中文摘要：

完全从头测序要求区分肽段中的同量异序氨基酸谷氨酰胺和赖氨酸,而这通常需要借助高分辨质谱.谷氨酰胺和赖氨酸都可以产生m/z 101亚胺离子和m/z 84亚胺相关离子,尽管已知赖氨酸亚胺离子m/z 101有时强度较弱,以及m/z 84离子可预示赖氨酸的存在,但该特征能否用于区分赖氨酸和谷氨酰胺仍存在争议.本工作以合成肽段和蛋白质胰酶水解肽段为研究体系,利用基质辅助激光解吸电离的高能碰撞诱导解离模式产生的亚胺及其相关离子的相对强度区分这两种氨基酸.结果表明：谷氨酰胺更易产生m/z 101离子,而赖氨酸更易产生m/z 84和m/z 129离子.对于不同时含有赖氨酸和谷氨酰胺的肽段,使用m/z 84离子与亚胺离子m/z 101的相对强度比值,而非它们的绝对强度,以及m/z 101离子的测量值,可以直接判断序列中存在的是赖氨酸还是谷氨酰胺.对于含有谷氨酰胺,并以赖氨酸结尾或含有漏切赖氨酸的肽段,该强度比可为序列中谷氨酰胺的个数和位置提供参考.因此,低质量区提供的亚胺及其相关离子信息有助于区分赖氨酸和谷氨酰胺.

英文摘要：

Differentiation of isobaric glutamine （Gin） and lysine （Lys） is needed for complete de novo sequencing and require high resolution mass spectrometry generally. Both Gin and Lys can produce immonium ions at m/z 101 and their related ions at m/z 84. Although it is known that the peak at m/z 101 due to Lys is sometimes weak and abundant ions at m/z 84 is a good indicator of the presence of Lys, whether this feature can be used to discriminate Lys and Gln is still a controversial issue. In this study, investigations were used to distinguish Gln and Lys based on immonium and immonium-related ions produced by matrix-assisted laser desorption ionization tandem time-of flight （MALDI-TOF/TOF） withhigh energy collision induced dissociation （CID）. The work focused on a series of synthetic peptides and 184 tryptic peptides. The result shows that Gin is more prone to generate immonium ions at m/z 101comparede to Lys, which generates m/z 84 and m/z 129 ions main- ly. It is the ratios of intensity of m/z 101 ion versus m/z 84, rather than the intensity value of them, can be used to distinguish Gln versus Lys for practical samples for those peptides that containing Lys or Gln, or provide clue for the number and position of Gln for Lys-terminated peptides. Additionally, the mass measurement at m/z 101 is also relevant for distinguishing Lys and Gln. This observation has demonstrated that the usefulness of low mass region information of TOF/TOF spectra in distinguishing isobaric Lys and Gln.