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 Å from the zinc water position, respectively, but are in close contact (2.0 and 2.6 Å, respectively) with the zinc ion.
