Fragmentation in matrix-assisted laser desorption ionization : dissociation reactions of [M+Cu]+ peptide ions /
Peptide-Cu⁺ complexes are studied by metestable ion dissociation in matrix-assisted laser desorption ionization (MALDI) mass spectrometry. The Cu⁺ ion is introduced into the gas-phase by direct sample deposition and desorption from a copper sample stage with UV laser irradiation. Studies using varia...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=733039651&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Peptide-Cu⁺ complexes are studied by metestable ion dissociation in matrix-assisted laser desorption ionization (MALDI) mass spectrometry. The Cu⁺ ion is introduced into the gas-phase by direct sample deposition and desorption from a copper sample stage with UV laser irradiation. Studies using variable laser wavelengths for desorption are used to probe attachment mechanics of the Cu⁺ ion to the organic matrix and reptiles. The results of these experiments suggest the Cu⁺ ion complexes with the matrix and analyse in the sample, not as a gas-phase ion-molecule reaction. The systems studied include pepsines with basic amino acids, specifically, reptiles containing an N-terminal arginine, a C-terminal arginine, and arginine as an internal amino acid. The Cu⁺ ion binding sites are determined by the fragmentation chemistry of the [M+Cu]⁺ peptide ions. Arginine anchors the Cu⁺ ion in most [M+Cu]⁺ peptide ions, but histidine and lysine also readily bind the Cu⁺ ion depending on their position in the peptide chain. That is, on the basis of the metestable ion abundances from [M+Cu]⁺ ions the relative Cu-b ion affinity of arginine, histidine, and lysine varies from a position as the N-terminal amino acid to the C-terminal amino acid. The fragmentation of protonated peptides has been extensively studied by mass spectrometry and the fragmentation reactions of the [M+Cu]⁺ ions are compared to those of the [M+H]⁺ ions. Two types of metastable ions of the [M+Cu]⁺ ions are observed that are seldom, if ever, observed in the dissociation of [M+H]⁺ ions. The fragmentation mechanisms for formation of these unique metastable ions are proposed. Cleavage of the peptide backbone amide bond is commonly observed in [M+Cu]⁺ ions and [M-H]⁺ ions; however, based on hydrogen/deuterium exchange experiments the mechanisms of formation for these fragment ions are distinctly different. Once the binding site and fragmentation mechanisms are discerned, the overall gas-phase structure(s) of the [M+Cu]⁺ ions are determined. One distinguishing gas-phase structure that we propose for [M+Cu]⁺ peptide ions containing a C-terminal arginine is that of a zwitterion where a protonated guanidine of arginine interacts through a salt-bridge with the deprotonated carboxylic acid C-terminus. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xviii, 204 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 195-203). |