Zinc ( I 1 ) and Copper ( I 1 ) Binding to Serum Albumin

Metal binding strategies employing low molecular weight chelators and equilibrium dialysis were used to investigate several unresolved aspects of zinc and copper binding to serum albumin. Direct measurement of histidine binding to bovine serum albumin when the histidine is presented either as a metal-chelate or alone provides no evidence for an albumin-metal-histidine ternary complex. Using previously determined intrinsic constants for Zn(I1) and Cu(II), we have measured zinc binding to bovine serum albumin in the presence of saturating amounts of copper. The results of these experiments unambiguously show that zinc and copper bind at separate noninteracting sites on this protein. The intrinsic constants for zinc and copper binding to dog serum albumin have been determined. Contrary to previous reports, we find that dog serum albumin has a specific high affinity site for copper, logl,$ 10.17 for Cu(I1) compared to 6.85 for Zn(I1) at the separate site.