Fig. 4. The active site of the native CA XII structure
showing the five-coordinate zinc ion. The zinc ion is colored
cyan. Oxygen, nitrogen, and carbon atoms are red, blue, and
gray, respectively. Hydrogen bonds are shown as dashed lines
with distances labeled (Å). Average zinc-ligand distances
are as follows: Zn2+-His-94, 2.0 Å; Zn2+-His-96, 2.1
Å; Zn2+-His-119, 2.1 Å; Zn2+-OH, 2.1 Å;
Zn2+-acetate, 2.3 Å.