Why doesnt hemoglobin have any intermediate conformations be

Why doesn\'t hemoglobin have any intermediate conformations between R-state and T-state?

Solution

Answer:

X-ray crystallogarphy has determined two major conformations of hemoglobin- the T state which is stabilized in the absence of oxygen and the R state which is relatively more stable in the presence of oxygen.

The pair of identical dimers of Hemoglobin are linked by several ion pairs at the interface that stabilize it in its deoxy-state. Many of these interactions are disrupted upon binding to oxygen and new ones are formed.

There are intermediate conformations between T and R states, but the intermediate conformations have intermediate binding affinities. Also, these transition states are thermodynamically unfavourable and short lived. These states have been utilized in studying the allosteric pathways of hemoglobin. The binding of the ligand destabilizes the T state and makes it more likely to switch to the high-affinity oxygenated (oxy)-R state.