Explain why BPG, even at higher concentration, does not affect O2 binding to Hb in the...

Explain why BPG, even at higher concentration, does not affect O2 binding to Hb in the lungs?

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Expert Solution

Human blood contain a compound called 2,3-BPG (Bisphosphoglycerate). This compound has allosteric effect. There are so many allosteric regulators for haemoglobin. BPG is one of them.

This BPG molecule binds to the central part of the deoxyhaemoglobin version of haemoglobin and stabilizes it. This state is known as T-state. If oxygen is bound to the haemoglobin, the T-state loses its strain and relaxes. That is called R-state. If T-state stability increased, the affinity towards oxygen will decrease. So BPG makes haemoglobin less likely to bind oxygen in an attempt to release the strain. In T- state, haemoglobin is very unstable. So BPG is needed to stabilize it. Because BPG decreases haemoglobin’s affinity for oxygen, it is an allosteric inhibitor of haemoglobin. Without BPG, haemoglobin would be an extremely inefficient transporter of oxygen from the lungs to the tissues, releasing only about 8% of its oxygen content. However, in the presence of 2,3-BPG, more oxygen-binding sites in the haemoglobin tetramer must be filled in order to transition from the T to the R state. Higher concentrations of oxygen must be reached in order for haemoglobin to transition from the lower-affinity T-state to the higher-affinity R state. So it will not affect the oxygen binding in lungs.

queen_honey_blossom answered 1 year ago

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