The three-dimensional structure of human carbonic anhydrase II complexed with
azide and with bromide was investigated crystallographically. Both of these
non-protonated inhibitors replace the zinc and the 'deep' water, two
catalytically important water molecules in the active site of the molecule. Both
the azide and the bromide ions bind in a distorted tetrahedral manner 0.4 and
1.1 A from the zinc water position, respectively, but are in close contact (2.0
and 2.6 A, respectively) with the zinc ion.