Fig. 4. Cryo-EM density map (O-state) and modelled structure of the binuclear site in CcO.

a Structural overview of the binuclear site in the O-state. The bridging peroxide species (green) is located in-between the iron (orange) and the copper (brown) atom. In close proximity to the observed bridging ligand, a second prominent density presumably molecular oxygen (purple), is located. b Measured distances (Å) for the modelled molecules at the active site. c Top view of the active site. The corresponding density map is illustrated as a white surface or mesh volumes. The illustrated map densities are filtered to equal contour levels of 1.5.