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

هناك أنواع محددة من المواد الكيميائية يمكنها تنظيم عمل الإنزيمات عن طريق تثبيط وظيفتهم أو منعها. وهناك نوعان مختلفان من مثبطات الإنزيمات،مثبطات تنافسية ومثبطات لا تنافسية. المثبط التنافسي يشبه إلى حد كبير الركيزة المخصصة للإنزيم ويمكنه الارتباط بالموقع النشط،ومنع الركيزة من الارتباط بالإنزيم.ويؤدي هذا بالأساس إلى تقليل عدد الإنزيمات المتاحة للارتباط مع الركيزة. وعلى العكس،المثبطات اللا تنافسية سترتبط بعيداًولكن مازال يمكنها التأثير على الموقع النشط،عن طريق تغيير شكل الإنزيم،على سبيل المثال،ويُقلل بشكل كبير الانجذاب بين الركيزة والموقع النشط،مما يمنع الإنزيم من تأديئة وظيفته على النحو الملائم. وبالإضافة إلى ذلك،يؤثر نوعا المثبطات بصورة مختلفة على معدل التفاعل الكيميائي.بالمقارنة مع معدل التفاعل الإنزيمي الطبيعي نجد أن التفاعل الذي يتضمن مثبط تنافسي يستغرق وقت أطول للوصول إلى السرعة القصوى،أقصى معدل للتفاعل،وقد تحتاج إلى مزيد من الركيزة لفعل ذلك،ولابد ان يكون هناك كمية كافية من الركيزة لكي تتغلب باستمرار على المُثبط للوصول إلى الموقع النشط. وعلى الجانب الآخر،المثبط اللا تنافسي لن يسمح بوصول المعدل إلى السرعة القصوى نتيجة لإنخفاض عدد الإنزيمات المتاحة للارتباط.

جوه ، إي تنغ ، ومارشا واي مورغان. "العلاج الدوائي لإدمان الكحول - لماذا وماذا ولماذا". علم الأدوية والعلاجات الغذائية 45 ، العدد 7 (2017): 865-882. [<a href = "https://doi.org/10.1111/apt.13965" >مصدر</a>]

تثبيط الانزيم

Enzyme Inhibition

المثبطات هي جزيئات تقلل من نشاط الإنزيم عن طريق الارتباط بالإنزيم. في الخلية التي تعمل بشكل طبيعي ، يتم تنظيم الإنزيمات بواسطة مجموعة متنوعة من المثبطات. يمكن للأدوية والسموم الأخرى أن تثبط الإنزيمات. ترتبط بعض المثبطات بالموقع النشط للإنزيم ، بينما يمنع البعض الآخر النشاط الإنزيمي من خلال الارتباط بمواقع أخرى على بنية البروتين.

تشغل المثبطات التنافسية الموقع النشط للإنزيمات ، مما يجعلها غير قادرة على استيعاب الركيزة. ومع ذلك ، يمكن لتركيزات عالية بما فيه الكفاية من الركيزة أن تتفوق على المثبط. ونتيجة لذلك ، فإن المثبطات التنافسية تبطئ معدل التفاعل الأولي للإنزيمات ولكنها لا تؤثر على المعدل الأقصى للإنزيم. أحد الأمثلة على مثبط تنافسي هو عقار ديسلفيرام ، الذي يستخدم لعلاج إدمان الكحول المزمن. عندما يتم تناول الكحول ، يتم تحويله عادةً إلى أسيتالديهيد ، والذي يتم تحويله بعد ذلك إلى أسيتيل كوأنزيم A عن طريق نزع هيدروجين الأسيتالدهيد. يرتبط ديسلفيرام بالموقع النشط للأسيتالدهيد ديهيدروجينيز ويحتله ، مما يجعل الإنزيم غير قادر على إجراء هذا التحويل. نتيجة لذلك ، يبدأ المريض الذي يتناول ديسلفيرام فوراً في الشعور بأعراض تشبه آثار الكحول ، مثل الصداع ، مما يقلل من استهلاك الكحول.

