Figure 166.

(A) X-ray¹¹⁹⁶ and (B) calculated⁹¹⁶ structures showing the catalytic core of CcO with the formulation [(heme a₃)Fe^III- OH₂···HO–CuB^II/Tyr–O⁻]+, which has been proposed by Wikstrom and co-workers to be the relaxed oxidized species o.⁹⁰¹ However, due to the short and unreasonable O···O distance between the hydroxide and water ligand O atoms in the protein structure (A), its formulation comes into question. See text for discussion.