The Linear Electric Field Effect in Stellacyanin, Azurin and in Some Simple Model Compounds

Abstract

All mononuclear Cu(I1) sites in frozen solution are non-centrosymmetric and, unless physically constrained, will have a tetrahedral distortion away from the usual square planar structure often presented for Cu(I1) complexes. Blue copper sites such as are found in azurin and stellacyanin have a greater distortion towards a tetrahedral geometry than do simple Cu(I1) complexes. The distortion is comparable to that which is observed for Cu(I1)-o-phenanthroline dichloride, a known tetrahedral complex. Blue copper sites possess an axis of asymmetry directed away from gll which could arise from a metal-sulfur interaction.

Electron spin relaxation of copper(II) complexes in glassy solution between 10 and 120K

“…2.5 mM in 2:1 toluene/chloroform. Cu(aq) 2+ [26], Cu(OH) 4 2− [17], CuEDTA [27], CuIm 4 [19] and CuMeIm 4 [19] were prepared by literature methods and characterized by visible and EPR spectroscopy. Cu(H 2 EDTA)(H 2 O) was identified by gvalues as the sole EPR-active component in a 1:1 water/glycerol solution [27].…”

“…The coordinating amino acid atoms lie approximately in the equatorial plane and the copper is just above this plane. EPR studies on PrP (23)(24)(25)(26)(27)(28) and an 15 N-labeled analogue have demonstrated that the Cu-HGGGW structure is maintained in the full prion protein octarepeat domain [20]. The S100 proteins are non-covalent homodimers.…”

“…A recent study of Cu(aq) 2+ in solution combining a full multiple-scattering analysis of the copper Kedge X-ray absorption spectrum and density functional theory indicated that it is an elongated five-coordinate square pyramid with four C-O eq bonds and a long Cu-O ax bond [24]. Linear electric field effect EPR studies by Peisach and Mims showed that both Cu(aq) 2+ and CuIm 4 in 1:1 water/glycerol glasses are D 2h -distorted [25,26]. On the basis of NMR studies [18] it was proposed that the copper(II) complex of H 2 EDTA 2− in solution at pH 7 exists as a 1:2 mixture of Cu(H 2 EDTA)(H 2 O) containing pentadentate EDTA and a coordinated water molecule and Cu(HEDTA) − containing hexadentate EDTA.…”

“…The copper(II) complexes copper(II) aqua, Cu(aq) 2+ ; copper(II) hydroxide, Cu(OH) 4 2− [17]; copper(II) ethylenediaminetetraacetate, CuEDTA [18]; copper(II) tetraimidazole, CuIm 4 [19]; copper(II) tetra-2-methylimidazole, CuMeIm 4 [19]; prion peptide sample Cu-HGGGW [20]; prion protein sample PrP (23)(24)(25)(26)(27)(28) [21]; and S100 type proteins [Cu(II)-S100A12 and Ca(II)-S100B and Cu(II)-S100B] [22] which have relatively well-defined copper centers were chosen for study.…”

Normal coordinate analysis of the copper center of azurin and the assignment of its resonance Raman spectrum.

“…Both the single copper proteins such as azurin, plastocyanin, and stellacyanin and the multi-copper proteins ascorbate oxidase, ceruloplasmin, and laccase exhibit a series ofstrong peaks in the 350-to 430-cm-' region, along with a number of weak peaks on either side of this interval. Recent advances in the structural elucidation of the copper sites of azurin and plastocyanin have helped to establish the presence of two histidine N atoms, one cysteine S atom, and, possibly, one methionine S atom as the most likely ligands in a nearly tetrahedral arrangement (6)(7)(8)(9)(10)(11)(12)(13) (14,15).…”