Figure 4.

Views along (a) and perpendicular to (b) the threefold pore of the 60 min RcMf H54Q structure (the same arrangement is seen in the analogous wt-RcMf structure). The two Fe²⁺ hexaaqua ions are sitting on the threefold axis. The iron ions are represented as green spheres superimposed on the anomalous difference map obtained from data collected at the Fe K edge (copper wire) and the 2F _o − F _c Fourier difference map contoured at 1.2σ (blue wire). The coordinating water molecules are represented as red small spheres. Also superimposed are hydrogen bonds involving the nearby residues, which are shown as dashed lines. The open triangles and the continuous line show the position of the crystallographic threefold axis.