ترتبط المثبطات غير التنافسية بمواقع مميزة على الإنزيم ، بعيداً عن الموقع النشط. تسمى هذه المواقع متفارغ وعندما ترتبط الجزيئات بها ، يتغير شكل الموقع النشط بحيث يكون للإنزيم قابلية أقل للركيزة. نظراً لأن المثبطات غير التنافسية لا تشغل الموقع النشط ، فإن وجود ركيزة إضافية غير قادر على التغلب على التثبيط غير التنافسي ويكون الإنزيم غير قادر على تحقيق أقصى معدل تفاعل له.

عادة ما يكون الارتباط التساهمي بين المثبط والإنزيم لا رجوع فيه ، كما في حالة بعض السموم. تتفاعل معظم المثبطات التنظيمية النشطة عادة في الخلية مع الإنزيمات عن طريق التفاعلات الضعيفة. هذا النوع من الربط قابل للعكس ومفيد لتنظيم عمليات التمثيل الغذائي. يعد اكتشاف جزيئات جديدة لتثبيط الإنزيمات التي تنظم نمو الخلايا في السرطان بشكل تنافسي وغير تنافسي مجالاً نشطاً للبحث.

المثبطات هي جزيئات تقلل من نشاط الإنزيم عن طريق الارتباط بالإنزيم. في الخلية التي تعمل بشكل طبيعي ، يتم تنظيم الإنزيمات بواسطة مجموعة متنوعة من ...

Education

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Biology

علم الأحياء

Cellular Processes

العمليات الخلوية

Metabolism

عملية التمثيل الغذائي (الأيض)

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

what is metabolism?

Metabolism, Energy, and Cell Reactions

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first law of thermodynamics

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second law of thermodynamics

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kinetic energy

Motion as a Source of Energy

Kinetic energy is the energy of motion. It appears when an object is moving and can do work or cause change. A waterfall is one clear example. Water behind a dam has potential energy, but when it rushes downward, that moving water has kinetic energy. When the water reaches the bottom and stops moving, its energy can become potential energy again. Kinetic energy also shows up in living systems. Plants absorb light particles, called photons, which move very fast and help create chemical energy...

potential energy

Stored Energy in Motion and Bonds

Stored energy in motion and bonds is called potential energy. It depends on the structure of an object or the position of matter in space. Raising a kettlebell changes its location and increases its potential energy. A stretched rubber band also stores potential energy, which can later change into kinetic energy. Chemical bonds between atoms hold another form of stored energy called chemical energy. These bonds involve attractive forces, and that energy can change into other forms during a...

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Gibbs Free Energy in Chemical Reactions

Gibbs free energy is a measure of useful energy that can be taken from a chemical reaction to do work. It is written as G and named for scientist Gibbs, who discovered it. This energy is what remains after entropy is considered. A reaction can either take in energy or release it. Reactions that absorb energy are called endergonic reactions. Reactions that release energy are called exergonic reactions. The direction of energy flow helps show which type of reaction is happening. Plants carry...

activation energy

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phosphorylation

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Enzymes speed up many chemical reactions in cells. They are biological catalysts, so they increase reaction speed without being consumed or permanently changed. They do this by lowering the activation energy needed to turn reactants into products. Enzymes are proteins that usually work by binding to a substrate, which is the reactant molecule they act on. They show substrate specificity, meaning they bind only certain substrates. This specificity depends mainly on the shape and chemical...

enzyme kinetics

Substrate Effects on Enzyme Rates

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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...

feedback inhibition

How Cells Control Product Buildup

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allosteric regulation

Allosteric Control of Enzyme Speed

Allosteric control changes enzyme speed when a molecule binds to a site other than the active site. That alternate binding spot is called an allosteric site. An enzyme can have more than one allosteric site. This type of control can raise or lower enzyme activity. Many enzymes with allosteric control are metabolic enzymes. They help with the breakdown or the building of specific molecules in cells. In allosteric inhibition, the effector molecule causes a shape change that lowers the enzyme's...

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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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