AN INVESTIGATION OF FRAGMENTATION MECHANISMS OF DOUBLY PROTONATED TRYPTIC PEPTIDES
AN INVESTIGATION OF FRAGMENTATION MECHANISMS OF DOUBLY PROTONATED TRYPTIC PEPTIDES
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DOI：
10.1002/rcm.1290061105
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发表时间：
1992-11-01
影响因子：
2
通讯作者：
BOYD, RK
中科院分区：
文献类型：
--
作者：
TANG, XJ;BOYD, RK
作为胰蛋白酶特异性水解蛋白质的反应产物而形成的肽，其特征是 C 末端有碱性残基（Arg 或 Lys），这有助于在电喷雾或离子喷雾条件下形成丰富的 [M + 2H]2+ 离子。这些双电荷离子在碰撞激活时很容易解离成彼此质量互补的 y" 和 b 碎片离子。这些碎片是通过直接电荷分离解离形成的建议必须与 y" 强度通常明显大于其 b 对应物的观察结果相矛盾。然而，研究表明，这可以通过 b 离子更容易进一步解离成更小的碎片（例如铵离子）来解释。此外，没有发现证据支持替代机制，包括解离电子捕获，对于该机制，两个碎片离子系列的相等强度不是强制性的。通过 N 末端的单乙酰化抑制，N 末端的初始质子化是形成这些 [M + 2H]2+ 离子所必需的。这些发现以及有关 [y"']2+ 片段形成的其他发现，与已发表的从单质子化肽分别通过电荷位点诱导裂解和氮原子之间的分子内质子转移形成 b 和 y" 片段的机制的扩展是一致的。
Peptides formed as reaction products, of specific hydrolysis of proteins by trypsin, are characterized by a basic residue (Arg or Lys) at the C-terminus, which facilitates formation of abundant [M + 2H]2+ ions under electrospray or ionspray conditions. These doubly charged ions readily dissociate upon collisional activation to y" and b fragment ions which are mass complements of one another. The suggestion that these fragments are formed by direct charge-separation dissociations must contend with the observation that the y" intensities are generally appreciably larger than those of their b counterparts. However, it is shown that this can be accounted for by a greater susceptibility of the b ions to undergo further dissociation to smaller fragments such as immonium ions. In addition no evidence could be found to support alternative mechanisms, including dissociative electron capture, for which equal intensities of the two fragment ion series are not obligatory. Initial protonation at the N-terminus was shown to be required for formation of these [M + 2H]2+ ions via its suppression by mono-acetylation at the N-terminus. These findings, and others concerning formation of [y"']2+ fragments, are consistent with extensions of published mechanisms for formation of b and of y" fragments from singly protonated peptides, via charge-site-induced cleavages and intramolecular proton transfers between nitrogen atoms, respectively.