A peptide molecule mimicking the copper(II) transport site of human serum albumin. A comparative study between the synthetic site and albumin.

Diglycyl-L-histidine is a peptide molecule designed to mimic the specific Cu(II) transport site of human albumin. The equilibria involved in the Cu(II)-diglycyl-L-histidine system have been investigated by analytical potentiometry in aqueous solution (0.15 M NaCl, 25’). The synthetic peptide molecule bound Cu(I1) exclusively as a 1: I complex in the pH range of 6.50 to 11.00. The results further showed that the complex has the same ligand atoms binding to Cu(I1) as those suggested for the specific Cu(I1) binding site of human albumin. The interaction of peptide with Cu(I1) in the presence of albumin, studied by equilibrium dialysis at pH 7.53 and ionic strength 0.16, indicates that this tripeptide is able to compete with albumin for Cu(I1). The dissociation constant of the Cu(II)-peptide complex has a value of 1.18 x lo-r6 as compared with 6.61 X lo-r7 for Cu(II)-albumin. The lower Cu(I1) binding strength of the peptide may reflect the influence of either the COOH-terminal free carboxy1 group of the peptide or the side chain residues of the Cu(II) binding site in the native protein or both. In the presence of equimolar concentrations of albumin and peptide, and approximately 20-fold excess of L-histidine, there is about 18% of Cu(I1) present in the forms of Cu(II)-albumin