Ultraviolet-Laser-Induced Electron Transfer from Peptides to an Oxidizing Matrix: Study of the First Step of MALDI In-Source Decay Mass Spectrometry
Ultraviolet-Laser-Induced Electron Transfer from Peptides to an Oxidizing Matrix: Study of the First Step of MALDI In-Source Decay Mass Spectrometry
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紫外激光诱导电子从肽转移到氧化基质：MALDI 源内衰变质谱第一步的研究
DOI：
10.1021/jasms.0c00186
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发表时间：
2020
影响因子：
3.2
通讯作者：
Asakawa Daiki
中科院分区：
文献类型：
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作者：
Asakawa Daiki
尽管多肽骨架中的N-H键比C-H键更强，但在使用氧化基质时，从酰胺氮中夺氢被认为是基质辅助激光解吸/电离源内衰变(MALDI-ISD)中肽骨架Cα-C键断裂的第一步。MALDI-ISD导致大多数氨基酸残基的C-α-C键断裂，而Pro残基的N-末端优先发生肽键断裂，这不能用先前提出的多肽脱氢机制来解释。为了解释MALDI-ISD过程的整个过程，提出了氧化基质从多肽中提取电子作为MALDI-ISD过程的第一步。电子夺取发生在肽骨架上的氮或氧上，并导致大多数氨基酸残基上的C-α-C和N-H键断裂，但Pro残基的N-末端侧除外。Pro残基上的电子抽离导致多肽和Cα-C键的断裂，这与MALDI-ISD实验结果一致。多肽向氧化基质的电子转移与基质离子的形成同时发生，这被认为是MALDI的初始离子形成过程。生成的多肽自由基阳离子产生质子化和中性分子/自由基，在MALDI羽流中经历随后的离子-分子反应，最终产生在MALDI-ISD光谱中观察到的离子。结果，MALDI-ISD形成的碎片离子既有正离子，也有负离子。
Although the N–H bond in peptide backbones is stronger than the C–H bond, hydrogen abstraction from the amide nitrogen is considered to be the initial step in the Cα–C bond cleavage of peptide backbones by matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) when using an oxidizing matrix. MALDI-ISD induces Cα–C bond cleavage in most amino acid residues, whereas the N-terminal sides of proline (Pro) residues preferentially undergo peptide bond cleavage, which cannot be explained by the previously proposed mechanism involving hydrogen abstraction from peptides. To explain the whole MALDI-ISD process, electron abstraction from peptides by the oxidizing matrix is proposed as the initial step in the MALDI-ISD process. The electron abstraction occurs from either nitrogen or oxygen in the peptide backbone and induces the cleavage of both Cα–C and N–H bonds in most amino acid residues, except for those on the N-terminal sides of Pro residues. Electron abstraction from the Pro residues induces the cleavage of both peptide and Cα–C bonds, which is consistent with MALDI-ISD experimental results. The electron transfer from the peptide to the oxidizing matrix occurs simultaneously with the formation of matrix ions, which is considered to be the initial ion formation process in MALDI. The resultant peptide radical cation produces protonated and neutral molecules/radicals, which undergo subsequent ion–molecule reactions in the MALDI plume, finally yielding the ions that are observed in MALDI-ISD spectrum. As a result, the fragment ions formed by MALDI-ISD are observed as both positive and negative ions.