Carbonic anhydrase II and Carbonic anhydrase IV (CA II and CA IV)

Carbonic anhydrases are a family of zinc-containing metalloenzymes that catalyze the reversible hydration of carbon dioxide into bicarbonate and protons—a reaction fundamental for maintaining acid-base balance across tissues. Carbonic anhydrase II is a highly active cytosolic isoenzyme found abundantly in red blood cells, kidneys, osteoclasts, platelets, gastric mucosa, among others. It plays critical roles in pH regulation throughout various organs; its dysfunction is linked with diseases such as osteopetrosis and renal tubular acidosis due to impaired bone resorption or renal bicarbonate reabsorption respectively.[5][9] Carbonic anhydrase IV is a membrane-bound isoenzyme anchored via glycosylphosphatidylinositol linkage on cell surfaces—particularly important on vascular endothelium—and also exhibits high catalytic efficiency similar to CA II.[1][2] Both enzymes are therapeutic targets for sulfonamide inhibitors used mainly in glaucoma management by reducing intraocular pressure through decreased aqueous humor formation.[2][8] Their broad physiological roles extend from respiration/CO₂ transport to ion exchange processes vital for homeostasis across multiple organ systems.[3][4]

Other names

CA2 (for Carbonic anhydrase II)CA4 (for Carbonic anhydrase IV)EC 4.2.1.1 (Enzyme Commission number for carbonic anhydrases)Human carbonic anhydrase IIHuman carbonic anhydrase IV

Drugs such as acetazolamide or brinzolamide inhibit the enzymatic activity by binding to the zinc ion at the active site, blocking conversion between CO₂ and bicarbonate.[8] This reduces aqueous humor production in the eye or alters acid-base balance systemically.