The main difference between competitive and noncompetitive antagonism is that competitive antagonism is the binding of the antagonist to the same site as the agonist, whereas noncompetitive antagonism is the binding of the antagonist to the allosteric site, which is the agonist.
Competitive and noncompetitive antagonists are two types of antagonists that reduce the action of another drug.
Key Areas Covered
1. What is Competitive Antagonism
– Definition, Facts, Features
2. What is Noncompetitive Antagonism
– Definition, Facts, Features
3. Similarities Between Competitive and Noncompetitive Antagonism
– Outline of Common Features
4. Difference Between Competitive and Noncompetitive Antagonism
– Comparison of Key Differences
5. FAQ: Competitive and Noncompetitive Antagonism
– Answers to frequently asked questions
Key Terms
Competitive Antagonism, Noncompetitive Antagonism
What is Competitive Antagonism
Competitive antagonism is the binding of the antagonist to the binding site of the agonist. It binds to the active site of the enzyme. Therefore, both the agonist and the antagonist bind to the same recognition site. They compete with each other for the active site when agonist and antagonist are present concomitantly. Reversible competitive antagonism is a type of competitive antagonism that occurs with the elimination of the binding of the antagonist by increasing the concentration of the agonist. Examples of competitive antagonists include ach+, atropine, morphine, and naloxone.
Figure 1: Competitive Antagonism
What is Noncompetitive Antagonism
Noncompetitive antagonism is another type of antagonism in which the antagonist binds to the allosteric site of the enzyme. Since it does not bind to the active site of the enzyme, the antagonist in the noncompetitive antagonism does not compete with the agonist. Therefore, the antagonist in this type of antagonism changes the conformation of the enzyme, not allowing the binding of the agonist to the active site of the enzyme. Examples of noncompetitive antagonists include diazepam and bicuctaline.
Figure 2: Antagonist
Similarities Between Competitive and Noncompetitive Antagonism
- Competitive and noncompetitive antagonism are two antagonist types that are drugs.
- They inhibit the action of other drugs by binding to enzymes.
Difference Between Competitive and Noncompetitive Antagonism
Definition
Competitive antagonism refers to the binding of the antagonist to the same site as the agonist but does not activate it, thus blocking the agonist’s action. In contrast, noncompetitive antagonism refers to the binding of the antagonist, while still opposing the action of the agonist, does so without competing with it for the binding site.
Binding of the Antagonist
Competitive antagonist binds to the active site of the enzyme, while noncompetitive antagonist binds to the allosteric site of the enzyme.
Competing with the Agonist
Competitive antagonist competes with the agonist, while noncompetitive antagonist does not compete with the agonist.
Resembles
Competitive antagonist chemically resembles the agonist, while noncompetitive antagonist does not chemically resemble the agonist.
Dose
The effect of the agonist can be attained by increasing the dose of the agonist in competitive antagonism, while the effect of the agonist cannot be attained by increasing the dose of the agonist in noncompetitive antagonism.
Examples
Ach+, atropine, morphine, and naloxone are examples of competitive antagonism, while diazepam and bicuctaline are examples of noncompetitive antagonism.
FAQ: Competitive and Noncompetitive Inhibition
Which is the best example of non-competitive inhibition?
The action of cyanide on cytochrome oxidase is the best example of non-competitive inhibition. It binds to a place other than the active site, bringing conformational changes to the enzyme. Therefore, the binding of the cyanide prevents the transport of electrons from cytochrome c to oxygen.
Can an inhibitor be both competitive and noncompetitive?
A hybrid form of inhibition occurs by displaying characteristics of both competitive and noncompetitive inhibition. They are called mixed non-competitive inhibitors.
What are the 3 types of enzyme inhibitions?
Competitive, noncompetitive, and uncompetitive inhibitors are the three types of enzyme inhibition. Uncompetitive inhibitors do not bind to the enzyme until they associate with the substrate-enzyme complex.
Conclusion
In brief, competitive and noncompetitive antagonism are two antagonism types. They are drugs that bind to the enzymes, inhibiting the action agonists. Competitive antagonism is the binding of the antagonist to the active site of the enzyme, competing with the agonist. By increasing the dose of the agonist, the effect of the agonist can be attained in competitive antagonism. In comparison, noncompetitive antagonism is the binding of the antagonist to the allosteric site of the enzyme, not competing with the agonist. Also, the antagonist in the noncompetitive antagonism does not chemically resemble the agonist. Therefore, the main difference between competitive and noncompetitive antagonism is the type of binding of the antagonist to the enzyme.
References:
- Antagonism. Lesson 6. (n.d.).
Image Courtesy:
- “Antagonist 2” By JWSchmidt at English Wikipedia – Own Work (CC-BY SA 3.0) via Commons Wikimedia
- “Ligand response comparison” By Arthurfragoso – Own Work (CC0) via Commons Wikimedia
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