[aj3537]

In 1970, M. F. Perutz explained the cooperativity of oxygen binding to hemoglobin
(Hb). A great experiment by Barrick and colleagues in 1997 showed that Perutz's initial
models for cooperativity were quite accurate. Barrick used site-directed mutagenesis to
change the proximal histidine in alpha and beta chains of Hb to glycines. The mutant
hemoglobin was then mixed with imidazole, a molecule that mimics
some of the behavior of histidine.

Sketch the binding curve that you expect to see upon exposure of this mutant
Hb (in the presence of imidazole) to O2. For reference, include on the sketch the
curves for O2 binding to Hb and Mb (myoglobin).

Ok, I have the binding curve for Hb and Mb. But I'm confused about the muntant. If it mimics the behavior of histidine, then the muntant Hb mimics normal Hb. Therefore, the binding curves would be the same or slightly less. Is this correct?

[aj3537]

I forgot to post the second part of the question.

Explain your answer with respect to the theory of cooperativity of oxygen
binding and the structural changes of the heme iron center and the protein upon
binding.

I understand that binding of ligand to one site, effects the binding properities of another site in the same protein. I understand that the N is what holds the Fe and oxygen binds to the Fe.

So, if the munant mimics Histidine, then we are saying that imidazole forms a pentamer and can still hold the Fe in place which allows it to bind the neccessary ozygen?

[Yggdrasil]

There will be an important difference, however.  While the imidazole will coordinate the heme iron like the histidine, the imidazole will not be covalently connected to the alpha helix in hemoglobin.  From what you know about hemoglobin, how will this affect the properties of hemoglobin?