Affinity of Human Hemoglobin a to 2,3—Diphosphoglycerate. Effect of Hemoglobin Concentration and of pH

The affinity of human oxy- and deoxyhemoglobin A for 2,3-diphosphoglycerate was measured in purified hemoglobin solutions at 37 °C and with near-physiological ionic composition. The affinity of both oxy- and deoxyhemoglobin for 2,3-diphosphoglycerate decreased markedly as the hemoglobin concentration increased from 0.4 to 5.5 mmol/1. The data show that, under physiological conditions, about 15 % of erythrocyte 2,3-diphosphoglycerate is bound in oxygenated cells and about 35 % in deoxygenated cells. Previous observations of the pH-dependence of the affinity of hemoglobin to 2,3-diphosphoglycerate were extended to show that the affinity of the oxygen-linked site is very similar to that found for the 2,3-diphosphoglycerate-mediated decrease in the deoxygenation rate of hemoglobin.