Contribution of O2 Binding Cooperativity and the Bohr Effect to Efficient Oxygen Uptake and Transport by Mammalian Hemoglobin: A New Look in the Model Protein

The slope of the oxygen equilibrium curve (OEC) of mammalian-hemoglobin (Hb) is maximized at S (oxygen saturation) value of 0.38, and the slope of the S vs. P/P50 (P is partial oxygen pressure; P50 is P at S = 1/2) plot at a P/P50 value of 1 is one-forth that of the Hill-coefficient (n). OECs of mammalian Hbs are designed to have an identical optimal P50 value for O2 delivery and the effectiveness of the Bohr shift (shift of OEC upon pH changes) at O2 loading site. This fact is favorable for uptake and delivery of maximum amount of O2 for fetal blood. To have the identical optimal P50 value for O2 delivery and for the efficiency of the Bohr shift, the relationship, PaO2/PvO2 = ((n + 1)/(n − 1))2/n, is required to hold, where PaO2 and PvO2 are P for arterial and venous bloods, respectively.