Agonist
An receptor agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance. 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.
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, 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.