GAS-PHASE INTERACTIONS OF LITHIUM IONS AND DIPEPTIDES
GAS-PHASE INTERACTIONS OF LITHIUM IONS AND DIPEPTIDES
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DOI：
10.1021/ja00169a017
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发表时间：
1990-06-20
影响因子：
15
通讯作者：
GROSS, ML
中科院分区：
文献类型：
--
作者：
GRESE, RP;GROSS, ML
FAB和串联质谱已被用来研究气相中锂离子和二肽的相互作用。锂化二肽分解为亚稳离子，产生两个氨基酸离子，分别对应于N-末端（[B1 + Li + OH]+）和C-末端（[Y1 + Li + H]+）。锂离子在第一步中与C-末端的羧酸根阴离子相互作用。碎片离子的相对丰度取决于质子化位点、形成的锂化氨基酸的稳定性和失去的亚胺的稳定性。对于脂肪族二肽，两个氨基酸碎片离子的相对丰度大致相等;然而，如果一个氨基酸含有高质子亲和力的侧链（例如，His、Arg、Lys），氨基酸片段离子（作为[M + Li]+离子）占主导地位。其他侧链如Phe、Met和Ser显示中间行为。在碰撞活化后，C-末端氨基酸的[M + Li]+的产生变得更占主导地位，表明该反应在动力学上有利于更高能量的离子。然而，His、Arg和Lys的[M + Li]+离子仍然占主导地位，使得测序困难。然而，通过使用丰度较低的离子（例如，[A1+ Li-H]+离子和来自侧链损失的那些）。钠离子和钾离子与肽的相互作用与锂离子类似;然而，K+的较低极化能力显著减少了N-末端氨基酸离子的形成。
FAB and tandem mass spectrometry have been used to investigate the gas-phase interactions of lithium ions and dipeptides. Lithiated dipeptides decompose as metastable ions, producing two amino acid ions, those corresponding to the N-terminus ([B1 + Li + OH]+) and the C-terminus ([Y1 + Li + H]+). The lithium ion interacts with the carboxylate anion of the C-terminus in a first step. The relative abundances of the fragment ions depend upon the site of protonation, the stability of the lithiated amino acid formed, and the stability of the imine lost. For aliphatic dipeptides, the relative abundances of the two amino acid fragment ions are approximately equal; however, if one amino acid contains a side chain of high proton affinity (e.g., His, Arg, Lys), that amino acid fragment ion (as a [M + Li]+ ion) dominates. Other side chains such as Phe, Met, and Ser show intermediate behavior. Upon collisional activation, the production of the [M + Li]+ of the C-terminus amino acid becomes more dominant, indicating this reaction is kinetically favored for higher energy ions. [M + Li]+ ions of His, Arg, and Lys, however, still dominate, making sequencing difficult. Structure determination, however, is still possible by using less abundant ions (e.g., [A1 + Li - H]+ ions and those from side chain losses). The interactions of sodium and potassium ions with peptides are similar to that of lithium; however, the lower polarizing power of K+ dramatically reduces the formation of the N-terminus amino acid ion.