Nagoshi Keishiro, Yamakoshi Mariko, Sakamoto Kenya, Takayama Mitsuo
Mass Spectrometry Laboratory, Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan.
J Am Soc Mass Spectrom. 2018 Jul;29(7):1473-1483. doi: 10.1007/s13361-018-1958-2. Epub 2018 Apr 19.
Radical-driven dissociation (RDD) of hydrogen-deficient peptide ions [M - H + H] has been examined using matrix-assisted laser dissociation/ionization in-source decay mass spectrometry (MALDI-ISD MS) with the hydrogen-abstracting matrices 4-nitro-1-naphthol (4,1-NNL) and 5-nitrosalicylic acid (5-NSA). The preferential fragment ions observed in the ISD spectra include N-terminal [a] + ions and C-terminal [x], [y + 2], and [w] ions which imply that β-carbon (Cβ)-centered radical peptide ions [M - Hβ + H] are predominantly produced in MALDI conditions. RDD reactions from the peptide ions [M - Hβ + H] successfully explains the fact that both [a] and [x] ions arising from cleavage at the Cα-C bond of the backbone of Gly-Xxx residues are missing from the ISD spectra. Furthermore, the formation of [a] ions originating from the cleavage of Cα-C bond of deuterated Ala(d3)-Xxx residues indicates that the [a] ions are produced from the peptide ions [M - Hβ + H] generated by deuteron-abstraction from Ala(d3) residues. It is suggested that from the standpoint of hydrogen abstraction via direct interactions between the nitro group of matrix and hydrogen of peptides, the generation of the peptide radical ions [M - Hβ + H] is more favorable than that of the α-carbon (Cα)-centered radical ions [M - Hα + H] and the amide nitrogen-centered radical ions [M - H + H], while ab initio calculations indicate that the formation of [M - Hα + H] is energetically most favorable. Graphical Abstract ᅟ.
使用基质辅助激光解吸/电离源内衰变质谱法（MALDI-ISD MS），以夺氢基质4-硝基-1-萘酚（4,1-NNL）和5-亚硝基水杨酸（5-NSA），研究了缺氢肽离子[M - H + H]的自由基驱动解离（RDD）。在ISD光谱中观察到的优先碎片离子包括N端[a]+离子和C端[x]、[y + 2]和[w]离子，这表明以β-碳（Cβ）为中心的自由基肽离子[M - Hβ + H]在MALDI条件下主要生成。肽离子[M - Hβ + H]的RDD反应成功解释了ISD光谱中缺少Gly-Xxx残基主链Cα-C键断裂产生的[a]和[x]离子这一事实。此外，源自氘代Ala(d3)-Xxx残基Cα-C键断裂的[a]离子的形成表明，[a]离子是由从Ala(d3)残基夺氘产生的肽离子[M - Hβ + H]产生的。从基质的硝基与肽的氢之间直接相互作用夺氢的角度来看，肽自由基离子[M - Hβ + H]的生成比以α-碳（Cα）为中心的自由基离子[M - Hα + H]和以酰胺氮为中心的自由基离子[M - H + H]更有利，而从头算计算表明[M - Hα + H]的形成在能量上最有利。图形摘要ᅟ。
