Question

10.39 The first-order rate constant for the dehydration of carbonic acid, H2CO3(aq) = CO2(g) + H2O(1) is about 1 x 102 s-. In view of this rather high rate constant, explain why it is necessary to have the enzyme carbonic anhydrase to enhance the rate of dehydration in the lungs.

Answer 1

Carbonic anhydrase is an enzyme which catalyses hydration and dehydration of CO₂. This enzyme is required because CO₂ hydration and HCO₃^- dehydration are often coupled to rapid processes, particularly transport processes.

For example, HCO₃^- in the blood must be dehydrated to form CO₂ for exhalation as the blood passes through the lungs. Conversely, CO₂ must be converted into HCO₃^- for the generation of the aqueous humor of the eye and other secretions. Furthermore, both CO₂ and HCO₃^- are substrates and products for a variety of enzymes, and the rapid interconversion of these species may be necessary to ensure appropriate substrate levels.

Therefore, it is necessary for the enzyme carbonic anhyrase to enhance the rate of dehydration in the lungs so that the CO2 can be expelled in proper way without disturbing the other metabolic activities.