Spectroscopic studies, blue copper

A new line of research involving blue copper proteins deals with their unfolding and their structural heterogeneity. The thermal unfolding of amicyanin was studied with calorimetric and spectroscopic methods. It was found to be irreversible and the kinetic data were analyzed in a three state model. 

One of the major goals of studying active sites in copper proteins has therefore been to understand the spectroscopic features associated with the active site. This has led to a classification of three general types of copper protein active sites based on their unique spectral features Blue copper, normal copper and coupled binuclear copper. An additional class of copper proteins, the multi-copper oxidases, contains a combination of these three types of copper active sites. A reasonably firm understanding of the optical and EPR spectra of a number of copper proteins has now been achieved1,2K This article presents an overview of these electronic spectral features and their relationship to geometric and electronic structure. 

A. The Diamagnetic Copper(I) State Spectroscopic Studies and Solution Structures of Blue Copper Proteins... 

Molecular as well as spectroscopic properties of representative members of the blue copper oxidases are summarized in Tables I (62-69) and II (70-72), respectively. Data from other spectroscopic techniques used on blue oxidases, such as fluorescence, CD, or resonance Raman spectroscopy, have not been included because the implications of most of these studies are not so striking. The interested reader is referred to the existing review articles (10, 18, 19, 26). 

Additional information has been obtained from single crystal, polarized optical and ESR spectroscopic studies " on poplar plastocyanin, which have allowed a correlation of the electronic structure of the blue copper active site with its geometric structure. In summary, the three dominant absorption bands at 13 350, 16 490 and 17 870 cm were assigned to CysS Cu (d -y charge-transfer transitions. The methionine makes only a small contribution, due to the long Cu—S(Met) bond (2.9 A) and the poor overlap of the methionine sulfur orbitals with the d y orbital of copper. Histidine-Cu charge transfer contributes to the weaker absorptions at 21 390 and... 

Binding of a paramagnetic, redox-inactive [Cr(CN)6]3- anion to specific sites of a blue copper protein, amicyanin, has been used in NMR-spectroscopic studies of the protein structure in solutions.285Ab initio calculations of the ligand-field spectra of [Cr(CN)6]3 have been performed and the results compared with those for cyano complexes of the other first-row transition metals.286 The role of Cr—C—N bending vibrations in the phosphorescence spectra... 

---