Abstract

VUV action spectroscopy has recently gained interest for the study of peptides and proteins. However, numerous aspects of the fundamental processes involved in the photodissociation are yet to be understood. It can, for example, be expected that sulfur-containing amino-acid residues have a significant impact on the dissociation processes following photoionization because of their potential involvement in the transport of electron holes in proteins. In order to investigate the influence of the sulfur-containing methionine residue on the VUV photodissociation of a small peptide a VUV action spectroscopy study of gas-phase protonated methionine-enkephalin and leucine-enkephalin in the photon energy range of 6–35 eV was performed. The results show that upon non-ionizing photoexcitation, the fragmentation patterns of the two peptides are nearly identical, whereas significant differences were observed upon photoionization. The differences between the fragment yields and the identified specific dissociation channels for methionine-enkephalin could be explained by the high electron hole affinity of sulfur, which efficiently directs the radical to the methionine side chain. Additionally, for both peptides the presence of the intact photoionized precursor ions was confirmed by their isotopic patterns and the stability of these species could be evaluated.

Graphic abstract

中文翻译：

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蛋氨酸残基对VUV作用光谱探测光电离蛋氨酸-脑啡肽解离机理的影响

摘要

VUV作用光谱法最近引起了对肽和蛋白质研究的兴趣。然而，光解离所涉及的基本过程的许多方面尚待理解。可以预期，例如，含硫氨基酸残基对光电离后的解离过程具有重大影响，因为它们潜在地参与了蛋白质中电子空穴的运输。为了研究含硫蛋氨酸残基对小肽的VUV光解离的影响，对气相质子化蛋氨酸-脑啡肽和亮氨酸-脑啡肽在6–35 eV的光子能量范围内进行了VUV作用谱研究。结果表明，在非电离光激发下，两种肽的片段化模式几乎相同，而在电离时观察到显着差异。硫代的高电子空穴亲和力可有效地将自由基引导至蛋氨酸侧链，从而解释了蛋氨酸-脑啡肽的片段收率与已确定的特定解离通道之间的差异。另外，对于这两种肽，通过其同位素模式证实了完整的光电离的前体离子的存在，并且可以评估这些物质的稳定性。可以有效地将自由基引导至蛋氨酸侧链。另外，对于这两种肽，通过其同位素模式证实了完整的光电离的前体离子的存在，并且可以评估这些物质的稳定性。可以有效地将自由基引导至蛋氨酸侧链。另外，对于这两种肽，通过其同位素模式证实了完整的光电离的前体离子的存在，并且可以评估这些物质的稳定性。

图形摘要