Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Canada.
J Am Soc Mass Spectrom. 2011 May;22(5):906-11. doi: 10.1007/s13361-011-0091-2. Epub 2011 Mar 8.
The product ion mass spectra resulting from collisional activation of doubly-protonated tryptic-type peptides Ala-Ala-Xaa-Ala-Ala-Ala-Arg have been determined for Xaa = Ala(A), Ser(S), Val(V), Thr(T), Ile(I), Phe(F), Tyr(Y), Sar, Met(M), Trp(W), Pro(P), and Gln(Q). The major fragmentation reaction involves cleavage of the second amide bond (counting from the N-terminus) except for Xaa = Ser and Thr where elimination of H(2)O from the M + 2H ion forms the base peak. In general, the extent of cleavage of the second amide bond shows little dependence on the identity of Xaa and little dependence on whether the bond cleavage involves symmetrical bond cleavage to form a y(5)/b(2) ion pair or asymmetrically to form y (5) (+2) and a neutral b(2) species. Notable exceptions to this generalization occur for Xaa equal to Pro or Sar. For Xaa = Pro only cleavage of the second amide bond is observed, consistent with a pronounced proline effect, i.e., cleavage N-terminal to Pro. When Xaa = Sar considerably enhanced cleavage of the second amide bond also is observed, suggesting that at least part of the proline effect relates to the tertiary nature of the amide nitrogen. In the competition between symmetric and asymmetric bond cleavage an attempt to establish a linear free energy correlation in relating ln(y(5)(+2)/y(5)) to PA(H-Xaa-OH) did not lead to a reasonable correlation although the trend of increasing y(5)(+2)/y(5) ratio with increasing proton affinity of H-Xaa-OH was clear. Proline showed a unique behavior in giving a much higher y(5)(+2)/y(5) ratio than any of the other residues studied.
经碰撞诱导双重质子化胰蛋白酶型肽 Ala-Ala-Xaa-Ala-Ala-Ala-Arg 的碰撞激活产生的产物离子质谱已确定 Xaa = Ala(A)、Ser(S)、Val(V)、Thr(T)、Ile(I)、Phe(F)、Tyr(Y)、Sar、Met(M)、Trp(W)、Pro(P)和 Gln(Q)。主要的断裂反应涉及从 N 末端计数的第二个酰胺键的断裂，但 Xaa = Ser 和 Thr 除外，其中从 M + 2H离子中消除 H(2)O 形成基峰。一般来说，第二个酰胺键的断裂程度对 Xaa 的身份几乎没有依赖性，也几乎没有依赖性，键断裂是否涉及形成 y(5)/b(2)离子对的对称键断裂或不对称地形成 y(5)(+2)和中性 b(2)物种。这种概括的明显例外发生在 Xaa 等于 Pro 或 Sar 时。对于 Xaa = Pro，仅观察到第二个酰胺键的断裂，这与明显的脯氨酸效应一致，即脯氨酸 N 末端的断裂。当 Xaa = Sar 时，也观察到第二个酰胺键的明显增强断裂，这表明脯氨酸效应的至少一部分与酰胺氮的三级性质有关。在对称和不对称键断裂之间的竞争中，试图建立一个线性自由能相关关系，将 ln(y(5)(+2)/y(5))与 PA(H-Xaa-OH)联系起来，并没有导致一个合理的相关性，尽管 y(5)(+2)/y(5)比值随 H-Xaa-OH 的质子亲和力增加的趋势是明显的。脯氨酸的行为非常独特，其 y(5)(+2)/y(5)比值比研究的任何其他残基都高得多。
