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Spectroscopic studies of copper ii bound at the native copper site or substituted at the native zinc site of bovine erythrocuprein super oxide dis mutase


Journal of the American Chemical Society 104(23): 6310-6317
Spectroscopic studies of copper ii bound at the native copper site or substituted at the native zinc site of bovine erythrocuprein super oxide dis mutase
Electronic and ESR spectroscopy were used to characterize the ligand environments of CuII bound at the native Cu or Zn sites of bovine erythrocuprein (superoxide dismutase). The near-UV and visible absorption and circular dichroism spectra of the native CuII2ZnII2 and Zn-free proteins are reexamined in light of a recent study of the electronic absorption spectra of tetragonal CuII-imidazole and CuII-imidazolate model compounds. Assignments are made in the spectrum of the native CuII2ZnII2 protein for the weak but broad shoulders at 340 and 420 nm to imidazole (.pi.) to CuII and imidazolate to CuII ligand-to-metal charge transfer (LMCT) transitions, respectively. Cu(II) bound at the Zn site in the AgI2CuII2 and 4-Cu derivatives gives a broad and moderately intense band (.epsilon. .apprx. 2000 M-1 cm-1) at .apprx. 300 nm, believed to arise from carboxylate (COO-) to CuII and/or imidazole (.pi.) to CuII LMCT transitions. Ligand-field transitions at 835, 1000 and 1250 nm in the near-IR spectrum, together with a distinctly rhombic ESR signal and small hyperfine coupling constant (10.2 .times. 10-3 cm-1 at 30.degree. C), suggest that CuII bound to the Zn site in the AgI2CuII2 protein is in an environment significantly distorted from tetragonal toward a tetrahedral or distorted-pentacoordinate geometry. Some resemblances of the spectral properties of CuII in the AgI2CuII2 protein with those of modified type 3 Cu centers are also noted.

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Accession: 006461009



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