2,3 DPG stands for 2,3-diphosphoglycerate
* aka bisphosphoglycerate (BPG)
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
[HH26:p45]
2,3 DPG binds to beta chains in deoxyHb
--> Stablizes deoxyHb
--> Allows Hb to give up O2 more readily
--> Thus decreasing O2 affinity, increasing p50 value
2,3 DPG binds more weakly to HbF
--> HbF has higher O2 affinity
2,3 DPG is extruded from Hb on oxygenation
[HH26:p140; JN5:p270]
In RBC, during glycolysis,
Production of 1 ATP may be bypassed by undergoing an alternative pathway
* Rapoport-Luebering shunt [PK1:p238]
1,3-Diphosphoglycerate ----> 2, 3 DPG
* by diphosphoglycerate mutase
2,3 DPG ----> 3-phosphoglycerate
* by diphosphoglycerate phosphatase
NB:
Theoretically, 2,3-DPG level can change p50 from 15-34mmHg
However, research showed that effects in p50 due to 2,3DPG is likely to be of marginal significance in comparison with changes in arterial pO2, pH, tissue perfusion
Also see Whole blood storage
In stored blood, RBC 2,3 DPG
* Diminishes in storage
* Effectively zero after 1-2 weeks of storage
* Rate of decline depends on preservative type
After transfusion
--> RBC 2,3 DPG returns to 50% after 7 hours, and to normal levels 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 26.6mmHg)
--> 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 (18-20mmHg)
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Created | 20050305 |
Updated | 20050305 |