Monod–Wyman–Changeux model

It was proposed by Jean-Pierre Changeux in his PhD thesis, and described by Jacques Monod, Jeffries Wyman, and Jean-Pierre Changeux.

[1][2] It contrasts with the sequential model and substrate presentation.

[3] The concept of two distinct symmetric states is the central postulate of the MWC model.

The ratio of the different conformational states is determined by thermal equilibrium.

This model is defined by the following rules: In the historical model, each allosteric unit, called a protomer (generally assumed to be a subunit), can exist in two different conformational states – designated 'R' (for relaxed) or 'T' (for tense) states.

Proteins with subunits in different states are not allowed by this model.

Because of that, although the ligand may bind to the subunit when it is in either state, the binding of a ligand will increase the equilibrium in favor of the R state.

Two equations can be derived, that express the fractional occupancy of the ligand binding site (

is the allosteric constant, that is the ratio of proteins in the T and R states in the absence of ligand,

is a form of the Adair equation, but in fact it is, as one can see by multiplying out the expressions in parentheses and comparing the coefficients of powers of

[4] This model explains sigmoidal binding properties (i.e. positive cooperativity) as change in concentration of ligand over a small range will lead to a large increase in the proportion of molecules in the R state, and thus will lead to a high association of the ligand to the protein.

The MWC model proved very popular in enzymology, and pharmacology, although it has been shown inappropriate in a certain number of cases.

The best example of a successful application of the model is the regulation of hemoglobin function.

Extensions of the model have been proposed for lattices of proteins by various authors.

[8] He and Changeux[9] applied the model to signal transduction.

Changeux[10] has discussed the status of the model after 50 years.