Name: competitive vs noncompetitive inhibitors
Uploaded: 2025-10-23T11:48:34.000Z
Duration: 1 min 30 s
Channel: JoVE

- Des substances chimiques spécifiquespeuvent réguler l'action des enzymes,en inhibant ou bloquant leur fonction. 
Les inhibiteurs d'enzyme se présentent sous deux formes :compétitive, et de conformation. 
Un inhibiteur compétitif est suffisamment semblableau substrat spécifique de l'enzymepour pouvoir se lier au site actifet bloquer la liaison du substrat. 
Cette action décroît, pour le substrat,le nombre d'enzymes disponibles auxquels se lier. 
En revanche, un inhibiteur de conformationne se liera pas sur le site actif, mais l'influencera,en modifiant par exemple la forme de l'enzyme,ce qui réduit grandement l'affinité du substratcensé se lier au site actifet qui empêche l'enzyme de fonctionner correctement. 
De plus, les deux types d'inhibiteur affectent différemmentla vitesse d'une réaction chimique. 
Comparée à la vitesse d'une réaction enzymatique normaleservant de contrôle,celle d'une réaction incluant un inhibiteur compétitifprend plus de temps pour atteindre la Vmax,vitesse de réaction maximale,et nécessite pour ce faire plus de substrat,car il doit y avoir plus de substratpour faire systématiquement concurrence à l'inhibiteurpour l'accès aux sites actifs. 
D'un autre côté, un inhibiteur de conformationne permet pas l'atteinte de la Vmax,car le nombre d'enzymes disponibles pour la liaisonest réduit.

Goh, Ee Teng et Marsha Y. Morgan. « Pharmacothérapie pour la dépendance à l’alcool - le pourquoi, le quoi et le comment. » Pharmacologie et thérapeutique alimentaires 45, n° 7 (2017) : 865-882. [<a href="https://doi.org/10.1111/apt.13965">Source</a>]

inhibition enzymatique

Enzyme Inhibition

Les inhibiteurs sont des molécules qui réduisent l’activité enzymatique en se liant à l’enzyme. Dans une cellule qui fonctionne normalement, les enzymes sont régulées par une variété d’inhibiteurs. Les médicaments et d’autres toxines peuvent également inhiber les enzymes. Certains inhibiteurs se lient au site actif de l’enzyme, tandis que d’autres inhibent l’activité enzymatique en se liant à d’autres sites de la structure protéique.
 
 Les inhibiteurs compétitifs occupent le site actif des enzymes, ce qui les rend incapables d’accueillir le substrat. Cependant, des concentrations suffisamment élevées de substrat peuvent surpasser l’inhibiteur ; par conséquent, les inhibiteurs compétitifs ralentissent la vitesse de réaction initiale d’une enzyme, mais n’ont pas d’impact sur la vitesse maximale de l’enzyme. Un exemple d’inhibiteur compétitif est le médicament disulfirame, employé pour traiter l’alcoolisme chronique. Lorsque de l’alcool est ingéré, il est normalement transformé en acétaldéhyde, qui est ensuite transformé en acétyl-coenzyme A par l’acétaldéhyde déshydrogénase. Le disulfirame se lie et occupe le site actif de l’acétaldéhyde déshydrogénase, ce qui rend l’enzyme incapable d’effectuer cette transformation. En conséquence, un patient prenant du disulfirame commence immédiatement à éprouver des symptômes semblables à ceux de la gueule de bois, comme le mal de tête, diminuant ainsi la consommation d’alcool.
 
 Les inhibiteurs non compétitifs se lient à des sites distincts sur l’enzyme, loin du site actif. Ceux-ci sont appelés sites allostériques et, lorsque les molécules s’y fixent, la forme du site actif est modifiée de sorte que l’enzyme a une affinité plus faible pour le substrat. Comme les inhibiteurs non compétitifs n’occupent pas le site actif, la présence de substrat supplémentaire est incapable de surmonter l’inhibition non compétitive et l’enzyme est incapable d’atteindre sa vitesse de réaction maximale.
 
 La liaison covalente entre un inhibiteur et une enzyme est généralement irréversible, comme dans le cas de certaines toxines. La plupart des inhibiteurs régulateurs normalement actifs dans la cellule interagissent avec les enzymes par le biais de faibles interactions. Ce type de liaison est réversible et utile pour la régulation des processus métaboliques. L’exploration de nouvelles molécules pour inhiber de façon compétitive et non compétitive les enzymes régulant la croissance cellulaire dans le cancer est un domaine de recherche actif.

Inhibition enzymatique

Les inhibiteurs sont des molécules qui réduisent l’activité enzymatique en se liant à l’enzyme. Dans une cellule fonctionnant normalement, les enzymes sont régulées par une variété de ...

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competitive vs noncompetitive inhibitors

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work.

Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete the inhibitor. For that reason, competitive inhibitors slow the initial reaction rate but do not change the enzyme’s maximum rate.

A clear example is disulfiram, a drug used to treat chronic alcoholism. Alcohol is normally converted to acetaldehyde and then to acetyl coenzyme A by acetaldehyde dehydrogenase. Disulfiram binds to the active site of acetaldehyde dehydrogenase and blocks this conversion. This causes hangover-like symptoms, such as headache, and helps decrease alcohol consumption.

Noncompetitive inhibitors bind at a different part of the enzyme. These binding sites are called allosteric sites. When a noncompetitive inhibitor binds, it changes the shape of the active site and lowers the enzyme’s affinity for the substrate. Extra substrate cannot overcome this effect, so the enzyme cannot reach its maximum reaction rate.

Some inhibitors form covalent bonds with enzymes. This binding is usually irreversible, as with some toxins. Most inhibitors that regulate metabolism in cells bind more weakly. That weak binding is reversible and helps control metabolic processes. Researchers also study enzyme inhibitors as possible treatments for cancers that involve cell growth.

Competitive vs Noncompetitive Inhibitors

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enzyme inhibition

Enzyme inhibitors are molecules that reduce enzyme activity by binding to enzymes. Cells use these inhibitors to help regulate normal enzyme function. Drugs and toxins can also block enzymes and change how they work. Some inhibitors bind at the active site, which is the part of the enzyme where the substrate normally fits. Competitive inhibitors do this by occupying the active site and preventing the substrate from binding. If the substrate concentration becomes high enough, it can outcompete...

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Allosteric Control of Enzyme Speed

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key terms and concepts

Compare competitive and noncompetitive enzyme inhibitors, including active-site binding, allosteric effects, disulfiram, and how inhibitors regulate cells.

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Competitive vs Noncompetitive Inhibitors

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