Fragmentation reactions of protonated peptides containing glutamine or glutamic acid
Fragmentation reactions of protonated peptides containing glutamine or glutamic acid
复制标题
DOI：
10.1002/jms.427
复制
发表时间：
2003-02-01
影响因子：
2.3
通讯作者：
Harrison, AG
中科院分区：
文献类型：
--
作者：
Harrison, AG
用电喷雾电离和快原子轰击电离制备了一系列含谷氨酸或谷氨酰胺的质子化二肽和三肽，并通过亚稳离子研究、能量分辨质谱和三级质谱实验阐明了它们的裂解途径。通过用氘替换不稳定的氢获得了更多的机理信息。在亚稳离子碎片化中通过NH3损失和H2O损失质子化H-Gln-Gly-OH碎片;在碰撞诱导解离（CID）条件下，[MH-NH3]（+）离子的H-Gly- OH + CO损失形成基峰C4 H6 NO+（m/z 84）。具有α键H-Glu-Xxx-OH的质子化二肽的特征在于消除H2O和消除H-Xxx-OH加CO以形成m/z 102的谷氨酸亚铵离子。相比之下，具有γ-键H-Glu（Xxx-OH）-OH的质子化二肽不显示H2O的消除或m/z 102的形成，而是显示NH3的消除，特别是在亚稳离子碎裂中，以及H-Xxx-OH的消除以形成m/z 130。α-和γ-二肽均显示形成[H-Xxx-OH]H+，随着H-Xxx-OH的质子亲和力（PA）增加，该反应通道的重要性增加。对于质子化的α-三肽H-Glu-Gly-Phe- OH，观察到H2O的特征损失和m/z 102的形成，而质子化的γ-三肽H-Glu（Gly-Gly- OH）- OH显示出NH3的损失和m/z 130的形成，如对于具有γ-键的二肽所观察到的。在CID条件下，两种三肽均显示出丰富的y（2）-离子形成，推测是因为可以形成稳定的酸酐中性结构。在亚稳离子条件下，结构为H-Xxx-Glu-OH的质子化二肽显示出大量的H2O消除，而结构为H-Xxx-Gln-OH的质子化二肽显示出大量的NH3消除。在CID条件下，这些反应通道的重要性大大降低，主要的断裂模式是酰胺键断裂以形成α 1离子或γ（1）-离子。特别地，当Xxx = Gly时，在CID条件下，从含谷氨酰胺的二肽中初始损失NH3之后是第二NH3的消除，而从谷氨酸二肽中初始损失H2O之后是NH3的消除。同位素标记表明，主要是不稳定的氢在这两个步骤中丢失。虽然[H-Gly-Glu-Gly-OH]H+和[H-Gly-Gln-Gly-OH]H+主要断裂形成B（2）和a（2）离子，但后者也显示出NH 3+甘氨酸残基的消除和质子化甘氨酰胺的形成。同位素标记显示在质子化甘氨酰胺的形成中不稳定氢和碳键合氢的广泛混合。版权所有（C）2003约翰威利父子有限公司。
A variety of protonated dipeptides and tripeptides containing glutamic acid or glutamine were prepared by electrospray ionization or by fast atom bombardment ionization and their fragmentation pathways elucidated using metastable ion studies, energy-resolved mass spectrometry and triple-stage mass spectrometry MS3) experiments. Additional mechanistic information was obtained by exchanging the labile hydrogens for deuterium. Protonated H-Gln-Gly-OH fragments by loss of NH3 and loss of H2O in metastable ion fragmentation; under collision-induced dissociation (CID) conditions loss of H - Gly - OH + CO from the [MH - NH3](+) ion forms the base peak C4H6NO+ (m/z 84). Protonated dipeptides with an alpha-linkage, H-Glu-Xxx-OH, are characterized by elimination of H2O and by elimination of H-Xxx-OH plus CO to form the glutamic acid immonium ion of m/z 102. By contrast, protonated dipeptides with a gamma-linkage, H-Glu(Xxx-OH)-OH, do not show elimination of H2O or formation of m/z 102 but rather show elimination of NH3, particularly in metastable ion fragmentation, and elimination of H-Xxx-OH to form m/z 130. Both the alpha- and gamma-dipeptides show formation of [H-Xxx-OH]H+, with this reaction channel increasing in importance as the proton affinity (PA) of H-Xxx-OH increases. The characteristic loss of H2O and formation of m/z 102 are observed for the protonated alpha-tripeptide H - Glu - Gly - Phe - OH whereas the protonated gamma-tripeptide H - Glu(Gly - Gly - OH) - OH shows loss of NH3 and formation of m/z 130 as observed for dipeptides with the gamma-linkage. Both tripeptides show abundant formation of the y(2)" ion under CID conditions, presumably because a stable anhydride neutral structure can be formed. Under metastable ion conditions protonated dipeptides of structure H-Xxx-Glu-OH show abundant elimination of H2O whereas those of structure H-Xxx-Gln-OH show abundant elimination of NH3. The importance of these reaction channels is much reduced under CID conditions, the major fragmentation mode being cleavage of the amide bond to form either the a, ion or the y(1)" ion. Particularly when Xxx = Gly, under CID conditions the initial loss of NH3 from the glutamine containing dipeptide is followed by elimination of a second NH3 while the initial loss of H2O from the glutamic acid dipeptide is followed by elimination of NH3. Isotopic labelling shows that predominantly labile hydrogens are lost in both steps. Although both [H-Gly-Glu-Gly-OH]H+ and [H-Gly-Gln-Gly-OH]H+ fragment mainly to form b(2) and a(2) ions, the latter also shows elimination of NH3 plus a glycine residue and formation of protonated glycinamide. Isotopic labelling shows extensive mixing of labile and carbon-bonded hydrogens in the formation of protonated glycinamide. Copyright (C) 2003 John Wiley Sons, Ltd.