Figure 8.

Atomic models of the O₂reduction site structures derived from the fully reduced form, IO10, IO20, and IO80 after final structural refinements.A, the final model of the refined fully reduced form. B, the final model from IO10, obtained by final refinement under a restraint condition of Fe-O = 1.93 Å for monomer A. The distance between Cu_B atom and the distal oxygen atom of the bound O₂, averaged for the two monomers, is 2.64 Å. C and D, the final models, from IO20 and IO80, each composed of a peroxide-bound structure and a nonperoxide-bound structure, respectively, for monomer A. E, a schematic representation of the O₂ reduction site structure of the re-refined fully reduced form given in A. F–H, schematic representations of the structures including nonperoxide ligands in the final models from IO10, IO20, and IO80, respectively. The distances given in F–H are average values between the two monomers. The reliability of the Cu_B-O distance given in F, marked by an asterisk, is significantly lower than those given in G and H, because of the lower occupancy.