Fig. 1.
(A and B) The BNC of CcO from Bos taurus (PDB ID code 1V54). The T-shaped three-coordinate structure (A) and near planarity (B) of the CuB center are shown. The copper, its histidine ligands, heme, and cross-linked tyrosine are displayed in orange, blue, gray, and green, respectively. (C) The proposed catalytic cycle is drawn clockwise. The oxidation states of Fe, CuB, and the cross-linked tyrosine in the BNC are shown, along with protonation states of the cross-linked tyrosine and metal ligands. The name of each state is shown in the upper right corner of each yellow rectangle. Blue arrows show proton pumping, whereas electrons and protons consumed at the BNC are shown in red and black, respectively. O2 binds to the BNC in the R→A transition.