Reversible hydrogen transfer reactions of cysteine thiyl radicals in peptides: the conversion of cysteine into dehydroalanine and alanine, and of alanine into dehydroalanine

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Issue Date
2011-10-27Author
Mozziconacci, Olivier
Kerwin, Bruce A.
Schöneich, Christian
Publisher
American Chemical Society
Type
Article
Article Version
Scholarly/refereed, author accepted manuscript
Rights
This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1029/2010GC003479.
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The photodissociation of disulfide bonds in model peptides containing Ala and Ala-d3 generates a series of photoproducts following the generation of a CysS• thiyl radical pair. These photoproducts include transformations of Cys to dehydroalanine (Dha) and Ala, as well as Ala to Dha. Intramolecular Michael addition of an intact Cys with a photolytically generated Dha results in the formation of cyclic thioethers. The conversion of Cys into Dha likely involves a 1,3-H-shift from the Cys αC-H bond to the thiyl radical, followed by elimination of HS•. The conversion of Dha into Ala most likely involves hydrated electrons, which are generated through the photolysis of Cys, the photoproduct of disulfide photolysis. Prior to stable product formation, CysS• radicals engage in reversible hydrogen transfer reactions with αC-H and βC-H bonds of the surrounding amino acids. Especially for the βC-H bonds of Ala such hydrogen transfer reactions are unexpected based on thermodynamic grounds; however, the replacement of deuterons in Ala-d3 by hydrogens in H2O provides strong experimental evidence for such reactions.
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Citation
Mozziconacci, O., Kerwin, B. A., & Schöneich, C. (2011). Reversible hydrogen transfer reactions of cysteine thiyl radicals in peptides: the conversion of cysteine into dehydroalanine and alanine, and of alanine into dehydroalanine. The Journal of Physical Chemistry. B, 115(42), 12287–12305. http://doi.org/10.1021/jp2070453
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