Department of Chemistry, University of Toronto, Toronto, ON, Canada.
J Am Soc Mass Spectrom. 2009 Dec;20(12):2248-53. doi: 10.1016/j.jasms.2009.08.013. Epub 2009 Aug 27.
The product ion mass spectra obtained by CID of the b(9) ions derived by loss of neutral alanine from the MH+ ion of the peptides Tyr(Ala)9, (Ala)4Tyr(Ala)5, and (Ala)8TyrAla are essentially identical, indicative of full cyclization reaction to a common intermediate before fragmentation. This leads to abundant nondirect sequence ions in the product ion mass spectra of the b9 ions. The product ion mass spectra of the b8 ions from the first two peptides also are essentially identical. The fragmentation of the MH+ ions also leads to low intensity nondirect sequence ions in the product ion mass spectra. N-terminal acetylation blocks the cyclization and eliminates nondirect sequence fragment ions in the product ion mass spectra.
通过对 MH+ 离子失去中性丙氨酸衍生的 b(9) 离子进行 CID 得到的产物离子质谱，得到的 Tyr(Ala)9、(Ala)4Tyr(Ala)5 和 (Ala)8TyrAla 肽的 b(9) 离子基本相同，这表明在碎片化之前，完全环化反应到一个共同的中间体。这导致 b9 离子产物离子质谱中存在丰富的非直接序列离子。前两个肽的 b8 离子的产物离子质谱也基本相同。MH+ 离子的碎片化也会导致产物离子质谱中低强度的非直接序列离子。N-端乙酰化会阻止环化并消除产物离子质谱中的非直接序列片段离子。
