Carbonic anhydrase catalyses the formation of

RBCs contain a very high concentration of the enzyme, carbonic anhydrase and minute quantities of the same is present in the plasma too. In the systemic capillaries this enzyme facilitates the formation of ${\mathrm{H}}_2{\mathrm{CO}}_3^{-}$ from ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$. In the pulmonary capillaries the same enzyme facilitates the dissociation of ${\mathrm{H}}_2{\mathrm{CO}}_3^{-}$ into ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$.