Cu(II) ION TRANSFER FROM PEPTIDES TO CYSTEINE. FORMATION OF THE TERNARY COMPLEX, (CYSTEINE)-Cu(II)-(PEPTIDE), AS AN INTERMEDIATE

The transfer of Cu(II) ion from glycine peptides to cysteine was studied by a stopped-flow spectrophotometric method. The first reaction is the ligand substitution of Cu(II)-peptide, Cu(H−2peptide)−, by cysteine forming the ternary complex, (cysteine)Cu(H−1peptide)2−. The subsequent reaction is the nucleophilic attack of cysteine upon the ternary complex producing Cu(II)-biscysteinate. The rate of those reactions depends on the steric factors around the metal site.