Figure 5 - full size

 

Figure 5.
Fig. 5. Redox-controlled proton collection and supply by His-503. Only one of the water arrays connecting W207 and W4 and two other possible hydrogen-bonding groups to W207 is shown for the sake of simplicity. The red and blue structures represent the oxidized and reduced (or electron-released and electron-accepted) states of the redox site (or sites) controlling the conformation of the imidazole of His-503. The structures before the oxidation state change are the stable oxidized and reduced states. The circles with arrowheads indicate the rotation of the imidazole group during the transition.