The nonapeptide oxytocin (OT) is used as a model sulfur-containing peptide to study the damage induced by vacuum UV (VUV) radiations. In particular, the effect of the presence (or absence in reduced OT) of oxytocin’s internal disulfide bridge is evaluated in terms of photo-fragmentation yield and nature of the photo-fragments. Intact, as well as reduced, OT is studied as dianions and radical anions. Radical anions are prepared and photo-fragmented in two-color experiments (UV + VUV) in a linear ion trap. VUV photo-fragmentation patterns are analyzed and compared, and radical-induced mechanisms are proposed. The effect of VUV is principally to ionize but secondary fragmentation is also observed. This secondary fragmentation seems to be considerably enabled by the initial position of the radical on the molecule. In particular, the possibility to form a radical on free cysteines seems to increase the susceptibility to VUV fragmentation. Interestingly, disulfide bridges, which are fundamental for protein structure, could also be responsible for an increased resistance to ionizing radiations.

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九肽催产素（OT）用作模型含硫肽，用于研究真空UV（VUV）辐射引起的损伤。特别地，根据光致碎裂的产率和光致碎裂的性质来评估催产素内部二硫键的存在（或不存在降低的OT）的影响。完整的和还原的OT被研究为双阴离子和自由基阴离子。在线性离子阱中的双色实验（UV + VUV）中，制备了自由基阴离子并进行了光碎。分析和比较了VUV的光碎裂模式，并提出了自由基诱导的机理。VUV的作用主要是电离，但也观察到二次断裂。自由基在分子上的初始位置似乎极大地促进了这种二次断裂。尤其是，在游离半胱氨酸上形成自由基的可能性似乎增加了对VUV片段化的敏感性。有趣的是，对蛋白质结构至关重要的二硫键也可能导致对电离辐射的抵抗力增强。

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