Carbonic anhydrase is a zinc metalloenzyme found in animals, plants, algae, and prokaryotes. This enzyme catalyzes the hydration reaction of carbon dioxide (CO2) into bicarbonate (HCO3−) and protons (H+), playing a crucial role in different physiological processes. Five carbonic anhydrase families, referred to as α, β, γ, δ, and ζ have been identified in animals and plants. The structure of the α-carbonic anhydrase family is characterized by three histidine residues that bind the zinc cofactor, and a proton shuttling residue at the entrance of the active site is responsible for converting a zinc-bound water molecule to a hydroxide ion.In animals, carbonic anhydrase is present in many different tissues and is involved in numerous physiological processes, including osmoregulation, ion transport, acid–base regulation, respiration, and calcification. 
In algae and plants, this enzyme plays an important role in photosynthesis.Aquatic organisms have high concentrations of carbonic anhydrase in this tissue, where this enzyme plays an essential role in maintaining constant levels of osmolytes, such as Na+ and Cl−, that are important for cell function.The mammalian lung has carbonic anhydrase associated with the endothelial membrane that is exposed to plasma, and the kidney tubule also has carbonic anhydrase present on the luminal brush borders. Carbonic anhydrase is also important for mitochondrial metabolism as the HCO3− resulting from this enzyme activity provides an intra mitochondrial counter-anion facilitating Ca2+ accumulation in the mitochondrial matrix in the form of CaCO3. Carbonic anhydrase plays an important role in biological calcification, a fundamental process performed by a great number of marine invertebrates. This process occurs at the interface between organic and mineral tissues, with the formation of an organic matrix that acts as the deposition center of CaCO3 crystals, termed as the calcification site.

References

1.Yuri Dornelles Zebral,et al. Int J Mol Sci. 2019 Jun; 20(12): 3092.