title: Spectroscopic properties of the alpha fragment of metallothionein.
abstract: Absorption, CD, and magnetic circular dichroism spectra are reported for the alpha fragment of rat liver Cd,Zn-metallothionein (MT) 2. The CD and magnetic circular dichroism spectra of the Cd4 cluster unit are particularly well-resolved and are remarkably similar to data of the complete Cd,Zn-MT. It is suggested that the high signal intensity in the 225 nm CD band may be attributed to an interaction between a terminal amino acid residue and the Cd4 cluster. Titration experiments with CdCl2 and [Cu(CH3CN)4]+ show that while no additional Cd2+ can be bound in the presence of excess Cd2+, Cu+ does replace the bound Cd2+ in a complex reaction to form at least two species. One of these species requires the presence of both Cu+ and Cd2+, with a stoichiometry of Cu 3.0, Cd 2.5. Further, Cu+ displaces all the remaining Cd2+, and the spectra recorded now closely resemble Cu-MT formed by titration of Cd,Zn-MT with greater than 8 mol eq of Cu+.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D008099:Liver / Q000378:metabolism*; D008668:Metallothionein / Q000302:isolation & purification*; D010446:Peptide Fragments / Q000032:analysis; D011487:Protein Conformation; D051381:Rats; D013056:Spectrophotometry, Ultraviolet; D013381:Subtilisins
chemical_list: D000596:Amino Acids; C041582:Cd-Zn-metallothionein; D010446:Peptide Fragments; D008668:Metallothionein; D013381:Subtilisins