Why is carbonic anhydrase essential to Escherichia coli?
The can (previously yadF) gene of Escherichia coli encodes a beta-class carbonic anhydrase (CA), an enzyme which interconverts CO(2) and bicarbonate. Various essential metabolic processes require either CO(2) or bicarbonate and, although carbon dioxide and bicarbonate spontaneously equilibrate in solution, the low concentration of CO(2) in air and its rapid diffusion from the cell mean that insufficient bicarbonate is spontaneously made in vivo to meet metabolic and biosynthetic needs. We calculate that demand for bicarbonate is 10(3)- to 10(4)-fold greater than would be provided by uncatalyzed intracellular hydration and that enzymatic conversion of CO(2) to bicarbonate is therefore necessary for growth. We find that can expression is ordinarily required for growth in air. It is dispensable if the atmospheric partial pressure of CO(2) is high or during anaerobic growth in a closed vessel at low pH, where copious CO(2) is generated endogenously. CynT, the single E. coli Can paralog, ca
