karbonatanhydrase

Karbonatanhydrase, commonly known as carbonic anhydrase, is a family of zinc-containing metalloenzymes that catalyze the reversible hydration of carbon dioxide to bicarbonate and a proton: CO2 + H2O ⇌ HCO3− + H+. The catalytic center features a zinc ion coordinated by histidine residues, which activates a bound water molecule to form a hydroxide ion that attacks CO2, accelerating the reaction by a large factor compared with the uncatalyzed process.

Multiple isoforms of karbonatanhydrase exist, with different cellular localizations and tissue distributions. These include cytosolic, mitochondrial, membrane-bound, and secreted forms. Some isoforms are catalytically active, while others, classified as CA-related proteins, regulate enzyme activity or serve non-enzymatic roles. The diversity of isoforms enables karbonatanhydrase to participate in a wide range of physiological contexts.

Physiologically, karbonatanhydrase plays a central role in maintaining acid–base balance, CO2 transport, and fluid production in various organs. In red blood cells, it facilitates rapid CO2 hydration, aiding its transport to the lungs. In the kidneys, it contributes to bicarbonate reabsorption and acid secretion. In secretions such as saliva and gastric juice, it supports local pH regulation and fluid formation.

Clinically, karbonatanhydrase inhibitors are used in treating conditions such as glaucoma, altitude sickness, and certain types of diuretic therapy. Common inhibitors include acetazolamide and methazolamide. The carbonic anhydrase family also includes isoforms that serve as cancer biomarkers and therapeutic targets, notably in tumors where expression of CA IX or CA XII correlates with disease progression.