哪里。然而，侧链的氧化改变了遍历裂解方法中的裂解化学，通常导致裂解产物的数量较少，这使得氧化位点的绝对分配变得困难。我们正试图利用更高的能量进行遍历碎裂，再加上以较低的质量与电荷比进行扫描，试图找到特征的侧链离子和侧链损失，这些离子和侧链损失是特定氨基酸残基氧化的诊断，以便简化氧化位点的分配。另一个经常出现的困难是氧化异构体的问题；氧化异构体是一种在两个或多个位置发生氧化的多肽。通过简单地量化碎片离子的丰度是不可能量化每个位置上的氧化速率的，因为氧化在遍历过程中影响碎片本身的模式。最近的工作表明，非遍历碎裂方法，如电子捕获解离(ECD)对侧链氧化不敏感，这表明碎片离子丰度可能有助于定量氧化肽的异构体混合物。我们将氧化具有多个氧化位点的模型多肽，并研究ECD产生的碎片离子的丰度。这些丰度将与氧化肽酸解产生的氧化和未氧化氨基酸的丰度进行比较，以确定用ECD片段离子丰度进行定量是否可行。

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. Assignment of oxidation sites for hydroxyl radical footprinting experiments is done by means of tandem mass spectrometry, where the oxidized peptide is activated in the mass spectrometer and the resulting fragmentation pattern is compared to a computed theoretical fragmentation pattern, and the differences analyzed to determine where the oxidation occurred. However, the oxidation of side chains alters the fragmentation chemistry in ergodic fragmentation methods, often resulting in a smaller number of fragmentation products which makes absolute assignment of sites of oxidation difficult. We are attempting to utilize higher energies for ergodic fragmentation, coupled with scanning at lower mass to charge ratios, to try to find characteristic side chain ions and side chain losses that are diagnostic of oxidation at a particular amino acid residue, in order to simplify the assignment of oxidation sites. Another difficulty that often arises is the matter of oxidation isomers; a peptide on which oxidation occurs at two or more sites. Quantitation of the rates of oxidation on each site is not possible by simply quantitating the abundances of fragment ions, as oxidation affects the pattern of fragmentation itself in ergodic processes. Recent work has suggested that non-ergodic fragmentation methods such as electron capture dissociation (ECD) are insensitive to side chain oxidation, suggesting that fragment ion abundances may be useful for quantitating isomeric mixtures of oxidized peptides. We will be oxidizing model peptides with multiple oxidation sites and studying the abundances of fragment ions generated by ECD. These abundances will be compared with the abundances of oxidized and unoxidized amino acids generated by acid hydrolysis of the oxidized peptide in order to determine if quantitation by ECD fragment ion abundance is feasible.