Hemoglobin cooperativity, molecular mechanism

The structural and functional properties of human hemoglobin (Hb) have been the subject of study for decades, stimulated by the intriguing characteristic of positive cooperativity. How do the four subunits that compose the Hb tetramer communicate with one another The answer to this question has been sought primarily through the comparison of deoxy with oxy Hb. However, to understand the molecular mechanism of a chemical reaction, it is necessary to characterize the intermediate(s) of the process, and the reaction of Hb with O2 is no exception. 

The interest in the structure-function relationship in hemoglobin has been primarily focused on the molecular mechanism of the cooperative oxygen binding. The main relevant structural information related to this problem was the differences observed between the oxy and deoxy structures of hemoglobin. However, little is known about the structure of the intermediately oxygenated hemoglobin molecules. Several models have therefore been proposed in order to... 

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