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Mobile protons versus mobile radicals: Gas-phase unimolecular chemistry of radical cations of cysteine-containing peptides
Journal of the American Society for Mass Spectrometry ( IF 3.2 ) Pub Date : 2010 Aug , DOI: 10.1016/j.jasms.2010.01.027
Adrian K Y Lam 1 , Victor Ryzhov , Richard A J O'Hair
Affiliation  

A combination of electrospray ionization (ESI), multistage, and high-resolution mass spectrometry experiments are used to examine the gas-phase fragmentation reactions of radical cations of cysteine containing di- and tripeptides. Two different chemical methods were used to form initial populations of radical cations in which the radical sites were located at different positions: (1) sulfur-centered cysteinyl radicals via bond homolysis of protonated S-nitrosocysteine containing peptides; and (2) α-carbon backbone-centered radicals via Siu’s sequence of reactions (J. Am. Chem. Soc. 2008, 130, 7862). Comparison of the fragmentation reactions of these regiospecifically generated radicals suggests that hydrogen atom transfer (HAT) between the α C-H of adjacent residues and the cysteinyl radical can occur. In addition, using accurate mass measurements, deuterium labeling, and comparison with an authentic sample, a novel loss of part of the N-terminal cysteine residue was shown to give rise to the protonated, truncated N-formyl peptide (an even-electron xn ion). DFT calculations were performed on the radical cation [GCG].+ to examine: the relative stabilities of isomers with different radical and protonation sites; the barriers associated with radical migration between four possible radical sites, [G.CG]+, [GC.G]+, [GCG.]+, and [GC(S.)G]+; and for dissociation from these sites to yield b2-type ions.



中文翻译:

移动质子与移动自由基:含半胱氨酸肽的自由基阳离子的气相单分子化学

电喷雾电离 (ESI)、多级和高分辨率质谱实验的组合用于检查含有二肽和三肽的半胱氨酸自由基阳离子的气相裂解反应。两种不同的化学方法被用来形成自由基阳离子的初始群体,其中自由基位点位于不同的位置:(1)通过质子化的含 S-亚硝基半胱氨酸的肽的键均裂以硫为中心的半胱氨酰自由基;(2) α-碳骨架中心自由基通过 Siu 的反应序列 ( J. Am. Chem. Soc. 2008, 130, 7862)。这些区域特异性产生的自由基的断裂反应的比较表明,相邻残基的 α CH 与半胱氨酰基自由基之间可能发生氢原子转移 (HAT)。此外,使用准确的质量测量、氘标记以及与真实样品的比较,显示部分 N 端半胱氨酸残基的新损失会产生质子化、截短的 N-甲酰基肽(偶电子 x ñ离子)。对自由基阳离子 [GCG] .+进行 DFT 计算以检查:具有不同自由基和质子化位点的异构体的相对稳定性;与四个可能的自由基位点 [G.CG] +、[GC.G] +之间的自由基迁移相关的障碍, [GCG.] +和 [GC(S.)G] + ; 并从这些位点解离以产生 b 2型离子。

更新日期:2020-03-01
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