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Competitive inhibition: Difference between revisions

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In virtually every case, competitive inhibitors bind in the same [[binding site]] (active site) as the substrate, but same-site binding is not a requirement. A competitive inhibitor could bind to an [[allosteric]] site of the free enzyme and prevent substrate binding, as long as it does not bind to the allosteric site when the substrate is bound. For example, [[strychnine]] acts as an allosteric inhibitor of the glycine receptor in the mammalian spinal cord and brain stem. Glycine is a major post-synaptic inhibitory neurotransmitter with a specific receptor site. Strychnine binds to an alternate site that reduces the affinity of the glycine receptor for glycine, resulting in convulsions due to lessened inhibition by the glycine.<ref>{{cite book |title= Pharmacology for Nurse Anesthesiology |veditors= Ouellette R, Joyce JA |year= 2011 |publisher= Jones & Bartlett Learning |isbn= 978-0-7637-8607-6 |chapter= Chapter 2. Pharmacodynamics: The Study of Drug Action | vauthors = Dick RM |url-access= registration |url= https://archive.org/details/pharmacologyforn0000ouel }}</ref>
 
In competitive inhibition, the maximum velocity (<math>V_\max</math>) of the reaction is unchanged, while the apparent affinity of the substrate to the binding site is decreased (the <math>K_d</math> dissociation constant is apparently increased). The change in <math>K_m</math> ([[Michaelis–Menten]] constant]]) is parallel to the alteration in <math>K_d</math>, as one increases the other must decrease. When a competitive inhibitor is bound to an enzyme the <math>K_m</math> increases. This means the binding affinity for the enzyme is decreased, but it can be overcome by increasing the concentration of the substrate.<ref name=":0">{{Cite book|title=Fundamentals of biochemistry : life at the molecular level| vauthors = Voet D, Voet JG, Pratt CW |isbn=9781118918401 |edition=Fifth |location=Hoboken, NJ |oclc=910538334 |date = 2016-02-29 }}</ref> Any given competitive inhibitor concentration can be overcome by increasing the substrate concentration. In that case, the substrate will reduce the availability for an inhibitor to bind, and, thus, outcompete the inhibitor in binding to the enzyme.<ref name=":0" />
[[File:Allosteric comp inhib 1.svg|350px|Competitive inhibition can also be allosteric, as long as the inhibitor and the substrate cannot bind the enzyme at the same time.|thumb]]
 
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