FIGURE 7.
Side-chain orientation of the Glu C180 conformers. Conformation “intermediate” (in solid representation, corresponding to the orientation of the ionized k-conformer) and conformation “distal” (shaded representation, corresponding to l) of Glu C180 with respect to the heme groups and the two crystallographic water molecules W11 and W33. The figure also explains the terminology intermediate and distal, since the intermediate conformation displays no preference in orientation with respect to the two hemes, whereas the distal conformation is oriented toward the distal heme group. In the case of the alternate conformers, solid representation indicates an increase of occupancy upon reduction of heme bD; shaded representation indicates a decrease. For each of the waters, the two conformers (which undergo the strongest increase and decrease, respectively, in occupancy) are depicted exemplarily.