From Proteopediaproteopedia link
Joint X-ray/neutron structure of human carbonic anhydrase II at pH 7.8
[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
The neutron structure of wild-type human carbonic anhydrase II at pH 7.8 has been determined to 2.0 A resolution. Detailed analysis and comparison to the previously determined structure at pH 10.0 show important differences in the protonation of key catalytic residues in the active site as well as a rearrangement of the H-bonded water network. For the first time, a completed H-bonded network stretching from the Zn-bound solvent to the proton shuttling residue, His64, has been directly observed.
Neutron Structure of Human Carbonic Anhydrase II: A Hydrogen-Bonded Water Network "Switch" Is Observed between pH 7.8 and 10.0.,Fisher Z, Kovalevsky AY, Mustyakimov M, Silverman DN, McKenna R, Langan P Biochemistry. 2011 Nov 8;50(44):9421-3. Epub 2011 Oct 12. PMID:21988105
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.