Binding of organic phosphates by human hemoglobin at alkaline pH-values

The hemoglobin-oxygen equilibrium binding curve was found to be sensitive to the addition of inositol hexaphosphate at pH 9.1. A solution of hemoglobin A in 0.050 $\text{M}$ sodium borate was half-saturated with oxygen at a partial pressure of 0.55mm Hg. Hemoglobin A in 0.050 $\text{M}$ sodium borate, 0.001 $\text{M}$ inositol hexaphosphate, pH 9.1 was half-saturated with oxygen at a partial pressure of 0.95mm Hg. The Hill plot was linear with a slope of 2.0 in the absence of phosphates. In the presence of inositol hexaphosphate the slope of the Hill plot increased from 1.0 to 2.36. The dependence of fractional saturation of hemoglobin with oxygen on concentration of inositol hexaphosphate was determined at partial pressures of oxygen of 0.46 and 1.07mm Hg.