| The histidine effect. Electron transfer and capture cause different dissociations and rearrangements of histidine peptide cation-radicals. | |
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MedLine Citation:
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PMID: 20681705 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Electron-transfer and -capture dissociations of doubly protonated peptides gave dramatically different product ions for a series of histidine-containing pentapeptides of both non-tryptic (AAHAL, AHAAL, AHADL, AHDAL) and tryptic (AAAHK, AAHAK, AHAAK, HAAAK, AAAHR, AAHAR, AHAAR, HAAAR) type. Electron transfer from gaseous Cs atoms and fluoranthene anions triggered backbone dissociations of all four N-C(alpha) bonds in the peptide ions in addition to loss of H and NH(3). Substantial fractions of charge-reduced cation-radicals did not dissociate on an experimental time scale ranging from 10(-6) to 10(-1) s. Multistage tandem mass spectrometric (MS(n)) experiments indicated that the non-dissociating cation-radicals had undergone rearrangements. These were explained as being due to proton migrations from N-terminal ammonium and COOH groups to the C-2' position of the reduced His ring, resulting in substantial radical stabilization. Ab initio calculations revealed that the charge-reduced cation-radicals can exist as low-energy zwitterionic amide pi* states which were local energy minima. These states underwent facile exothermic proton migrations to form aminoketyl radical intermediates, whereas direct N-C(alpha) bond cleavage in zwitterions was disfavored. RRKM analysis indicated that backbone N-C(alpha) bond cleavages did not occur competitively from a single charge-reduced precursor. Rather, these bond cleavages proceeded from distinct intermediates which originated from different electronic states accessed by electron transfer. In stark contrast to electron transfer, capture of a free electron by the peptide ions mainly induced radical dissociations of the charge-carrying side chains and loss of a hydrogen atom followed by standard backbone dissociations of even-electron ions. The differences in dissociation are explained by different electronic states being accessed upon electron transfer and capture. |
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Authors:
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Frantisek Turecek; Thomas W Chung; Christopher L Moss; Jean A Wyer; Anneli Ehlerding; Anne I S Holm; Henning Zettergren; Steen Brøndsted Nielsen; Preben Hvelplund; Julia Chamot-Rooke; Benjamin Bythell; Béla Paizs |
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Publication Detail:
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Type: Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S. |
Journal Detail:
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Title: Journal of the American Chemical Society Volume: 132 ISSN: 1520-5126 ISO Abbreviation: J. Am. Chem. Soc. Publication Date: 2010 Aug |
Date Detail:
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Created Date: 2010-08-04 Completed Date: 2010-11-23 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 7503056 Medline TA: J Am Chem Soc Country: United States |
Other Details:
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Languages: eng Pagination: 10728-40 Citation Subset: IM |
Affiliation:
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Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA. turecek@chem.washington.edu |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Cations
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chemistry Computer Simulation Electrons* Free Radicals / chemistry Histidine / chemistry* Peptides / chemistry* Protein Conformation |
| Chemical | |
Reg. No./Substance:
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0/Cations; 0/Free Radicals; 0/Peptides; 71-00-1/Histidine |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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