Theoretical Models for Allosteric Effect

Two theoretical models for allosteric effects have been proposed to explain the mechanism for ligand-protein cooperative interactions the concerted (or symmetry) model of Monod, Wyman, and Changeux and the sequentially induced-fit model of Koshland. The nomenclature associated with allosterism and cooperativity originated from the concerted model. Both models assume that 

Each subunit of an oligomeric protein exists in two forms, T and R, which bind the ligand with low and high affinity, respectively and 

The T R transformations involve noncovalent bonds and result in changes in the quaternary structure of the enzyme. 

Negative modulator preferentially binds to the T form and maintains the allosteric protein in the TT conformation. 

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