From Proteopediaproteopedia link
Human carbonic anhydrase II in complex with p-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)benzenesulfonamide
[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
We have determined the protein X-ray crystal structures of four organometallic inhibitors in complex with their target enzyme carbonic anhydrase II. The barrel-shaped hydrophobic ferrocene and ruthenocene moieties have provided a structure-based avenue to better occupy the hydrophobic binding patch within the enzyme active site.
Protein crystal structures with ferrocene and ruthenocene-based enzyme inhibitors.,Salmon AJ, Williams ML, Hofmann A, Poulsen SA Chem Commun (Camb). 2012 Feb 25;48(17):2328-30. Epub 2012 Jan 18. PMID:22258283
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.