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Spectroscopic studies of ceruloplasmin electronic structures of the copper sites






Journal of the American Chemical Society 101(17): 5046-5053

Spectroscopic studies of ceruloplasmin electronic structures of the copper sites

Low temperature absorption and room temperature circular dichroism [CD] and magnetic circular dichroism [MCD] spectra were measured for the blue copper oxidase ceruloplasmin. Azide- and thiocyanate-bound ceruloplasmins were examined by the 2 latter techniques. Low energy ligand field transitions were located in the native (6100, 10,000, and 11,500 cm-1) and azide-bound (8940 and 12,000 cm-1) proteins that were of similar energy to those previously attributed to a flattened tetrahedral type 1 (blue) copper in other blue copper proteins. The MCD spectrum, featuring a single negative band at 14,600 cm-1, was similar to those of the other blue copper proteins. Both blue copper sites in ceruloplasmin were evidently structured in the same manner as the CuN2SS* (N = His, S = Cys, S* = Met) unit in azurin and plastocyanin. Examination of the ligand field spectra showed conclusively that structural changes in both type 1 coppers occur on anion binding. Analysis of the d-d spectrum of azide-bound ceruloplasmin required a larger distortion away from a tetrahedral structure than was indicated for native type 1 copper. An ascorbate-modified (type 1 depleted) derivative of ceruloplasmin was characterized; its absorption (16,500 cm-1), CD (13,700, 17,000, 19,800, 22,200, 25,300 and 32,000 cm-1) and EPR (g.perp. = 2.06, g.dblvert. = 2.26; A.dblvert. = 170, AN = 14 G) spectra were measured. The band positions observed in absorption and CD ruled out tetrahedral or near-tetrahedral geometries for the type 2 and type 3 coppers. A tetragonal structure for type 2 copper with 4 N-donor ligands was suggested by the 9-line superhyperfine splitting pattern seen in the g.perp. region of ascorbate-modified ceruloplasmin.

Accession: 006461003

DOI: 10.1021/ja00511a040

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