Catalyzes the reversible hydration of CO(2) to H(2)CO(3). The main role may be to provide inorganic carbon for the bicarbonate-dependent carboxylation reactions catalyzed by pyruvate carboxylase, acetyl-CoA carboxylase and carbamoyl-phosphate synthetase. Involved in protection against oxidative damage. Encodes a substrate for the non-classical protein export pathway for proteins that lack a cleavable signal sequence. H(+) + hydrogencarbonate = CO2 + H2O Binds 1 zinc ion per subunit. kcat is 940000 sec(-1) with CO(2) as substrate. Transcription and activity down-regulated at elevated CO(2) concentrations. Present with 2330 molecules/cell in log phase SD medium. Belongs to the beta-class carbonic anhydrase family.