Binding oxygen to hemoglobin

Thermodynamically it would be expected that a ligand may not have identical affinity for both receptor conformations. This was an assumption in early formulations of conformational selection. For example, differential affinity for protein conformations was proposed for oxygen binding to hemoglobin [17] and for choline derivatives and nicotinic receptors [18]. Furthermore, assume that these conformations exist in an equilibrium defined by an allosteric constant L (defined as [Ra]/[R-i]) and that a ligand [A] has affinity for both conformations defined by equilibrium association constants Ka and aKa, respectively, for the inactive and active states ... 

Hemoglobin also binds H+ and C02, resulting in the formation of ion pairs that stabilize the T state and lessen the protein s affinity for 02 (the Bohr effect). Oxygen binding to hemoglobin is also modulated by 2,3-bisphosphoglycerate, which binds to and stabilizes the T state. 

Ligand A molecule that binds to another molecule. For example, when oxygen binds to hemoglobin, oxygen is a ligand. 

Figure 3. Illustration of how the osmotic stress method is used to measure the volume associated with the process of oxygen binding to hemoglobin.

The major agents that affect oxygen binding to hemoglobin are shown in Figure 44.11. 

---