Computational Proteomics Group, German Cancer Research Center, Heidelberg, Germany.
J Phys Chem A. 2010 Apr 22;114(15):5076-82. doi: 10.1021/jp9113046.
Multiple-stage tandem mass spectrometry and collision-induced dissociation were used to investigate loss of H(2)O or CH(3)OH from protonated versions of GGGX (where X = G, A, and V), GGGGG, and the methyl esters of these peptides. In addition, wavelength-selective infrared multiple photon dissociation was used to characterize the M + H - H(2)O product derived from protonated GGGG and the major MS(3) fragment, M + H - H(2)O - 29 of this peak. Consistent with the earlier work [ Ballard , K. D. ; Gaskell , S. J. J. Am. Soc. Mass Spectrom. 1993 , 4 , 477 - 481 ; Reid , G. E. ; Simpson , R. J. ; O'Hair , R. A. J. Int. J. Mass Spectrom. 1999 , 190/191 , 209 -230 ], CID experiments show that M + H - H(2)O is the dominant peak generated from both protonated GGGG and protonated GGGG-OMe. This strongly suggests that the loss of the H(2)O molecule occurs from a position other than the C-terminal free acid and that the product does not correspond to formation of the b(4) ion. Subsequent CID of M + H - H(2)O supports this proposal by resulting in a major product that is 29 mass units less than the precursor ion. This is consistent with loss of HN horizontal lineCH(2) rather than loss of carbon monoxide (28 mass units), which is characteristic of oxazolone-type b(n) ions. Comparison between experimental and theoretical infrared spectra for a group of possible structures confirms that the M + H - H(2)O peak is not a substituted oxazolone but instead suggests formation of an ion that features a five-membered ring along the peptide backbone, close to the amino terminus. Additionally, transition structure calculations and comparison of theoretical and experimental spectra of the M + H - H(2)O - 29 peak also support this proposal.
采用多级串联质谱和碰撞诱导解离技术，研究了质子化 GGGX（其中 X = G、A 和 V）、GGGGG 以及这些肽的甲酯中 H₂O 或 CH₃OH 的缺失。此外，还采用波长选择性红外多光子解离技术，对质子化 GGGG 衍生的 [M+H-H₂O]⁺产物以及该峰的主要 MS³碎片 [M+H-H₂O-29]⁺进行了表征。与早期的工作 [ Ballard, K. D. ; Gaskell, S. J. J. Am. Soc. Mass Spectrom. 1993, 4, 477 - 481 ; Reid, G. E. ; Simpson, R. J. ; O'Hair, R. A. J. Int. J. Mass Spectrom. 1999, 190/191, 209 -230 ] 一致，CID 实验表明，[M+H-H₂O]⁺是由质子化 GGGG 和质子化 GGGG-OMe 生成的主要峰。这强烈表明，H₂O 分子的缺失发生在除了 C 末端游离酸以外的位置，并且产物与 b(4)离子的形成不对应。随后对 [M+H-H₂O]⁺的 CID 支持了这一假设，结果得到的主要产物比前体离子少 29 质量单位。这与失去 HN 水平键 CH₂而不是失去一氧化碳（28 质量单位）一致，这是氧杂唑啉型 b(n)离子的特征。一组可能结构的实验和理论红外光谱的比较证实，[M+H-H₂O]⁺峰不是取代的氧杂唑啉，而是形成了一种特征为沿肽骨架的五元环的离子，靠近氨基末端。此外，过渡态结构计算和 [M+H-H₂O-29]⁺峰的理论和实验光谱的比较也支持了这一假设。
