Interaction and coordination geometries for Ag(I) in the two metal sites of hemocyanin

Ag-111(I) perturbed angular correlations of gamma-rays (PAC) has been used to investigate the binuclear metal site of Ag-111(I)-substituted Carcinus a estuarii deoxyhemocyanin. The studies have shown that apo-hemocyanin is abl e to bind 2 mol of Ag(I) per mol of protein and that the binding is specifi c for the metal ion sites. The PAC spectra show pronounced changes when the stoichiometry of Ag(I) to protein is increased from 0.1 to 2.0. These chan ges have been interpreted as evidence of interactions between the two sites in terms of a structural destabilization of the first occupied site caused by the occupation of the second site. The experimental data for the Ag(I)- substituted metal sites do not agree well with the three-coordinated struct ure found in the Cu(I) holo-protein. However, if a water molecule is includ ed as a coordinating ligand in the Ag(I) metal site a successful interpreta tion of the experimental data can be obtained.