lhh2003
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The Bohr Effect is the reduced affinity of Haemoglobin for Oxygen in a high pCO2.

Does the Haemoglobin have its Oxygen affinity reduced because it releases the Oxygen so that it can uptake the H+, meaning it prioritises binding to H+ rather than O2

OR does it have a lower oxygen affinity because it binds with the H+ just out of high probability with them being so highly concentrated, which then changes the molecules shape so it can't bind with O2 as easily ?
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lhh2003
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macpatgh-Sheldon
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Hi, sorry that you have not had an answer for so long.
Let me try to help.
The reason for the reduced affinity for O2 is that in a situation where the CO2 concentration is high, there is oc a higher rate of metabolism [at least of processes that use up O2 and give out CO2, mainly the biochemical process of respiration essential for life], which means that the requirement for O2 in this situation is greater, and greater release of oxygen from the Hb is therefore necessary.

OK that explains the reason for the [teleologically thinking] need for Hb to reduce its affinity for O2 and therefore to release it, yeah?

As for the mechanism of this reduced affinity of Hb for O2 when CO2 levels are high, there is a complex mechanism involving binding of 2,3-biphosphoglycerate [2,3-BPG], which has a strong affinity for the deoxygenated form of Hb, but not for the oxygenated form, and the binding of 2,3-BPG to deoxygenated Hb tends to stabilize this form of Hb. The binding of 2,3-BPG involves the N-terminal valines and histidine at position 143 of the beta chain of Hb.

CO2 [in common with chloride] tends to assist the binding of 2,3-BPG to deoxyhaemoglobin by strengthening its salt bridges, and this is the mechanism of the Bohr shift.

At the same time, your analysis of the need for Hb to bind H+ is not incorrect because an important function of Hb, often neglected is to bind H+ and therefore drive the breakdown of H2CO3 to release bicarbonate, hence facilitating the release of CO2 in the lungs [to be "excreted"], and the presence of H+ facilitates this process. (there is also some direct binding of CO2 to Hb, but this plays a minor role).

M
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Jpw1097
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(Original post by lhh2003)
The Bohr Effect is the reduced affinity of Haemoglobin for Oxygen in a high pCO2.

Does the Haemoglobin have its Oxygen affinity reduced because it releases the Oxygen so that it can uptake the H+, meaning it prioritises binding to H+ rather than O2

OR does it have a lower oxygen affinity because it binds with the H+ just out of high probability with them being so highly concentrated, which then changes the molecules shape so it can't bind with O2 as easily ?
The binding of H+, O2 and Hb exists as an equilibrium:
H+ + HbO2 <==> H+Hb + O2
Proton + oxyhaemoglobin <==> haemoglobinic acid + oxygen.
If you increase the H+ concentration, the equilibrium shifts to the right, forming more haemoglobinic acid and oxygen.

My understanding is the H+ ion displaces O2 causing O2 to be released, however it’s been a while since I’ve got into the nitty gritty of physiology.
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