Normal and Abnormal Protein Subunit Interactions in Hemoglobins

The characteristic properties of hemoglobin are due to the manner in which its individual subunits bond to one another first as an αβ dimer and then as an α2β2 tetramer. These subunit interactions also control the binding of allosteric regulatory molecules because of sites they create as they interact with one another. Some of these interactions in hemoglobin change in the transition between its tetrameric oxy (R, for “relaxed”) or deoxy (T, for “tense”) conformational states; adult human hemoglobin A (α2β2) functions as the physiological carrier of O2 between the arterial and the venous circulation in these two conformations, respectively.