The active site of human carbonic anhydrase

In the drawing, the light gray ligand to the Zn+2 indicates the probable fifth Zn+2 coordination site (not shown in 3D window). In the 3D window on the left, a Zn2+ ion and a water molecule are represented by magenta and red spheres, respectively. Arrow points toward the opening of the active site cavity. Spacefill representation is used to illustrate both solvent and reactant accessability to the active site.