title: The role of copper in cysteine oxidation: study of intra- and inter-molecular reactions in mass spectrometry.
abstract: Cysteine-containing peptide oxidation was studied both by using an inert platinum electrode and a sacrificial electrode (copper or zinc) generating metallic ions in electrospray ionization mass spectrometry (ESI-MS). Using peptides containing one, two and three cysteines, we have compared the different chemical and electrochemical oxidation pathways of cysteine (RS(-II)H) to cystine (RS(-I)S(-I)R) and to sulfenic, sulfinic and sulfonic acid (RS(0)OH, RS(II)O(2)H and RS(IV)O(3)H, respectively). In the absence of copper ions, intra-molecular reactions were the most abundant, whereas inter-molecular reactions were found to be enhanced by the presence of copper ions. These cations favor the formation of 2 : 1 (peptide : copper) complexes compared to 1 : 1 complexes, thus enhancing the formation of inter-molecular bridges. This study highlights the importance of the position of cysteine inside a peptide during disulfide bridge formation.
authors.affiliation: Laboratoire d'Electrochimie Physique et Analytique, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Prudent
authors.forename: Hubert H
authors.initials: HH
authors.lastname: Girault
mesh_terms: D000595:Amino Acid Sequence; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D003553:Cystine / Q000737:chemistry / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D004566:Electrodes; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010984:Platinum; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013456:Sulfur Acids / Q000737:chemistry / Q000378:metabolism
chemical_list: D004220:Disulfides; D010455:Peptides; D013456:Sulfur Acids; D003553:Cystine; D010984:Platinum; D003300:Copper; D003545:Cysteine