Allosteric enzymes are enzymes that change their conformational ensemble upon binding of an effector, which results in an apparent change in binding affinity at a different ligand binding site.
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Hemoglobin, though not an enzyme, is the canonical example of an allosteric protein molecule - and one of the earliest to have its crystal structure solved (by Max Perutz).
In biochemistry and pharmacology, 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.
Cinacalcet (INN) is a drug that acts as a calcimimetic (i.e. it mimics the action of calcium on tissues) by allosteric activation of the calcium-sensing receptor that is expressed in various human organ tissues.
Lanthanum acts at the same modulatory site on the GABA receptor as zinc- a known negative allosteric modulator.
NMDAR antagonists fall into four categories: Competitive antagonists, which bind to and block the binding site of the neurotransmitter glutamate; glycine antagonists, which bind to and block the glycine site; noncompetitive antagonists, which inhibit NMDARs by binding to allosteric sites; and uncompetitive antagonists, which block the ion channel by binding to a site within it.
The corrections have been shown to be particularly considerable for allosteric and non-allosteric enzyme-mediated reactions in intracellular compartments.