EVIDENCE FOR BREAKING OF THE ACTIVE-SITE DIMETAL CLUSTER IN CU,CO SUPEROXIDE-DISMUTASE UPON COPPER REDUCTION - A POLARIZED ABSORPTION-SPECTRA STUDY

The polarized absorption spectra of the cobalt chromophore in orthorho mbic crystals of bovine Cu,Co superoxide dismutase (SOD), bearing the copper ion in both the oxidized and the reduced states, are reported t ogether with the calculated isotropic spectrum. All the absorption ban ds are polarized and a spectral shift, from 598 nm to 588 nn, is obser ved in only one of them upon copper reduction. This shift, previously described in solution studies, is unequivocally assigned to the detach ment of the copper side from the imidazolate bridging copper and cobal t ions in the oxidized catalytic center. At variance with a recent X-r ay diffraction investigation on Cu(I),Zn SOD, this result indicates th at reduction of copper in Cu,Co SOD is associated to the breaking of t he dimetal cluster also in the crystalline state. (C) 1995 Academic Pr ess, Inc.