The Effect of pH and d‐Glycerate 2,3‐Bisphosphate on the O2 Equilibrium of Norma1 and SH(β93)‐Modified Human Hemoglobin

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Abstract
The effect of pH and D-glycerate-2,3-bisphosphate (D-glycerate-2,3-P2) on the oxygen equilibrium of normal and SH(.beta.93)-modified human Hb was studied. 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-P3 between deoxy-Hb and HbO2 remains constant with pH, implying that the pK values of the Bohr effect groups in deoxy-Hb and are not affected by the presence of D-glycerate-2,3-P2 on the Hb molecule. In the Hb modified in position .beta.93, the difference in affinity between deoxy-Hb and HbO2 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-Hb which is especially pronounced in the presence of phosphates.