The unit cell of CAII crystals in space group C2 contains four molecules: I (x,y,z), II (x+1/2,y+1/2,z), III (-x,y,-z) and IV (-x+1/2,y+1/2,-z). The binding of 1 in the active site cleft of molecule I buries ∼500 Å2. Crystal contacts bury an additional 540 Å2 of the surface of 1 as follows: 270 Å2 with molecule III, and 240 Å2 and 30 Å2 with the front and back faces of molecule II, respectively. Molecule IV does not contact 1 bound to molecule I.