Carbon dioxide binding site. Crystals of carbonic anhydrase were exposed to carbon dioxide gas at high pressure and low temperature, and x-ray diffraction data were collected. The electron density for carbon dioxide, clearly visible adjacent to the zinc and its bound water, reveals the carbon dioxide binding site.

[Information from J. F. Domsic, et al., J. Biol. Chem. 283:30766–30771, 2008.]