Mass Spectrometry Laboratory, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, Japan.
J Am Soc Mass Spectrom. 2019 Sep;30(9):1592-1600. doi: 10.1007/s13361-019-02245-z. Epub 2019 Jul 8.
The source of hydrogen in the formation of c- and y-ions produced by intramolecular hydrogen transfer in negative-ion CID experiments with peptides has been examined using Cα-, Cβ-, and backbone amide (N)-deuterated peptides AAA(d3)AA, AAG(d2)AA, AAAG(d2)A, and AAAAA-d7, as well as five other peptides. The c- and y-ions produced by deuterium transfer from the deuterated residues were detected and identified by the exact m/z values obtained with a high-resolution orbitrap mass spectrometer. The rate of deuterium transfer obtained indicates that over 50% of the hydrogen was originated from the backbone amide nitrogen, with the residual hydrogen coming from the backbone Cα. It is clear that the hydrogen does not originate from the side chain Cβ. It is hypothesized that the intramolecular hydrogen transfer to form negative c- and y-ions takes place via 3-, 4-, 6-, 7-, 8-, and 9-membered ring transition states.
采用 Cα-、Cβ-和骨架酰胺（N）-氘代肽 AAA(d3)AA、AAG(d2)AA、AAA(d2)A 和 AAAAA-d7 以及其他五种肽，研究了在肽的负离子 CID 实验中通过分子内氢转移生成 c-和 y-离子的氢源。通过高分辨率轨道阱质谱仪获得的精确 m/z 值检测和鉴定了从氘代残基转移而来的 c-和 y-离子。氘转移的速率表明，超过 50%的氢来源于骨架酰胺氮，剩余的氢来自骨架 Cα。显然，氢不是来自侧链 Cβ。据推测，通过 3-、4-、6-、7-、8-和 9 元环过渡态形成负 c-和 y-离子的分子内氢转移发生。
