Human carbonic anhydrase II complexed with its inhibitor rhenium(I)triscarbonyl-cyclopentadienyl-carboxy-4-aminomethylbenzene-sulfonamide
[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
Enhanced receptor selectivity: Carbonic anhydrase inhibitors are relevant for both, cancer diagnosis and therapy. Combining non-radioactive Re compounds with their radioactive (99m) Tc homologs enables the use of identical molecules for therapy and imaging (theragnostic). The syntheses and in vitro evaluation of [(Cp-R)M(CO)(3) ] (CP=cyclopentadienyl, M=Re, (99m) Tc) with R being a highly potent carbonic-anhydrase-targeting vector is reported.
[(Cp-R)M(CO)(3) ] (M=Re or (99m) Tc) Arylsulfonamide, Arylsulfamide, and Arylsulfamate Conjugates for Selective Targeting of Human Carbonic Anhydrase IX.,Can D, Spingler B, Schmutz P, Mendes F, Raposinho P, Fernandes C, Carta F, Innocenti A, Santos I, Supuran CT, Alberto R Angew Chem Int Ed Engl. 2012 Feb 17. doi: 10.1002/anie.201107333. PMID:22344779
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