The Effect of pH and D-Glycerate 2,3-Bisphosphate on the O2 Equilibrium of Normal and SH(β93)-Modified Human Hemoglobin.

The present paper reports data for the effect of pH and D-glycerate 2,3-bisphosphate (D-glycerate-2,3-P₂) on the oxygen equilibrium of normal and SH(β93)-modified human hemoglobin. At sufficiently high D-glycerate- 2,3-P₂ concentrations, both oxy and deoxy forms of HbA are saturated with the organic phosphate at all pH values between 6 and 9. Furthermore the difference in the affinity for D-glycerate-2,3-P₂ between deoxy and oxy hemoglobin remains constant with pH, implying that the pK values of the Bohr effect groups in deoxy and oxyhemoglobin are not affected by the presence of D-glycerate-2,3-P₂ on the hemoglobin molecule. In the hemoglobins modified in position β93, the difference in affinity between deoxy and oxy hemoglobin for D-glycerate-2.3-P2 decreases with decrease in pH due mainly to a decrease in the affinity of the deoxy form for D-glycerate-2,3-P₂. The effect of the chemical modification appears to be primarily a change in pK of a Bohr group in deoxy hemoglobin which is especially pronounced in the presence of phosphates. [ABSTRACT FROM AUTHOR]