Fragmentation Pathways Of Metal-Peptide Complex In Mass Spectrometry

The identification of proteins is one of the most basic content in proteomics, and it is very important for the accurate determination of the primary structure constructed by amino acid sequence. Rapid development in life sciences, genomics and proteomics is greatly promoted by the invention of electrospray ionization source (ESI), matrix-assisted laser-desorption ionization (MALDI) and tandem mass spectrometry technology. Trypsin digestion combined with high performance liquid chromatography-mass spectrometry (LC-MS) as well as database search have become the conventional means for identification of the protein sequence, however, a high rate of false-positive protein identification may occur due to imperfection of current search softwares. A well understanding of peptide fragmentation pathways will benefit manual analysis of a mass spectrum, at the same time, it combined with software algorithms will greatly improve the accuracy of protein identification. Therefore, many foreigner research groups have made effort on study of peptide fragmentation mechanism and put forward a "mobile-proton model", which is helpful in the interpretation of fragmentation pathways of protonated peptides. Metal ions play an important role in organism that interact with peptide different from protons. In this thesis, we focused on fragmentation pathways of metal-peptide complex and did work as follows:.First of all, fragmentation patterns of eight pairs of sodium associated heptapeptides that contain α-or β-Asp residues in2nd and6th amino acid positions, respectively, are studied by electrospray ion trap mass spectrometer. We succeed in identification the isomers by the diagnostic peak. Formation mechanisms of most product ions are described.Secondly, fragmentation patterns of a deuterohemin containing peptide DhHP-6 (deuterohemin-β-AHTVEK-NH2) were studied in detail. Various product ions generated in different charge state (+1,+2,+3) of the peptide were described. In particular, a series of characteristic product ions like:bn-44, cn and bn+18were observed. The bn-44ion was seldom reported. Many additional experiments were designed to find the factors that result in the generation of bn-44ions. The results indicate that the neutral loss of44may have a close relationship with the oxazolone structure in the C-terminus of b ions. Complex rearrangement may occur for the generation of cn and bn+18ions, which is unusual in low-energy of collision induced dissociation (CID) mode.In third work, peptide radical cations of the peptide DhHP-6were detected and the factors effect on their formation were explored. Many diseases could be induced by the presence of metal or radicals. We hope that peptide radical studies could be helpful for the disease analysis.