Allosteric theory

SCHEME 5.7 Equilibrium of the relaxed and tensed receptor conformations 

The binding of a ligand to a receptor shifts the position of the equilibrium. According to allosteric theory, agonists stabilize the relaxed conformation. The equilibrium shifts to the left, and the response increases. Inverse agonists stabilize the tensed conformation and decrease the baseline response. Antagonists bind both conformations equally and do not shift the equilibrium from its original position. 

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While occupancy theory is far and away the most widely used model for describing dose-response curves, other theories do exist. One example is allosteric theory. At the center of allosteric theory, sometimes called the two-state model, is the idea that a receptor can exist in conformations that either cause a response (relaxed state) or do not cause a response (tensed state).29 These conformations, represented by T and R, are in equilibrium (Scheme 5.7). 

Theories of interacting subunits are often referred to as allosteric theories, but the use of this word is unfortunate and should be avoided. The word allostery (Greek alios, other stereos, solid) refers to the possibility that substances (known as modifiers or effectors) can be attached at sites other than the site for the attachment of substrate. This is a completely different type of phenomenon and is of great importance in connection with the regulation of metabolic processes, but should be sharply distinguished from subunit interactions. However, in some enzymes the two effects are found together. 

One can easily understand that ten years ago namely because of the then recent success of the allosteric theory [21], well-known biochemists and biophysicists, jump-... 

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