Abstract

Carbonic anhydrase, a metalloenzyme which catalyses the reversible interconversion of HCO₃^? and CO₂, is a major protein component of higher plant tissues. It is now shown that DNA sequence and encoded proteins for the different ?, ?, ?, ?, ?, and ? forms of carbonic anhydrases are present in living organisms. While there are no sequence homologies between the different type of carbonic anhydrases, all the ?, ?, and ? carbonic anhydrase gene family enzymes in higher plants catalyze the same chemical reaction. Its specific function is generally assumed to convert CO₂ to HCO₃^? for the phosphoenolpyruvate carboxylase reaction and convert HCO₃^? to CO₂ for the ribulose-1,5-bisphosphate carboxylase reaction in photosynthesis. Moreover, carbonic anhydrase activity in guard cells is required for CO₂-mediated stomatal regulation and carbonic anhydrases may provide an approach for plant alternatively protection against stress conditions. Recent studies on carbonic anhydrases described in this manuscript include the characterization and gene family of carbonic anhydrases, physiological function of higher plant CAs, and gene engineerings about higher plant CAs.

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