Comparative luminescence of rat liver Cu-thionein and its chemically synthesized alpha-domain

A peptide corresponding to the alpha-domain of rat liver metallothionein-2 was chemically synthesized employing the solid phase peptide synthesis technique. Its luminescence properties that depend on the coordinated Cu(I) have been studied using luminescence spectrometric titration in the presence of Cu(I). Unlike the intact metallothionein which has been converted into the Cu species, the emission and excitation spectra of the Cu-alpha-fragment showed a red shift by 20 nm and 65 nm, respectively, suggesting a more compact and stable luminophore in the alpha-domain. Saturation of Cu(I) coordination was reached in the presence of 6.5 mol eq Cu(I) when the alpha-fragment was used and 12 mol eq Cu(I) were specifically bound by the intact metallothionein. The emission bands were homogeneous and no decline of the cluster structure was observed when excessive Cu(I) was added after saturation. A rearrangement of the Cu-cluster in metallothionein during its formation seems to be plausible.