Factors affects Oxygen Dissociation Curve -Organic Phosphate

The presence of organic phosphates in the red blood cells helps to explain many peculiarities of the oxygen dissociation curve. Previously the red blood corpuscle was considered to be a bag full of haemoglobin with no metabolism of its own because of the absence of a nucleus. Now we know that it has an active carbohydrate metabolism and RBC has high content of ATP and 2,3-diphosphoglycerate (DPG). 2, 3-DPG is a product of glycolysis and it binds to P chain of the globin and reduces oxygen affinity.

Experimentally it was shown that pure haemoglobin has greater oxygen affinity than whole blood (the dissociation curve for pure haemoglobin is far to the left of the curve for whole blood). If 2, 3-DPG is added to pure haemoglobin solution the oxygen affinity decreases and approaches that of whole blood. The effect of 2,3-DPG is also important in transfer of oxygen from maternal to foetal blood. Foetal haemoglobin is different from adult haemoglobin in having 2 6 chains instead of P chains. Foeta haemoglobin therefore cannot bind to 2, 3-DPG and thus has higher affinity for oxygen at a given Po2. This higher oxygen affinity in foetal blood facilitates oxygen transfer from mother to foetus.