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Complexation of type 2 copper by cytochrome c oxidase: probing of metal-specific binding sites by electron

H Yuan¹, W E Antholine, P M Kroneck

¹Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226-0509, USA.

Journal of Inorganic Biochemistry

|October 2, 1998

Abstract:

Cytochrome c oxidase, CcO, contains at least four, probably five type 2 copper binding sites per monomer in addition to the mixed valence [CuA(1.5+)CuA(1.5+)], S = 1/2 center and the EPR-silent CuB. Electron paramagnetic resonance (EPR) parameters for these site are g parallel = 2.22 and A parallel = 195 G. Nitrogen superhyperfine structure is observed in the g perpendicular region, with A perpendicular N of around 15 G. The EPR parameters for Cu(2+) bound to a synthetic peptide, AHGSVVKSEDYALPS, are similar to the parameters for the type 2 sites in CcO. The lines in the EPR spectrum of the type 2 site in the synthetic peptide are better resolved at low microwave frequency (3.4 GHz). Resolved lines in the expansion of the MI = -1/2 line in the g parallel region of the low frequency spectrum are attributed to superhyperfine structure from three almost equivalent nitrogen donor atoms bound to Cu(2+) in a square planar configuration. The MI = -1/2 line in the g parallel region for excess Cu(2+) bound to CcO is not as well resolved as for the synthetic peptide, presumably because the four or five binding sites per monomer are similar, but not exactly equivalent. These binding sites are proposed to be at the N-terminus of subunits of CcO, for example, at subunit IV where the sequence is AHGS-. Nitrogen donor atoms from the alpha-amino group of the amino terminal residue, the imidazole group of histidine, and a peptide nitrogen are predicted to comprise the binding site.

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