中文摘要：

利用基质辅助激光解吸电离-串联飞行时间质谱（MALDI—TOF／TOF）高置信度地鉴定了枯草芽孢杆菌中的蛋白酶抑制剂和杆菌肽F两种蛋白及其翻译后修饰，发现在这两种蛋白质中共有5个肽段发生谷氨酸甲基化，其中肽段FELVVYDsEHK存在FE（Methylation）LVVYDSEHK和FELVVYDSE（Methylation）HK两种形式。结果表明，MALDI—TOF／TOF高能CID所提供的丰富断裂信息和全质量范围扫描对提高分析结果的确定性具有重要作用。此外，这5个甲基化肽段都可以检测到相对含量更高的非甲基化肽段，这为降低分析结果的假阳性提供了辅助判据。在低质量区检测到甲基化赖氨酸的亚胺相关离子m／z98和143，说明发生了赖氨酸的甲基化；检测到m／z116则提示发生了谷氨酸甲基化。

英文摘要：

The separated intracellular proteinase inhibitor and bacillopeptidase F of Bacillus subtilis subsp. were identified by MALDI-TOF/TOF mass spectrometry with high confidence. Furthermore, a total of five peptides concerning methylation of glutamic acid were found by a protein database search and manual explanation, specially, two individual methylation sites of glutamic acid were detected for peptide FELVVYDSEHK. Our results indicated that MALDI-TOF/TOF high energy CID played an important role in the identification of glutamate methylation because it provided abundant fragment information and the full range mass scanning, which improved the certainty of analytical results. In addition, we found the five methylated peptides were always detected simultaneously with their non-methylated analogue and with lower abundance, which indicated that the methylated protein was only a small portion of the total protein. This fact can be used to judge the false positive identification of peptide methylation. Finally, the immonium ion of methylated glutamate at m/z 116 also could provide a clue for this modification compared with the immonium related ion of methylated lysine at m/z 98 and m/z 143.