Reversible hydration of carbon dioxide. H(+) + hydrogencarbonate = CO2 + H2O Inhibited by acetazolamide. Expressed at lower levels in adipose tissue from animals that were either genetically obese or had experimentally induced obesity. S-thiolated both by thiol-disulfide exchange with glutathione disulfide and by oxyradical-initiated S-thiolation with reduced glutathione. S-glutathionylated in hepatocytes under oxidative stress. Belongs to the alpha-carbonic anhydrase family.