title: An e.p.r. study of the non-equivalence of the copper sites of caeruloplasmin.
abstract: The two Type 1 (blue) copper-binding sites of caeruloplasmin were spectroscopically differentiated by the kinetic analysis of the e.p.r. spectra during the redox cycle. One blue copper, with a hyperfine splitting constant (A parallel) of 6.8 mT, which was rapidly reduced, was not reoxidized by oxygen, whereas it was reoxidized by H2O2. The other blue copper (A parallel = 5.8 mT), which was reduced slowly, was rapidly reoxidized by either oxygen or H2O2. A conformational change of the Type 2 copper was concomitant with the fast reduction of Type 1 copper, whereas its reduction occurred during the slow phase. This sequence of events was reversed in the reoxidation step, that is, the Type 2 copper reappeared rapidly as the species with altered conformation and reverted to the symmetry typical of the native state in the slow phase. The specific reaction of a blue-copper site with the H2O2 can tentatively be related to the established ability of caeruloplasmin to prevent 'oxidative' attack of proteins and lipids.
mesh_terms: D001665:Binding Sites; D002570:Ceruloplasmin / Q000032:analysis*; D003300:Copper / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide; D010084:Oxidation-Reduction; D011487:Protein Conformation
chemical_list: D003300:Copper; D006861:Hydrogen Peroxide; D002570:Ceruloplasmin