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HEAVY METAL BINDING TO PEPTIDES AT HIGHER pH: NOVEL ESI-MS APPROACH
Abstract
The stoichiometry of metal?protein complexes is pH dependent. Since mass spectrometric measurements at higher pH values are difficult in the presence of usual buffers, we extended this approach to pH in excess of 10 by adding ethanolamine to the electrospray solution being investigated. Therefore, a new method for probing the metal ion-peptide complexes at high pH utilizing electrospray ionization mass spectrometry (ESI-MS) has been advanced. Nevertheless, the high pH ESI-MS spectra of peptides are far too complex for interpretation as most of the signals overlap heavily. Therefore, new strategies have been introduced to identify the characteristic signals for some important metal ion-peptide complexes in the spectra recorded at high pH or high concentrations of metal ions. The following peptides are used in this study: tetraglycine, glutathione, and ?-amyloid peptides and their fragments. On forming coordination compounds of peptides such as glutathione or ?-amyloid fragments with copper or other heavy metal ions the resulted spectra become complicated showing characteristic signals for a large variety of multiply charged metal ion adducts of peptide oligomers. On increasing the concentration of metal ions or pH, multi ion-peptide oligomers are formed. The fragmentation of metal-peptide complex ions, whose peaks in the spectrum are foreseen by calculation, may offer information on their structure. Ethanolamine did not interfere with the mass spectrometry analysis. Several applications of ESI-MS are discussed, including amyloid peptide interactions with metal ions. In brief, new MS strategies have been proposed to determine the stoichiometry of metal binding at higher pH. The MS and MS/MS spectra are of both biological and analytical or toxicological interest.
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