The acceleration of pH volume changes in human red cells by bicarbonate and the role of carbonic anhydrase.

The red cell shrinkage rate due to bicarbonate in media of high pH (ca 9.4) has been compared with the hydroxyl shrinkage rate on a per mM basis. The shrinkage rate due to bicarbonate was only half that due to OH-/Cl- exchanges. It was therefore deduced that the Jacobs-Stewart cycle was limited by the carbonic anhydrase step and not by the rate of transport on the anion exchanger protein. To explain this and other anomalies the hypothesis is made that carbonic anhydrase has evolved as a pH-dependent catalyst with specific physiological functions in pH regulation and in other cellular mechanisms. The kinetic theory and some physiological implications of the hypothesis are discussed.