The hemoglobin-oxygen equilibrium associated with subunit dissociation.

The effect of oxygen-linked tetramer-dimer dissociation on oxygen equilibrium of hemoglobin was investigated by measuring the equilibrium curves over a wide range of protein concentration. A Hill scheme which takes the subunit dissociation into account describes well the overall concentration dependences of the oxygen pressure and slope of the Hill plot at half saturation. Values of dissociation constant for oxyhemoglobin estimated from the equilibrium data agree with the vaues measured by other methods for phosphate-free and diphosphoglycerate-added hemoglobin. The present results indicate that oxygen equilibrium properties are only slightly influenced bysubunit dissociation in the concentration range above 60 muM (as heme) at which most equilibrium experiments have been carried out.