Gas phase studies of the interactions of Fe2+ with cysteine-containing peptides

Gas-phase complexes of cysteine-containing peptides and Fe2+ were produced by fast atom bombardment and studied by tandem mass spectrometry. Specific and strong interactions of the iron acid sulfur from the thiol group of the cysteine side chain are preserved in the gas phase acid are the basis for highly specific fragmentation to give abundant [a(n) - 2H + Fe](+) ions, where n is position of the cysteine residue from the N-terminus of peptide. Metal/peptide complexes containing more than one Cys residue were also investigated; they display similar chemistry upon collisionally activated decompositions, indicating that the Fe ion primarily binds at cysteine sites. (C) 1998 American Society for Mass Spectrometry.