Bossée Anne, Afonso Carlos, Fournier Françoise, Tasseau Olivier, Pepe Claude, Bellier Bruno, Tabet Jean-Claude
Centre d'Etudes du Bouchet, BP 3, 91710 Vert le Petit, France.
J Mass Spectrom. 2004 Aug;39(8):903-12. doi: 10.1002/jms.666.
Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed.
使用离子阱质谱仪在负电喷雾电离（ESI）模式下研究了肽与Cu2+的金属化反应。在这些条件下，对形成的[(M - 3H) + CuII]-物种在低能碰撞诱导解离条件下进行了研究。二级质谱（MS2）实验表明，与[M - H]-物种相比，CuII金属化配合物的行为有很大不同。正如之前通过即时“源内”解离实验所观察到的，CuII会导致二氧化碳容易损失，并且在C端残基处发生特定的侧链裂解（通过自由基损失）。二氧化碳的损失会产生一种不稳定的卡拜，从而导致进一步的解离，涉及质子或氢自由基的迁移（通过CuII的还原）。进行了多级三级质谱（MS3）实验以解释这种行为。提出了裂解途径以解释所观察到的产物离子。C端的侧链自由基损失被证明是一个连续过程。最后，有证据表明，当Leu/Ile和Gln/Lys残基位于C端时，特定的侧链裂解可用于区分它们。有人提出在阴离子YGGFK - CuII配合物的情况下存在两性离子形式。
