Structural Biochemistry/Protein function/Protein function/Binding Sites/Cooperativity

Sequential Model

The Sequential Model of the hemoglobin explains the cooperativity involved in the binding of oxygen. This model follows the concept that after binding occurs at one site in the active site, the binding affinity in the other sites around the protein will increase as well. Hence, the plot of substrate concentration versus reaction rate is of a sigmoidal shape. Because of this cooperativity, it does not follow Michaelis-Menten Kinetics. The difference between this model and concerted model is that the T states do not have to convert to R states. In this model, the ligand will change the conformation of the subunit that it is bound to and induce changes in the neighboring subunits. The Sequential model does not require the states to be in an "either T or R" ultimatum. Simply, each binding site influences nearby binding sites until all of the binding sites are in the same state. Neither the sequential model or the concerted model fully explains the nature of hemoglobin. Properties from both models appear in a real system.