COMPLEXES OF SILVER(I) WITH PEPTIDES AND PROTEINS AS PRODUCED IN ELECTROSPRAY MASS-SPECTROMETRY

Silver(I) forms aqueous phase complexes with both sulfur and nonsulfur containing peptides and proteins. These complexes were introduced int o the gas phase via electrospray, and their structures probed by means of tandem mass spectrometry. Experiments with di-, tri-, and oligopep tides show that the abundance of silver(I)-containing ions increases r elative to that of proton-containing ions as peptide length increases. This increase is much more dramatic for methionine-containing peptide s. Collision-induced dissociation of silver-peptide complexes yields a multitude of product ions that are silver containing. However, even f or methionine-containing peptides, very few of these product ions cont ain the methionine residue. The solution-phase structure and the gas-p hase structure of the silver/peptide complex are not identical. The me thionine sulfur acts as the silver anchoring point in solution. Desolv ation in the gas phase leads to a rearrangement of the silver/peptide complex such that the silver ion becomes chelated to the nitrogen and oxygen atom on the peptide backbone in addition to the methionine sulf ur. This rearrangement decreases the importance of the silver/sulfur b ond to the extent that it is frequently broken upon collision activati on and leads to the formation of silver/peptide product ions that are nonsulfur bearing. Crown copyright 1997.