| Agonist |
An agonist is a chemical that binds to the receptor of a cell and triggers a response from that cell. Agonists often mimic the action of a naturally occurring substance. In contrast, an antagonist is the opposite of an agonist; it binds to the receptor, but triggers no response. In pharmacology, agonists have affinity and efficacy for their receptors.
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Types of Agonist
Receptors can be activated by chemicals produced by the body (endogenous) or chemicals from outside of the body (exogenous). Therefore, an endogenous agonist for a particular receptor is a chemical produced in the body that binds to and activates that receptor.
Agonists
There are several types of agonist:
- A superagonist is an agonist that produces a greater response from the receptor than the endogenous agonist, and therefore has an efficacy of over 100%.
- A full agonist binds and activates a receptor, and has full efficacy at the receptor.
- A partial agonist binds and activates a receptor, but has only partial efficacy at the receptor.
Inverse Agonists
An inverse agonist is an agent that binds to the same receptor binding-site as an agonist for that receptor, but reverses activity of receptors. Inverse agonists exert the opposite pharmacological effect of a receptor agonist.
Allosteric Modulators
An allosteric modulator is a substance which indirectly influences (modulates) the effects of an agonist or inverse agonist at a target protein (for example a receptor). Allosteric modulators bind to a site distinct from that of the agonist binding site. Usually they induce a change within the protein structure. A positive allosteric modulator induces an amplification, while a negative modulator induces an attenuation of the effects of the ligand without triggering a functional activity on its own in the absence of the ligand.
See also
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