On-line electrogeneration of copper-peptide complexes in microspray mass spectrometry

The role of copper in cysteine oxidation: study of intra- and inter-molecular reactions in mass spectrometry

“…These fragmentations were either related to peptide oxidation by Cu 2+ or by metastable ions. 13 This observation is identical for the multi-cysteine-containing peptides reported below. When Cu 2+ ions were added in solution and the experiments were performed with a Pt electrode (see ESIw), copper(I) ions were also observed.…”

“…This abundant dimer is present as multiply charged species: [2M 1 The electrooxidation of the Cu electrode produces either Cu 2+ or Cu + cations in solution. 13,37 These cations can here react with M 1 and 2M 1 . The addition of Cu + on M 1 (m/z = 872.2 Th) and on 2M 1 (m/z = 840.3 Th for z = 2 and m/z = 1679.3 Th for z = 1z) were the most abundant metal complexes observed.…”

“…Cu 2+ is an intermediate acid that prefers binding to intermediate ligands such as N-imidazole (histidine residue) and Cu + is a soft acid that prefers anchoring to soft ligands such as S-thiolate (cysteine residue) and also N-imidazole. 11 In mass spectrometry (MS), where ions are transferred from a liquid to a gas phase, the binding sites of Cu 2+ in proteins are identical 12,13 to those observed in solution, but arginine becomes the preferred anchorage for Cu + . [13][14][15] Cerda and Wesdemiotis noticed that the Cu + affinity for amino acids is increased when soft donor groups such as RSH are present compared to that of protons.…”

“…11 In mass spectrometry (MS), where ions are transferred from a liquid to a gas phase, the binding sites of Cu 2+ in proteins are identical 12,13 to those observed in solution, but arginine becomes the preferred anchorage for Cu + . [13][14][15] Cerda and Wesdemiotis noticed that the Cu + affinity for amino acids is increased when soft donor groups such as RSH are present compared to that of protons. 14 Mass spectrometry, especially coupled with an electrospray ionization (ESI) source, is a method of choice for studying biomolecules and their interactions with metal ions, as well as for studying peptide or protein oxidation.…”

“…13,37 Taking advantage of the electrochemical aspects of ESI, the complexation of copper ions, in different oxidation states, with non-cysteinyl peptides have been previously studied by using a sacrificial copper electrode. 13 Herein we study, with the same device, cysteine oxidation of peptides containing, one, two or three cysteines to compare the different oxidation pathways. The experiments were carried out first with a platinum electrode to observe the oxidation of the peptides per se, and then with a copper electrode to study the role of copper ions.…”