Regulation of hemoglobin affinity for oxygen by carbonic anhydrase.

Abstract We studied the effect on hemoglobin (Hb)–oxygen affinity induced by changes in carbonic anhydrase (CA) activity. Oxygen partial pressure at the 50% saturation of Hb (P 50 ) in human blood was measured as CA activity was inhibited to varying degrees with acetazolamide (AZ; 100 and 200 μg/mL). Transient but significant change in P 50 was observed when AZ was administered and the CO 2 concentration was changed from 10% to 5%. Finally, the differences induced with AZ were attenuated when the blood sample was subjected to 4 hours of tonometry. The findings in this study could be accounted for by reduced velocity of pH changes caused by the inhibition of CA by AZ. We conclude that CA can change Hb's affinity for oxygen by controlling the movement of CO 2 gas between air and liquid compartments.