Cordero M M, Houser J J, Wesdemiotis C
Department of Chemistry, University of Akron, Ohio 44325-3601.
Anal Chem. 1993 Jun 1;65(11):1594-601. doi: 10.1021/ac00059a019.
Collisionally activated dissociation (CAD) of the protonated polyalanines Ala-Ala,Ala-Ala-Ala, and Ala-Ala-Ala-Ala causes breakup of the peptide bonds leading to sequence-indicative fragment ions. The neutral molecules eliminated during these reactions are identified here using neutralization-reionization mass spectrometry (NRMS). N-terminal acylium ions (bn) arise after the C-terminus is lost as an intact amino acid or peptide; further loss of CO leads to immonium ions (an). Upon generation of C-terminal sequence ions (yn), a hydrogen atom attached to a nitrogen rearranges from the N-terminal to the C-terminal side yielding a protonated amino acid (y1) or peptide (y > or = 2) as the ionic fragment; the complementary neutral fragment is an aziridinone if the N-terminal amino acid is cleaved and a diketopiperazine if two N-terminal amino acid units are eliminated. Detection of neutral dissociation products can reveal valuable structure information, as demonstrated with the tetrapeptides Val-Gly-Ser-Glu and Val-Gly-Asp-Glu.
质子化聚丙氨酸（丙氨酸 - 丙氨酸、丙氨酸 - 丙氨酸 - 丙氨酸和丙氨酸 - 丙氨酸 - 丙氨酸 - 丙氨酸）的碰撞激活解离（CAD）会导致肽键断裂，产生指示序列的碎片离子。在此，利用中和再电离质谱法（NRMS）鉴定这些反应过程中消除的中性分子。C末端作为完整氨基酸或肽丢失后会产生N末端酰鎓离子（bn）；进一步失去CO会生成亚铵离子（an）。生成C末端序列离子（yn）后，与氮相连的氢原子从N末端重排到C末端，产生质子化氨基酸（y1）或肽（y≥2）作为离子碎片；如果N末端氨基酸被裂解，互补中性碎片是氮杂环丙烷酮；如果消除两个N末端氨基酸单元，互补中性碎片则是二酮哌嗪。如四肽缬氨酸 - 甘氨酸 - 丝氨酸 - 谷氨酸和缬氨酸 - 甘氨酸 - 天冬氨酸 - 谷氨酸所示，检测中性解离产物可揭示有价值的结构信息。
