What is 2,3, DPG? How is it produced in the red blood cell and how does it interact with haemoglobin? What is its relevance in altitude exposure, stored blood and anaemia. (95A1) (1991)
Reference: Nunn p.269
Binds to beta-chain of one tetramer of deoxyhaemoglobin, causes conformational change that reduces O2 affinity (displacing dissociation curve to the right).
=> Increased levels of 2,3 DPG
=> reduced the affinity of haemoglobin
=> Right shift of ODC
1,3-Diphosphoglycerate -> 2, 3 DPG
=> by diphosphoglycerate mutase
2,3 DPG -> 3-phosphoglycerate
=> by diphosphoglycerate phosphatase
At high pH, 2,3 DPG is increased because activities of DPG mutase is enhanced and DPG phosphatase is diminished.
Red cell 2,3 DPG in stored blood diminishes in storage and is effectively zero after 1-2 weeks
=> rate of decline depends on types of preservative used
After transfusion, red cell 2,3 DPG returns to 50% after 7 hours, and to normal level after 48 hours.
In theory, decreased 2,3 DPG can impair tissue oxygenation.
In reality, changes in P50 usually is less than 0.5kPa (or 3.8mmHg), and effect is quite minimal.
Anaemia results in a raised 2,3 DPG level.
=> Increased P50 to 30mmHg (from 27mmHg)
=> improve oxygen unloading in the tissues (by maintaining pressure gradient).
Altitude causes an increased red cell concentration of 2,3 DPG.
But, progressive respiratory alkalosis due to altitude will have an opposite effect and much more pronounced.
Thus, ODC still shift to left despite increased 2,3 DPG.
Foetal haemoglobin has 2 alpha chains and 2 gamma chains and no beta chains.
=> less sensitive to effect of 2,3 DPG
=> P50 lower
None.
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| Updated | 20050305 |