2,3-bisphosphoglycerate(2,3-BPG) is a three carbon isomer of the metabolic intermediate 1,3-bisphosphoglycerate. It is present in human red blood cells in the same molar ratio as haemoglobin. Its function was discovered in 1967 by Reinhold Benesch and Ruth Benesch.

It binds deoxyhaemoglobin and thus acts to stabilises the low oxygen affinity state (Tense state) of the oxygen carrier. 2,3-bisphosphoglycerate fits neatly into the cavity of the deoxy conformation exploiting the molecular symmetry and forming salt bridges with lysine and histidine residues in the 4 subunits of haemoglobin. The Relaxed state, with oxygen bound to the haem group, has a different conformation and does not allow this interaction.

2,3-BPG is essential in unloading oxygen under physiological conditions. Levels of 2,3-BPG are higher in those acclimatised to high altitudes. Fetal haemoglobin has a low binding affinity for 2,3-BPG, hence overall affinity of haemoglobin F for oxygen is higher.

Further reading

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Berg, J.M., Tymockzko, J.L. and Stryer L. Biochemistry (5th ed) W.H. Freeman and Co, New York, 1995 ISBN 0716746840