AN EXTENDED-X-RAY-ABSORPTION-FINE-STRUCTURE STUDY OF BOVINE ERYTHROCYTE SUPEROXIDE-DISMUTASE IN AQUEOUS-SOLUTION - DIRECT EVIDENCE FOR 3-CO-ORDINATE CU(I) IN REDUCED ENZYME

Cu and Zn K-edge e.x.a.f.s. (extended X-ray-absorption fine structures) were measured for the metal sites of oxidized and reduced bovine superoxide dismutase in aqueous solution. Detailed analysis of the spectra indicated that the Cu site of the enzyme changes on reduction and is most probably co-ordinated to 3 imidazole groups at a shorter distance Cu-N(.alpha.) = 0.194 nm (1.94 .ANG.) in the reduced form compared with a co-ordination of 4 imidazole groups at 0.199 nm (1.99 .ANG.) and an O atom from solvent water at 0.224 nm (2.24 .ANG.) in the oxidized form. Examination of the edge, near-edge structure and e.x.a.f.s. of the Zn sites indicates that the stereochemical changes at Cu that accompany reduction introduce minimal perturbation on the stereochemistry at Zn.