Which statement about carbonic anhydrase is true?

Which statement about carbonic anhydrase is true?

• A. Catalyzes conversion of CO2 and H2O to HHCO3 in red blood cells
• B. Causes shift to the left in oxygen dissociation curve
• C. Catalyzes formation of H2CO3 from CO2 and H2O in the tissues
• D. Inactive in renal tubular cells

Answer: (A)

Carbonic anhydrase rapidly catalyzes the hydration of carbon dioxide to carbonic acid, a crucial step for CO2 transport and acid–base balance. In red blood cells, CO2 produced by tissues diffuses into the RBCs and the enzyme speeds CO2 plus H2O converting to H2CO3, which quickly becomes bicarbonate (HCO3−) and a proton. The bicarbonate is then exchanged for chloride to travel in the plasma, delivering CO2 to the lungs for exhalation. This specific location and reaction make the statement true. It doesn’t cause a leftward shift in the oxygen dissociation curve; the curve’s position is governed by factors like pH and CO2 via the Bohr effect, which typically promotes a rightward shift in tissues and a reversal in the lungs as CO2 is removed. While the enzyme does catalyze formation of carbonic acid, the physiologically central site for CO2 hydration in transport is red blood cells, not tissues. Additionally, the kidney uses carbonic anhydrase in renal tubular cells to reclaim bicarbonate and regulate acid-base balance, so it is not inactive there.

Carbonic anhydrase rapidly catalyzes the hydration of carbon dioxide to carbonic acid, a crucial step for CO2 transport and acid–base balance. In red blood cells, CO2 produced by tissues diffuses into the RBCs and the enzyme speeds CO2 plus H2O converting to H2CO3, which quickly becomes bicarbonate (HCO3−) and a proton. The bicarbonate is then exchanged for chloride to travel in the plasma, delivering CO2 to the lungs for exhalation. This specific location and reaction make the statement true.

It doesn’t cause a leftward shift in the oxygen dissociation curve; the curve’s position is governed by factors like pH and CO2 via the Bohr effect, which typically promotes a rightward shift in tissues and a reversal in the lungs as CO2 is removed. While the enzyme does catalyze formation of carbonic acid, the physiologically central site for CO2 hydration in transport is red blood cells, not tissues. Additionally, the kidney uses carbonic anhydrase in renal tubular cells to reclaim bicarbonate and regulate acid-base balance, so it is not inactive there.