An Allosteric Model of Hemoglobin

Mammalian hemoglobin binds four oxygen molecules and has different quaternary structures in the oxy and deoxy states. On the basis of this change, Monod et al. (1965), (MWC), postulated that these two states were responsible for the cooperative oxygenation of hemoglobin, suggesting that the molecule switched from the low affinity, T form, to the high affinity, R form, during the course of oxygenation. Despite the appealing nature of this model because of its ability to explain many results, its details have not been supported very directly by experimental findings. One reason is that it has been difficult to observe directly the effect upon ligand binding of changing the quaternary structure. The simplest way to obtain the deoxy quaternary structure is to deoxygenate the molecule completely, while the oxy quaternary structure is most easily obtained from the fully ligated molecule. Since it is known that increasing the number of bound ligands...