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

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。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。所列机构为 中心，不一定是研究者的机构。 用于羟基自由基足迹实验的氧化位点的分配通过串联质谱法进行，其中氧化肽在质谱仪中活化，并且将所得的断裂模式与计算的理论断裂模式进行比较，并且分析差异以确定氧化发生的位置。 然而，侧链的氧化改变了各态历经断裂方法中的断裂化学，通常导致较少数量的断裂产物，这使得难以绝对分配氧化位点。 我们正试图利用更高的能量遍历碎片，再加上扫描在较低的质荷比，试图找到特征侧链离子和侧链损失的诊断氧化在一个特定的氨基酸残基，以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;氧化发生在两个或多个位点的肽。 通过简单地定量碎片离子的丰度来定量每个位点上的氧化速率是不可能的，因为氧化影响遍历过程中碎片化本身的模式。 最近的工作表明，非遍历的碎片化方法，如电子捕获解离（ECD）是不敏感的侧链氧化，这表明碎片离子丰度可能是有用的定量异构体混合物的氧化肽。 我们将氧化具有多个氧化位点的模型肽，并研究ECD产生的碎片离子的丰度。 将这些丰度与氧化肽酸水解产生的氧化和未氧化氨基酸的丰度进行比较，以确定通过ECD碎片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.