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

כימיקלים מסוימים יכולים לווסת את פעולת האנזימים על ידי עיכוב, או חסימת, תפקודם. למעכבי אנזימים יש שתי צורות שונות:תחרותיים ולא-תחרותיים. מעכב תחרותי דומה דיו לסובסטרט הייחודי לאנזים ויכול להיקשר לאתר הפעיל ולחסום היקשרות הסובסטרט.פעולה זו מקטינה למעשה את מספר האנזימים הזמינים לקשירת הסובסטרט. לעומת זאת, מעכב לא-תחרותי נקשר הרחק מהאתר הפעיל, אך עדיין משפיע עליו, למשל, על ידי שינוי צורת האנזים שבתורו מפחית את זיקת הקישור בין הסובסטרט לאתר הפעיל, ומונע מהאנזים לתפקד כראוי. בנוסף, שני סוגי המעכבים משפיעים באופן דיפרנציאלי על קצב התגובה הכימית.לעומת בקרה, קצב של תגובה אנזימטית רגילה, לתגובה עם מעכב תחרותי יידרש זמן רב יותר Vmax-כדי להגיע ל, קצב התגובה המקסימלי, וכמות סובסטרט רבה לשם כך, מכיוון שיש צורך בסובסטרט המספיק כדי לגבור באופן עקבי על המעכב בגישה לאתרים הפעילים. מצד שני, מעכב לא-תחרותי Vmax-לא יאפשר לקצב להגיע ל, מכיוון שמספר האנזימים הזמינים לקשירה מצטמצם.

גו, אי טנג ומרשה י. מורגן. "טיפול תרופתי לתלות באלכוהול – הלמה, המה, והאיפה". פרמקולוגיה וטיפולים 45, מס '7 (2017): 865-882. [<a href="https://doi.org/10.1111/apt.13965">מקור</a>]

עיכוב אנזים

Enzyme Inhibition

<div style="direction:rtl">מעכבים הם מולקולות המפחיתות את פעילות האנזים על ידי קשירה לאנזים. בתא המתפקד כרגיל, האנזימים מווסתים על ידי מגוון מעכבים. תרופות ורעלים אחרים יכולים גם לעכב אנזימים. מעכבים מסוימים נקשרים לאתר הפעיל של האנזים, בעוד שאחרים מעכבים פעילות אנזימטית על ידי קישור לאתרים אחרים במבנה החלבון. מעכבים תחרותיים תופסים את האתר הפעיל של אנזימים, מה שהופך אותם ללא מסוגלים להכיל את הסובסרט (מצע). עם זאת, ריכוזים גבוהים מספיק של המצע יכולים להתחרות על המעכב; כתוצאה מכך, מעכבים תחרותיים מאטים את קצב התגובה הראשוני של האנזימים אך אינם משפיעים על הקצב המרבי של האנזים. דוגמה אחת של מעכב תחרותי היא התרופה דיסולפירם, המשמשת לטיפול באלכוהוליזם כרוני. כאשר אלכוהול נבלע, הוא הופך בדרך כלל לאצטאלדהיד, אשר הופך לאחר מכן לאצטיל קואנזים A על ידי אצטלדהיד דהידרוגנאז. דיסולפירם נקשר ותופס את האתר הפעיל של אצטלדהיד דהידרוגנאז, מה שהופך את האנזים ללא מסוגל לבצע המרה זו. כתוצאה מכך, חולה הנוטל דיסולפירם מתחיל מיד לחוות תסמינים דמויי הנגאובר, כגון כאב ראש, ובכך מפחית את צריכת האלכוהול. מעכבים לא תחרותיים נקשרים לאתרים שונים באנזים, הרחק מהאתר הפעיל. אלה נקראים אתרים אלוסטריים וכאשר מולקולות נקשרות אליהם, צורת האתר הפעיל משתנה כך שלאנזים יש זיקה נמוכה יותר לסובסטרט. מכיוון שמעכבים לא תחרותיים אינם תופסים את האתר הפעיל, נוכחות של סובסטרט נוסף אינה מסוגלת להתגבר על עיכוב לא תחרותי והאנזים אינו מסוגל להשיג את קצב התגובה המרבי שלו. קישור קוולנטי בין מעכב לאנזים הוא בדרך כלל בלתי הפיך, כמו במקרה של כמה רעלים. רוב המעכבים הרגולטוריים הפעילים בדרך כלל בתא מתקשרים עם אנזימים על ידי אינטראקציות חלשות. סוג זה של קשירה הוא הפיך ושימושי לוויסות תהליכים מטבוליים. חקר מולקולות חדשות כדי לעכב באופן תחרותי ולא תחרותי אנזימים המסדירים את צמיחת התאים בסרטן הוא תחום מחקר פעיל.</div>

מעכבים הם מולקולות המפחיתות את פעילות האנזים על ידי קשירה לאנזים. בתא המתפקד בדרך כלל, אנזימים מוסדרים על ידי מגוון רחב של ...

