Carbonic anhydrase II and Carbonic anhydrase III (CA II, CA III)

Carbonic anhydrase II (CA II) and carbonic anhydrase III (CA III) are two major members of the carbonic anhydrase enzyme family in mammals. They are zinc-dependent metalloenzymes that catalyze the reversible hydration of carbon dioxide (\(\mathrm{CO_2}\)) to bicarbonate (\(\mathrm{HCO_3^-}\)) and protons (\(\mathrm{H^+}\)). CA II is exceptionally efficient, with turnover rates up to \(10^6\) molecules of CO₂ per second, and is widely expressed in red blood cells, renal tubules, and other tissues. CA III is present mainly in skeletal muscle and adipose tissue, with lower catalytic efficiency. The enzymes play critical roles in maintaining acid-base homeostasis, respiratory gas transport, and fluid secretion. Both are therapeutic targets for drugs like acetazolamide (used in glaucoma, altitude sickness, epilepsy) and experimental cancer therapies. The enzyme's active site includes a tetrahedrally coordinated zinc ion bound by three histidines and water, surrounded by specialized residues crucial for catalysis and inhibitor binding.

Other names

CA IIhCA IIcarbonate hydro-lyase IICA IIIhCA IIIcarbonate hydro-lyase III

Competitive inhibition of the active site, especially the Zn²⁺ center. Disruption of catalytic hydration/dehydration of CO₂, affecting acid-base balance and fluid secretion. Reversible binding to the active-site zinc.