title: Information on metal binding properties of metallothioneins from optical spectroscopy.
abstract: Absorption, circular dichroism and emission measurements made during titrations of rabbit liver Zn-MT and calf liver Cu, Zn-MT with Cd2+ and Cu+ are reported. There are systematic changes in the CD and emission spectra that can be associated with the formation of several species during these titrations. Addition of Cu+ to Zn-MT results in the formation of distinct species that form at specific stoichiometries, these are: Cu6-MT, Cu12-MT and Cu20-MT. The emission intensity due to Cu+ provides a sensitive indication of the presence of Cu-S clusters for the Cu6-MT and Cu12-MT species, suggesting that Cu6-Sx clusters form in both the alpha and beta domains of the protein. The data also demonstrate that Cd7-MT will bind 12 Cu+ to form a species with the stoichiometry of 12 Cu: 4 Cd, and that, surprisingly, Cu12-MT will also bind Cd2+ to form this same new species. It is suggested that the new species incorporates a Cu6 cluster in the beta domain and a mixed-metal Cu6, Cd4 cluster in the alpha domain.
mesh_terms: D000818:Animals; D002104:Cadmium / Q000378:metabolism*; D002417:Cattle; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism*; D008099:Liver / Q000032:analysis; D008668:Metallothionein / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D013053:Spectrophotometry; D015032:Zinc / Q000378:metabolism
chemical_list: D002104:Cadmium; D003300:Copper; D008668:Metallothionein; D015032:Zinc