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Direct identification of intramolecular disulfide links in peptides using negative ion electrospray mass spectra of underivatised peptides. A joint experimental and theoretical study
Author(s) -
Bilusich Daniel,
Maselli Vita M.,
Brinkworth Craig S.,
Samguina Tatiana,
Lebedev Albert T.,
Bowie John H.
Publication year - 2005
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2149
Subject(s) - chemistry , intramolecular force , ion , cleavage (geology) , mass spectrum , peptide , disulfide bond , crystallography , computational chemistry , stereochemistry , organic chemistry , biochemistry , geotechnical engineering , fracture (geology) , engineering
[MH] − parent anions of underivatised peptides containing an intramolecular disulfide bridge undergo characteristic loss of the elements of H 2 S 2 , a process diagnostic of the presence of the disulfide moeity. This facile process is initiated from a side‐chain enolate anion. Theoretical calculations (at the HF/6‐31G(d)//AM1 level of theory) indicate that the process is exothermic with a small barrier. When the disulfide link involves a C‐terminal Cys, the negative ion spectrum shows an [(MH)(H 2 S 2 +CO 2 )] fragment anion which is usually the main peak of the spectrum. This process is also directed by an enolate anion: theoretical calculations suggest a stepwise sequence with loss of CO 2 preceding loss of H 2 S 2 . Both [(MH)H 2 S 2 ] and [(MH)(H 2 S 2 +CO 2 )] anions undergo backbone cleavage allowing identification of the amino acid sequence of the peptide. Copyright © 2005 John Wiley & Sons, Ltd.