Figure 2.

The structure of the proton-conductive K-pathway leading from the surface of the protein to the binuclear center. Ser(I-299) is located at the protein surface on the proton-input side. It is at hydrogen-bonding distance from a water molecule that in turn is at hydrogen-bonding distance from Lys(I-362). The figure was prepared with visual molecular dynamics software (42) with the R. sphaeroides enzyme structure (Svensson Ek et al., unpublished results).