hemoglobin cooperativity and 2-3 BPG

[amestramgram]

Hi, is 2-3 BPG considered to change the cooperativity of hemoglobin? If so, how much does it change the cooperativity? And could you remind me what type of shape change on the O2 binding curve represents better cooperativity?
thanks for your help!

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[MrBeauregard]

When one single molecule of 2,3-bisphosphoglycerate binds a hemoglobin tetrad, it causes a shift between the alpha-beta dimers such that the taut form of hemoglobin is stabilized. This stabilization shifts the oxygen dissociation curve to the right, promoting the release of oxygen from hemoglobin in the tissues. Other things that shift the curve to the right are increased CO2, an acidotic state, high altitude, etc.

 

[Suncrusher]

Hi, is 2-3 BPG considered to change the cooperativity of hemoglobin? If so, how much does it change the cooperativity? And could you remind me what type of shape change on the O2 binding curve represents better cooperativity?
thanks for your help!

since the above post didn't address your question about cooperativity, I'd guess that it does not increase cooperativity. Cooperativity (edited to add: is a form of allosteric regulation that) makes hemoglobin more likely to bind oxygen if the other sites are already bound by oxygen. BPG is a negative allosteric regulator that makes hemoglobin bind oxygen more weakly. If the binding of BPG made hemoglobin more or less likely to bind other BPG molecules, I would call that a cooperativity mechanism; however, since it affects the binding of oxygen, I think of it merely as an allosteric regulator.

And I think it is the sigmoidal shape of the O2 binding curve that demonstrates cooperativity in general. But don't quote me on that; I've only been in med school a few months and we haven't learned that yet, so everything that I've said has been from my blurry memories of undergrad...anyway, hope this helps and that nothing I said was wrong...

 

[MrBeauregard]

Yeah, I didn't have time to address that earlier this morning because I had to get to class. Suncrusher is spot-on with the above explanation, at least compared to what I read in Lippincott's.