Extended X-ray absorption fine structure of copper in CuA-depleted, p-(hydroxymercuri)benzoate-modified, and native cytochrome c oxidase

Cytochrome c oxidase contains four redox-active metal centers: two heme irons, cytochromes a and a3, and two copper ions, CuA and CuB. Due to the paucity of spectroscopic signatures for both copper sites in cytochrome c oxidase, the ligands and structures for these sites have remained ambiguous. The specific depletion of CuA from the p-(hydroxymercuri)benzoate- (pHMB-) modified cytochrome c oxidase recently reported [Gelles, J., & Chan, S. I. (1985) Biochemistry 24, 3963-3972] is herein described. Characterization of this enzyme shows that the structures of the remaining metal centers are essentially unperturbed by the CuA modification and depletion (P. M. Li, J. Gelles, and S. I. Chan, unpublished results). Copper extended X-ray absorption fine structure (EXAFS) measurements on the CuA-depleted cytochrome c oxidase reveal coordination of three (N, O) ligands and one (S, Cl) ligand at the CuB site. Comparison of EXAFS results obtained for the CuA-depleted, pHMB-modified, and "unmodified control" enzymes has allowed the deconvolution of the EXAFS in terms of the inner coordination spheres for CuA as well as CuB. On the basis of these data, it is found that the structure for the CuA site is consistent with two (N, O) ligands and two S ligands.