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

The influence of the red cell concentration of 2,3-diphosphoglycerate (2,3-DPG, 0.5-26 mumoles/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 constant PCO2) 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 deltapHcell/deltapHplasma. 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 deltapHcell/deltapHplasma.