Dual effect of 2,3-diphosphoglycerate on the Bohr effects of human blood

Abstract

The influence of the red cell concentration of 2,3-diphosphoglycerate (2,3-DPG, 0.5–26 μmoles/g erythrocytes) on the “CO₂-Bohr effect” (pH varied by CO₂ at constant base excess) and the “fixed acid-Bohr effect” (pH varied by fixed acid or base at constantP _CO2) was studied in human blood at plasma pH values ranging between pH 7.2 and pH 7.6. Elevation of red cell 2,3-DPG concentration leads to a numerical decrease of the “CO₂-Bohr coefficient” referring to plasma pH. The “fixed acid-Bohr coefficients” are numerically smaller than the corresponding “CO₂-Bohr coefficients” and exhibit a maximum at normal red cell 2,3-DPG concentrations. The Bohr coefficients referring to red cell pH are distinctly higher than those referring to plasma pH, especially at high 2,3-DPG levels. This is due on the one hand to the physico-chemical properties of the intact red cell membrane, and on the other hand to a 2,3-DPG-induced decrease in the ratio ΔpH_cell/ΔpH_plasma. From the results it is concluded that 2,3-DPG exerts a dual effect on the Bohr coefficients of whole blood which is mediated 1. by the direct effect of 2,3-DPG on the allosteric properties of hemoglobin (as reflected by changes of the Bohr coefficients referring to red cell pH), and 2. by the effect of 2,3-DPG on ΔpH_cell/ΔpH_plasma.