Division of Physiological Chemistry I, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
J Am Soc Mass Spectrom. 2013 Nov;24(11):1671-5. doi: 10.1007/s13361-013-0628-7. Epub 2013 Apr 30.
Analysis of large (>10,000 entries) databases consisting of high-resolution tandem mass spectra of peptide dications revealed with high statistical significance (P < 1[Symbol: see text]10(-3)) that peptides with non-identical first two N-terminal amino acids undergo cleavages of the second peptide bond at higher rates than repetitive sequences composed of the same amino acids (i.e., in general AB- and BA- bonds cleave more often than AA- and BB- bonds). This effect seems to depend upon the collisional energy, being stronger at lower energies. The phenomenon is likely to indicate the presence of the diketopiperazine structure for at least some b2 (+) ions. When consisting of two identical amino acids, these species should form through intermediates that have a symmetric geometry and, thus, must be subject to the Jahn-Teller effect that reduces the stability of such systems.
对包含肽二阳离子的高分辨率串联质谱的大型（>10000 个条目）数据库进行分析，结果表明，在统计学上具有高度显著性（P<1[Symbol: see text]10(-3)），与由相同氨基酸组成的重复序列相比，前两个 N 末端氨基酸不同的肽经历第二肽键的裂解速度更快（即，一般 AB-和 BA-键比 AA-和 BB-键更容易断裂）。这种效应似乎取决于碰撞能，在较低的能量下更强。该现象很可能表明至少存在一些 b2 (+) 离子的二酮哌嗪结构。当由两个相同的氨基酸组成时，这些物质应该通过具有对称几何形状的中间体形成，因此必须受到 Jahn-Teller 效应的影响，从而降低了此类系统的稳定性。
