Köcher Thomas, Engström Ake, Zubarev Roman A
Laboratory for Biological and Medical Mass Spectrometry, Uppsala University, Husargatan 3, Box 583, SE-75123 Uppsala, Sweden.
Anal Chem. 2005 Jan 1;77(1):172-7. doi: 10.1021/ac0489115.
In-source decay (ISD) in matrix-assisted laser desorption/ionization (MALDI) shares some similarities with the novel fragmentation technique electron capture dissociation (ECD). In both reactions, the otherwise strong N-C(alpha) bond is cleaved, forming fragment ions of the c and z types, while labile posttranslational modifications are preserved. Therefore, it is tempting to assume that ISD and ECD have some mechanistic aspects in common. Because electrons are present in the MALDI plume, we investigated the previously suggested possibility that ISD is a variation of ECD. However, experiments with peptides with only one site for efficient protonation revealed that ISD is not caused by electron capture. Instead, ICD seems to be induced by hydrogen atoms generated by a photochemical reaction of the matrix. We provide evidence for this reaction by hydrogen/deuterium exchange experiments with peptides containing a minimal number of exchangeable hydrogen atoms. The hydrogen atom model in ECD is indirectly supported by the proposed fragmentation mechanism for ISD, because our data suggest that hydrogen radicals can induce fragmentation by cleavage of the N-C(alpha) bond, independent from their origin.
基质辅助激光解吸/电离（MALDI）中的源内衰变（ISD）与新型碎裂技术电子捕获解离（ECD）有一些相似之处。在这两种反应中，原本很强的N-Cα键都会断裂，形成c型和z型碎片离子，同时不稳定的翻译后修饰得以保留。因此，很容易认为ISD和ECD在某些机制方面有共同之处。由于MALDI羽流中存在电子，我们研究了之前提出的ISD是ECD变体的可能性。然而，对只有一个有效质子化位点的肽进行的实验表明，ISD不是由电子捕获引起的。相反，ISD似乎是由基质的光化学反应产生的氢原子诱导的。我们通过对含有最少可交换氢原子的肽进行氢/氘交换实验，为该反应提供了证据。ECD中的氢原子模型得到了ISD提出的碎裂机制的间接支持，因为我们的数据表明氢自由基可以通过N-Cα键的断裂诱导碎裂，而与它们的来源无关。
