Ackermann B L, Barbuch R J, Coutant J E, Krstenansky J L, Owen T J
Marion Merrell Dow Research Institute, Cincinnati, OH 45215-6300.
Rapid Commun Mass Spectrom. 1992 Apr;6(4):257-64. doi: 10.1002/rcm.1290060407.
A fragmentation process observed for peptides that contain lysine, or other amino acids which possess a free amino group on their sidechain, is reported. The ions generated by this process are found 16 Da below the acylium-type B ions that result from fragmentation at the C-terminal side of lysine or other amine-containing residues in fast-atom bombardment (FAB) mass spectra. These ions, which are referred to as (B-16) ions, permit differentiation between the isobaric amino acids lysine and glutamine in peptide mass spectra. High resolution measurements indicate that (B-16) ions differ in composition from the corresponding B ions by the removal of one oxygen atom. Formation is believed to occur through a cyclization process initiated by nucleophilic attack by the free amino group of the lysine sidechain at the carbon of the acylium ion (B ion). A similar process initiated directly from the protonated peptide may also occur. Analogous cyclization processes are restricted for glutamine because this residue is comparatively less nucleophilic than lysine (i.e., amide vs amine). Although (B-16) ions have been detected under high energy collisionally induced dissociation, they are formed less readily than by FAB mass spectrometry. A mechanism consistent with this observation as well as other experimental evidence is presented to account for the formation of (B-16) ions.
据报道，对于含有赖氨酸或其他在其侧链上带有游离氨基的氨基酸的肽，会观察到一种碎片化过程。在快原子轰击（FAB）质谱中，由该过程产生的离子比赖氨酸或其他含胺残基的C端侧碎片化产生的酰鎓型B离子低16 Da。这些离子被称为（B - 16）离子，可用于在肽质谱中区分同量异位氨基酸赖氨酸和谷氨酰胺。高分辨率测量表明，（B - 16）离子与相应的B离子在组成上的差异是通过去除一个氧原子实现的。据信其形成是通过赖氨酸侧链的游离氨基对酰鎓离子（B离子）的碳进行亲核攻击引发的环化过程发生的。直接从质子化肽开始的类似环化过程也可能发生。由于谷氨酰胺残基的亲核性比赖氨酸相对较弱（即酰胺与胺相比），因此类似的环化过程对谷氨酰胺受到限制。尽管在高能碰撞诱导解离下已检测到（B - 16）离子，但它们的形成不如通过FAB质谱法那样容易。本文提出了一种与该观察结果以及其他实验证据一致的机制，以解释（B - 16）离子的形成。
