Mechanism and kinetics of the Haldane effect in human erythrocytes

The equilibrium and kinetic characteristics of the Haldane effect were studied using a continuous flow reaction apparatus. The relative contributions of carbamate and bicarbonate to the total Haldane effect were evaluated by inhibiting carbonic anhydrase with acetazolamide. The Haldane effect was minimally influenced by change in 2,3 diphosphoglycerate (2,3 DPG) concentration, but the relative contribution of oxylabile carbamate decreased markedly as 2,3 DPG increased. With normal concentration of 2,3 DPG the Haldane effect was relatively constant at 0.25-0.30 mmole CO₂ released/mmole O₂ bound above pH 7.3, but decreased sharply at lower pH. Mobilization of oxylabile carbamate followed an exponential time course with a mean rate constant of 6.4 sec^-1. The oxylabile bicarbonate reaction appeared to be rate limited by the dehydration of carbonic acid and the transmembrane exchange of chloride and bicarbonate. The dehydration reaction was catalyzed by carbonic anhydrase by a factor of 16,000. The apparent rate constant for the chloride bicarbonate exchange averaged 4.3 sec^-1 and was inversely proportional to pH.