Biomedical Engineering: Bridging Medicine and Technology 1st Edition by Veronique Tran,Mark Saltzman

Exercise 10

Carbonic anhydrase is an enzyme important to the management of CO2 (car- bon dioxide). About 11% of the blood's CO2 is transported by hemoglobin. Most of the CO2 that enters the erythrocytes (red blood cells) dissolves in the cytoplasm (cellular fluid). It then combines with water molecules to form carbonic acid, which immediately disassociates into hydrogen ions and bicarbonate. This reaction is sped up about 250 times by the enzyme car- bonic anhydrase (Km = 1000 µM) that is located in the erythrocytes. Most of the CO2 is converted into bicarbonate as soon as it enters red blood cells, thus keeping the CO2 level in the cell lower than that of the interstitial fluid. This lowering of intracellular level is important as the concentration gradient between the interstitial fluid and the surrounding tissue increases the diffu- sion efficiency of CO2, allowing it to be removed quickly from tissues. In a reaction vessel (which simulates body conditions) it was found that, in the presence of carbonic anhydrase, 5% of the initial 0.840993 M of CO2 was converted after 2 seconds. How much CO2 will be converted after 10, 30, and 60 seconds? State any simplifying assumptions.