Abstract
Tryptic digest of lysozyme was analyzed by MALDI-TOF/TOF mass spectrometry.Six unique peptides were identified with high confidence by database searching and the Mascot score was 420 with the protein coverage of 54%.Furthermore,several uncommon modifications including deamidation of asparagines(Asp) residue,deamidation of Asp plus oxidation of methionine(Met),deamidation of Asp plus oxidation of Met plus oxidation of Trp were observed for peptide 98IVSDGDGMNAWVAWR112.Furthermore,a dehydration reaction was observed in the process of MALDI for this peptide.All above results showed that the Asparagine at 103rd position had a highly chemical reactivity.In addition,the modification of propionamide(Cystine) was observed for another two peptides.This study indicated that,for those of unmatched data by database searching,the data utilization and the certainty of analysis result would be increased by using manual explantation and selecting very low abundant ions in primary spectrum and this method was also helpful for finding potential post-translational modifications.
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