Figure 4.

Differences in the occupancy of the quinone reduction sites (Q_i sites) of the homodimeric QCR. The Q_i site of (A) monomer A and (B) monomer B, the latter has CYC bound, is shown with part of the quinone-ligating sphere including Ser-206, Met-221, and propionate A (propA) of heme b_H. The electron-density map after final refinement is shown in blue (2F_obs − F_calc; contoured at 1σ) and in green (F_obs − F_calc; contoured at 3σ). Protein and cofactors are shown as stick drawings with atoms displayed in standard colors. The figure was prepared by using the program o (22).