Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada,
J Am Soc Mass Spectrom. 2013 Oct;24(10):1565-72. doi: 10.1007/s13361-013-0707-9. Epub 2013 Aug 6.
The fragmentation reactions of the MH(+) ions of Leu-enkephalin amide and a variety of heptapeptide amides have been studied in detail as a function of collision energy using a QqToF beam type mass spectrometer. The initial fragmentation of the protonated amides involves primarily formation of bn ions, including significant loss of NH3 from the MH(+) ions. Further fragmentation of these bn ions occurs following macrocyclization/ring opening leading in many cases to bn ions with permuted sequences and, thus, to formation of non-direct sequence ions. The importance of these non-direct sequence ions increases markedly with increasing collision energy, making peptide sequence determination difficult, if not impossible, at higher collision energies.
采用 QqToF 型质谱仪，详细研究了亮氨酸脑啡肽酰胺和各种七肽酰胺的 MH(+)离子的碎裂反应随碰撞能的变化情况。质子化酰胺的初始碎裂主要涉及 bn 离子的形成，包括 MH(+)离子中显著的 NH3 损失。这些 bn 离子进一步碎裂，发生大环化/开环，导致许多情况下 bn 离子的序列发生置换，从而形成非直接序列离子。随着碰撞能的增加，这些非直接序列离子的重要性显著增加，使得在较高碰撞能下，肽序列的确定变得困难，如果不是不可能的话。
