General and Physical Chemistry Department, Mass Spectrometry Laboratory, Liege University, Liege, Belgium.
J Am Soc Mass Spectrom. 2010 Nov;21(11):1906-17. doi: 10.1016/j.jasms.2010.07.009. Epub 2010 Aug 1.
In-source decay (ISD) is a rapid fragmentation occurring in the matrix-assisted laser desorption/ionization (MALDI) source before the ion extraction. Despite the increasing interest for peptides de novo sequencing by ISD, the influence of the matrix and of the peptide itself is not yet fully understood. Here we compare matrices with high ISD efficiencies to gain deeper insight in the ISD fragmentation process(es). The major ISD fragments are the c- and z-ions, but other types of fragments are also observed, and their origin is studied here. Two main pathways lead to fragmentation in the source: a radical-induced pathway that leads to c-, z-, w-, and d-ions, and a thermally activated pathway that leads to y-, b-, and a-ions. A detailed analysis of the ISD spectra of selected peptides revealed that (1) the extents of the two in-source pathways are differently favored depending on the matrix used, that (2) the presence of a positive/negative charge on the radical-induced fragments is necessary for their observation in positive/negative mode, respectively, and that (3), for a same peptide, the patterns of the different types of fragments differ according to the matrix used.
内源衰退（ISD）是在基质辅助激光解吸/电离（MALDI）源中的离子提取之前发生的快速碎裂。尽管人们对通过 ISD 对肽进行从头测序越来越感兴趣，但基质和肽本身的影响尚未完全理解。在这里，我们比较了具有高 ISD 效率的基质，以更深入地了解 ISD 碎裂过程。主要的 ISD 碎片是 c-和 z-离子，但也观察到其他类型的碎片，并且在这里研究了它们的起源。在源中导致碎裂的两种主要途径：一种是自由基诱导的途径，导致 c-、z-、w-和 d-离子，另一种是热激活途径，导致 y-、b-和 a-离子。对选定肽的 ISD 光谱的详细分析表明：（1）两种内源途径的程度根据所使用的基质而不同，（2）在正/负离子模式下分别观察到自由基诱导碎片上存在正/负电荷是必要的，以及（3）对于相同的肽，根据所使用的基质，不同类型的碎片的模式不同。
