Harrison Alex G, Young Alex B
Department of Chemistry, University of Toronto, Toronto, Canada.
J Mass Spectrom. 2005 Sep;40(9):1173-86. doi: 10.1002/jms.891.
The collision-induced dissociation (CID) fragmentation reactions of a variety of deprotonated peptides containing proline have been studied in detail using MS(2) and MS(3) experiments, deuterium labelling and accurate mass measurements when necessary. The M--H--CO(2) (a(2)) ion derived from H-Pro-Xxx-OH dipeptides shows an unusual fragmentation involving loss of C(2)H(4); this fragmentation reaction is not observed for larger peptides. The primary fragmentation reactions of deprotonated tripeptides with an N-terminal proline are formation of a(3) and y(1) ions. When proline is in the central position of tripeptides, a(3), y(2) and y(1) ions are the primary fragmentation products of M--H, while when the proline is in the C-terminal position, a(3)and y(1) ions are the major primary products. In the latter case, the a(3) ion fragments primarily to the ''b(2) ion; further evidence is presented that the ''b(2) ions have a deprotonated oxazolone structure. Larger deprotonated peptides having at least two amino acid residues N-terminal to proline show a distinct preference for cleavage of the amide bond N-terminal to proline to form, mainly, the appropriate y ion. This proline effect is compared and contrasted with the similar proline effect observed in the fragmentation of protonated peptides containing proline.
利用二级质谱（MS(2)）和三级质谱（MS(3)）实验，并在必要时采用氘标记和精确质量测量，对多种含脯氨酸的去质子化肽的碰撞诱导解离（CID）碎片化反应进行了详细研究。源自H-Pro-Xxx-OH二肽的M–H–CO₂ （a₂）离子显示出涉及乙烯（C₂H₄）损失的异常碎片化；对于更大的肽未观察到这种碎片化反应。N端为脯氨酸的去质子化三肽的主要碎片化反应是形成a₃和y₁离子。当脯氨酸处于三肽的中心位置时，a₃、y₂和y₁离子是M–H的主要碎片化产物，而当脯氨酸处于C端位置时，a₃和y₁离子是主要的初级产物。在后一种情况下，a₃离子主要碎片化形成“b₂离子；进一步的证据表明“b₂离子具有去质子化的恶唑酮结构。在脯氨酸N端至少有两个氨基酸残基的更大的去质子化肽显示出明显倾向于切割脯氨酸N端的酰胺键，主要形成相应的y离子。将这种脯氨酸效应与在含脯氨酸的质子化肽的碎片化中观察到的类似脯氨酸效应进行了比较和对比。
