The separate effects of H+ and 2,3-DPG on the oxygen equilibrium curve of human blood

Addition of non-saturating amounts of 2,3-DPG (2,3-diphosphoglycerate) within the red cell (2,3-DPG/haemoglobin less than 1) initially reduces Hill's parameter, n. With increasing 2,3-DPG/haemoglobin, n increases until a maximum is reached at 2,3-DPG/haemoglobin greater than 1. Thus, 2,3-DPG influences the shape as well as the position of the whole blood oxygen equilibrium curve (OEC). The importance of this effect on the oxygen carrying capacity of the blood is considered. The effect of 2,3-DPG on the position of the OEC (p50, the PO2 at one-half maximal O2 saturation) is via its allosteric effect on haemoglobin at 2,3-DPG/haemoglobin less than 1. Above that ratio, its effect is to reduce intracellular relative to the extracellular pH.