Fig. 3.
(Fo-Fc) difference electron density map of the 15-s data calculated at 2.1-Å resolution. (A)Electron density cages for the electron density between and Fea3 and CuB, and for 3 water molecules depicted at the 5.2σ level in a stick model around the O2 reduction site. Carbon, nitrogen, and oxygen atoms are colored in yellow, blue, and red, respectively. (B) (Fo-Fc) difference maps for the 15-s dataset obtained under 3 different constraints on the O
O distance. Cages are depicted at the 3.8σ level. Heme a3 is depicted by a ball-and-stick model. Carbon, nitrogen, and oxygen atoms are yellow, blue, and red, respectively. The peroxide anion is illustrated by a stick model. Fea3 and CuB are represented in brown and green. The map of the 1.6-Å constraint (pink) has residual density peaks at both ends of the OO bond, whereas the map of the 1.8-Å constraint (green) has a large residual density at the middle of the OO bond. The cages for the 1.7-Å constraint (blue) have the smallest residual density.