From Proteopediaproteopedia link
The crystal structure of the complex of hcaII with a bioreductive antitumor derivative
[CAH2_HUMAN] Defects in CA2 are the cause of osteopetrosis autosomal recessive type 3 (OPTB3) [MIM:259730]; also known as osteopetrosis with renal tubular acidosis, carbonic anhydrase II deficiency syndrome, Guibaud-Vainsel syndrome or marble brain disease. Osteopetrosis is a rare genetic disease characterized by abnormally dense bone, due to defective resorption of immature bone. The disorder occurs in two forms: a severe autosomal recessive form occurring in utero, infancy, or childhood, and a benign autosomal dominant form occurring in adolescence or adulthood. Autosomal recessive osteopetrosis is usually associated with normal or elevated amount of non-functional osteoclasts. OPTB3 is associated with renal tubular acidosis, cerebral calcification (marble brain disease) and in some cases with mental retardation.    
[CAH2_HUMAN] Essential for bone resorption and osteoclast differentiation (By similarity). Reversible hydration of carbon dioxide. Can hydrate cyanamide to urea. Involved in the regulation of fluid secretion into the anterior chamber of the eye. 
Publication Abstract from PubMed
2-Substituted-5-nitro-benzenesulfonamides incorporating a large variety of secondary/tertiary amines were explored as inhibitors of the zinc enzyme carbonic anhydrase (CA, EC 18.104.22.168), with the aim of designing bioreductive inhibitors targeting the hypoxia overexpressed, tumor-associated isozymes. The compounds were ineffective inhibitors of the cytosolic isoform I, showed a better inhibition of the physiologically relevant CA II ( K Is of 8.8-4975 nM), and strongly inhibited the tumor-associated CA IX and XII ( K Is of 5.4-653 nM). Some of these compounds showed excellent selectivity ratios for the inhibition of the tumor-associated isozymes over the cytosolic ones (in the range of 10-1395). The X-ray crystal structure of the adduct of hCA II with the lead molecule 2-chloro-5-nitro-benzenesulfonamide as well as molecular modeling studies for interaction with hCA IX afforded a better understanding of factors governing the discrimination of the two isoforms for this type of bioreductive compound targeting specifically hypoxic tumors.
Carbonic Anhydrase Inhibitors: Bioreductive Nitro-Containing Sulfonamides with Selectivity for Targeting the Tumor Associated Isoforms IX and XII.,D'Ambrosio K, Vitale RM, Dogne JM, Masereel B, Innocenti A, Scozzafava A, De Simone G, Supuran CT J Med Chem. 2008 May 16;. PMID:18481843
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.