INFLUENCES OF PEPTIDE SIDE-CHAINS ON THE METAL-ION BINDING-SITE IN METAL ION-CATIONIZED PEPTIDES - PARTICIPATION OF AROMATIC RINGS IN METALCHELATION

Aromatic side chains on amino acids influence the fragmentations of ca tionic complexes of doubly charged metal ions and singly deprotonated peptides. The metal ion interacts with an aromatic side chain and bind s to adjacent amide nitrogens. When fragmentation occurs, this bonding leads to the formation of abundant metal-containing a-type ions by re actions that occur at the sites of amino acids that contain the aromat ic side chain. Furthermore, formation of metal-containing immonium ion s of the amino acids that contain the aromatic side chain also are for med. The abundant a-type ions may be useful in interpretation strategi es in which it is necessary to locate in a peptide the position of an amino acid that bears an aromatic side chain.