There is now strong evidence for the existence of macrocyclic isomers of b _n ⁺ ions, the formation and subsequent opening of which can lead to loss of sequence information from protonated peptides in multiple-stage tandem mass spectrometry experiments. In this study, the fragmentation patterns of protonated YARFLG and permuted isomers of the model peptide were investigated by collision-induced dissociation. Of interest was the potential influence of the arginine residue, and its position in the peptide sequence, on formation of the presumed macrocyclic b₅ ion isomer and potential loss of sequence information. We find that regardless of the sequence position (either internal or at the N- or C-terminus), only direct sequence ions or ions directly related to fragmentation of the arginine side chain are observed.

现在，有强有力的证据表明存在b _n ⁺离子的大环异构体，其形成和随后的开放会导致多阶段串联质谱实验中质子化肽的序列信息丢失。在这项研究中，质子化的YARFLG和模型肽的置换异构体的片段化模式通过碰撞诱导解离进行了研究。感兴趣的是精氨酸残基及其在肽序列中的位置对推测的大环b ₅形成的潜在影响。 离子异构体和序列信息的潜在损失。我们发现，无论序列位置如何（在内部或在N端或C端），仅观察到直接序列离子或与精氨酸侧链断裂直接相关的离子。