Sigmoid oxygen-binding curve

We can determine quantitatively the physiological significance of the sigmoid nature of the hemoglobin oxygen-binding curve, or, in other words, the biological importance of cooperativity. The equation... 

Thus, for hemoglobin (Hb) the oxygen binding curves are sigmoidal as is shown in the above figure. The fact that n exceeds the unit can be ascribed physically to the fact that attachment of O2 to one heme group... 

Hemoglobin has been a favorite protein molecule for designing and testing various models of the molecular basis of subunit interactions in multisubunit proteins. In the 1960s, two mechanisms were advanced to account for the sigmoidal nature of the oxygen binding curve for Hb A, one proposed by Monod et al. (1965) based on a... 

Oxygen binding curve is a characteristic sigmoidal ("S") shape. 

Binding of 02 to one heme group in hemoglobin increases the affinity for 02 of its other heme groups. This effect produces the sigmoidal oxygen saturation curve. 

The quaternary structure of HbA allows it to bind oxygen with positive cooperativity giving a sigmoidal oxygen dissociation curve. 

Fig. 6.2. Haemoglobin-oxygen binding curve. Note the increase in sigmoidicity as the Hill coeflicient (h) increases from I to 5.

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