Allosteric enzymes concerted-symmetry model

The concerted symmetry model is much more versatile than simple sequential models described by Adair or Hill. This model is endowed by the variable values of Kr, L, and c, and therefore may provide explanations for many properties of allosteric enzymes and proteins, including... 

The MWC concerted-symmetry and KNF sequential interaction models may be considered as extreme cases of the more general model shown in Fig. 19. A general model for a four-site allosteric enzyme involves the hybrid oligomers. The first and the fourth column in Fig. 19 represent the concerted-symmetry model. The diagonal represents the sequential interaction model. As shown, there are 25 different types of enzyme forms. If the potential nonequivalent complexes are included (such as, e.g., two different T3RS2), the number raises to 44 possible enzyme forms (Hammes Wu, 1971). 

Two major models for allosteric enzymes have been proposed. These are the sequential interaction model and the concerted-symmetry ... 

Two theoretical models that attempt to explain the behavior of allosteric enzymes are the concerted model and the sequential model. In the concerted (or symmetry) model, it is assumed that the enzyme exists in only two states T(aut) and R(elaxed). Substrates and activators bind more easily to the R conformation, whereas inhibitors favor the T conformation. The term concerted is applied to this model because the conformations of all the protein s protomers are believed to change simultaneously when the first effector binds. (This rapid concerted change in conformation maintains the protein s overall symmmetry.) The binding of an activator shifts the equilibrium in favor of the R form. An inhibitor shifts the equilibrium toward the T conformation. 

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