Carbonic anhydrase isoform (CA)

Carbonic anhydrase isoforms are a family of zinc-containing metalloenzymes that catalyze the reversible conversion of carbon dioxide and water to bicarbonate and protons, a fundamental reaction for pH, CO2, and bicarbonate homeostasis in virtually all tissues[1][2][3][6]. In humans, there are at least 15–16 distinct isoforms (e.g., CA I, CA II, CA IX, etc.), each with specific tissue distribution, localization (cytosolic, membrane-bound, mitochondrial, secreted), and physiological functions[2][3][8]. Isoform selectivity is important for therapeutic targeting: for example, CA IX and CA XII are transmembrane glycoproteins markedly overexpressed in certain cancers and key to tumor acidification, whereas CA II is the major cytosolic isoform in red blood cells and kidneys[2][7]. Clinically, CA inhibitors (such as acetazolamide and dorzolamide) are widely used for treating glaucoma, epilepsy, edema, and have investigational utility in cancer therapy, especially for tumors expressing CA IX/XII. Selective inhibition remains a challenge due to high conservation across isoforms, and off-target effects limit some clinical uses[1][5][8]. Besides therapeutic applications, CA isoforms also serve as biomarkers, for example CA IX as an indicator of tumor hypoxia and prognosis in renal cell carcinoma[7]. The enzymes are classified as hydrolases (EC 4.2.1.1), with the α-class being the only one found in humans; other classes exist in bacteria, plants, and algae[2][3][8].

Other names

CACA isozymeCA isoformcarbonic anhydraseα-carbonic anhydrase (when specifically referring to the human or vertebrate class)CA I/II/IX/XII etc. (for specific isoforms)

Inhibition of CA catalytic activity (blocking reversible hydration of CO2/bicarbonate) Inhibition of pH regulation, leading to reduced aqueous humor formation (antiglaucoma) Inhibition of extracellular acidification in tumors (anticancer, via CA IX/XII) Reduction of abnormal neuronal excitability (antiepileptic, via CA VII inhibition) Enhancement of bicarbonate excretion (diuretic/antiedema effect)