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KEY TERMS AND CONCEPTS

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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

what is metabolism?

Metabolism, Energy, and Cell Reactions

Metabolism is the set of chemical reactions that happen in a cell. It includes anabolism, which builds molecules, and catabolism, which breaks them down. These reactions help cells manage energy and keep life processes running. Cells use metabolism to turn food into energy, make cell parts, and remove waste products. Food stores potential energy in the bonds between atoms. Catabolic pathways break large food molecules into smaller ones and release that energy. Anabolic pathways use that energy...

first law of thermodynamics

Energy Flow in a Food Web

Energy flow in a food web shows the First Law of Thermodynamics in action. Energy cannot be created or destroyed. It can only change form as it moves through living things and the environment. Sunlight is the starting point. Plants capture radiant energy from the sun during photosynthesis and turn it into chemical energy stored in complex carbohydrates. At the same time, oxygen is released into the atmosphere. Herbivores eat the plants and use those sugars during digestion. The energy is...

second law of thermodynamics

Entropy in Food Web Energy Flow

The Second Law of Thermodynamics explains why entropy increases as energy moves through a system. Entropy means the amount of disorder in a system. Each time energy is transferred or transformed, some energy is lost as unusable heat. That heat can raise the motion of nearby molecules for a short time and make the surroundings less ordered and more random. This idea also appears in a food web. Primary producers, such as plants, take in energy from the sun and make food. During this process,...

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...

free energy

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

How Catalysts Lower Reaction Barriers

Activation energy is the minimum energy a chemical reaction needs to keep going. When the activation energy is higher, the reaction usually happens more slowly. Adding heat can speed the reaction because molecules move faster and collide more often. As reactants collide, bonds break and the reaction moves through an uphill phase. That step creates the transition state, which is an unstable, high-energy state of the reactants. After that, new bonds form, products appear, and free energy is...

hydrolysis of atp

ATP Breakdown and Energy Release

ATP breakdown releases energy for cell work. Adenosine triphosphate, or ATP, can lose one or two phosphate groups when water is added. This hydrolysis reaction is exergonic, which means it releases energy that the cell can use. When one phosphate group is removed, ATP becomes ADP, or adenosine diphosphate. Inorganic phosphate is also released. ADP can then be hydrolyzed again to form AMP, or adenosine monophosphate, after a second phosphate group is removed. ATP has a clear structure. It is...

phosphorylation

Phosphorylation and Protein Control

Phosphorylation helps control how proteins work in cells. It is the addition or removal of phosphate groups, and it is the most common chemical change that regulates cellular processes. These changes can alter a protein’s structure, activity, stability, location inside the cell, and interactions with other proteins. During phosphorylation, protein kinases move the terminal phosphate group from ATP to a specific amino acid side chain on a target protein. The amino acids most often...

induced-fit model

How Enzymes Adjust to Their Substrates

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

Enzyme kinetics examines how enzymes change the rate of a reaction. Enzymes speed reactions by lowering the activation energy of the reactants. The reaction rate is the speed at which an enzyme turns reactants into products, and it can be affected by several factors, including the number of available reactants. Scientists often study enzyme kinetics in a test tube with a fixed amount of enzyme. When more substrate, or reactant, is added, the reaction rate increases because the enzyme can make...

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

Cells use enzymes to run biochemical reactions and make the products they need. These reactions are happening constantly, and enzymes speed them up so they happen fast enough to matter. Enzyme activity also has to be regulated. Cells need the right amounts of starting materials, intermediate metabolites, and final products. If these substances build up too much or drop too low, the cell can be harmed. That is why cells use control systems to keep metabolic levels balanced. One important...

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...

cofactors and coenzymes

Enzyme Helpers: Metals, Vitamins, and More

Enzyme helpers are needed for many enzymes to work properly. These helpers fall into two groups: cofactors and coenzymes. Cofactors are metallic ions, while coenzymes are non-protein organic molecules. Both can be tightly bound to an enzyme or attach only when the substrate binds. Cofactors are common in mature proteins, appearing in about 30% of them. They are often added as the enzyme folds and help with catalytic activity. Magnesium is one important cofactor, and it is needed by more than...

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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