Osmotic pressure measurements of the ligand-linked dissociation equilibrium of human oxyhemoglobin.

The tetramer/dimer equilibrium of human oxyhemoglobin has been measured by an osmometric method as a function of pH, chloride and 2,3-bisphosphoglycerate concentrations at 21 degrees C. The binding constants of chloride and 2,3-bisphosphoglycerate to the tetramer and the dimer were thus evaluated at various pH values. 2,3-Bisphosphoglycerate is bound to the dimer more strongly than to the tetramer. The dimer has a second binding site for 2,3-bisphosphoglycerate. The data for 2,3-bisphosphoglycerate binding were corroborated by direct binding measurements with the ultrafiltration method.