The main difference between allosteric and non-allosteric inhibition is that allosteric inhibition is a physiological process, whereas non-competitive inhibition is not a physiological process.
Allosteric and non-competitive inhibition are two types of inhibition processes of enzymes. Generally, enzyme inhibition is the major control mechanism of biological systems.
Key Areas Covered
1. What is Allosteric Inhibition
– Definition, Features, Importance
2. What is Non-competitive Inhibition
– Definition, Features, Importance
3. Similarities – Allosteric and Non-competitive Inhibition
– Outline of Common Features
4. Difference Between Allosteric and Non-competitive Inhibition
– Comparison of Key Differences
Key Terms
Allosteric Inhibition, Non-competitive Inhibition
What is Allosteric Inhibition
Allosteric inhibition is the inhibition of enzymes by binding small molecules called effector molecules at a site other than the enzyme’s active site. The binding site of molecules in the allosteric inhibition is also known as the allosteric site or regulatory site. However, the binding of effector or small molecules to the allosteric site allows the changing of the conformation of the enzyme. This, in turn, changes the dynamics of the enzyme. Meanwhile, allosteric activators are small molecules that increase the activity of the enzyme upon binding, while allosteric inhibitors are effector molecules that decrease the activity of the enzyme upon binding.
Figure 1: Competitive Inhibition
Furthermore, some examples of allosteric inhibition include control loops, feedback mechanisms of the downstream products, and feedforward from upstream substrates. Allosteric inhibition is particularly important for adjusting enzyme activity. Generally, the allosteric inhibition types include competitive, non-competitive, and uncompetitive inhibition. Competitive inhibition is a type of inhibition in which the inhibitor molecules compete with the substrate resembling the substrate. In comparison, in uncompetitive inhibition, effector molecules bind to the enzyme following the formation of the enzyme-substrate complex. Moreover, uncompetitive inhibition is important when two substrates or two products are available in enzymatic reactions.
What is Non-competitive Inhibition
Non-competitive inhibition is a type of reversible inhibition in which the inhibitor molecules bind to the enzyme-substrate complex at an allosteric site, a site other than the active site. Here, the binding of the inhibitor molecules to the allosteric site results in the conformational change in the active site of the enzyme. It alters the specificity of the active site to the corresponding substrate, making the active site unavailable for binding to the substrate. However, since noncompetitive inhibitors do not directly compete with the substrate, they do not change the substrate concentration.
Figure 2: Non-Competitive Inhibition
Moreover, cyanide is a poison that binds to an allosteric site of cytochrome oxidase, a carrier protein in the electron transport chain. It prevents ATP production through aerobic respiration, leading to death eventually.
Similarities Between Allosteric and Non-competitive Inhibition
- Allosteric and non-allosteric inhibition are two types of inhibition processes that inhibit enzymes by small molecules.
- Enzyme inhibition is a major control mechanism of biological processes.
Difference Between Allosteric and Non-competitive Inhibition
Definition
Allosteric inhibition refers to the slowing down of enzyme-catalyzed chemical reactions that occur in cells, while non-competitive inhibition refers to a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme.
Significance
Allosteric inhibition is a type of enzyme inhibition that allows the binding of small molecules to the enzyme non-other than the active site of the enzyme in order to change the activity of the enzyme while non-competitive inhibition allows the binding of inhibitor molecules, reducing the activity of the enzyme.
Correlation
The types of allosteric inhibition include competitive, non-competitive, or uncompetitive inhibition while non-competitive inhibition is a type of allosteric inhibition.
Importance
Allosteric inhibition is a physiological process while non-competitive inhibition is a non-physiological process.
Competition with the Substrate
Moreover, allosteric inhibition competes with the substrate while non-competitive inhibition does not compete with the substrate.
Action
Allosteric inhibition allows the binding of small molecules into the allosteric site or regulatory site, while non-competitive inhibition allows the binding of small molecules to non-substrate sites.
Conformational Change
Allosteric inhibition changes the conformation of the enzyme while non-competitive inhibition does not change the conformation of the enzyme.
Extent of Inhibition
Furthermore, allosteric inhibition allows the binding of more inhibitor molecules to increase the degree of inhibition while non-competitive inhibition does not have a different degree of inhibition.
Effect on Enzyme
Allosteric inhibition adjusts the activity of the enzyme while non-competitive inhibition keeps the enzyme non-functional.
Conclusion
In brief, allosteric and non-competitive inhibition are two types of inhibitory processes of enzymes. Allosteric inhibition is a physiological process allowing the binding of small molecules to sites non-other than the active site of the enzyme. Therefore, small molecules bind to the allosteric or regulatory site of the enzyme. Moreover, the degree of inhibition depends on the number of inhibitor molecules that bind to the enzyme molecule. In addition to that, allosteric inhibition adjusts the activity of the enzyme. In comparison, non-competitive inhibition is a non-physiological process that allows the binding of small molecules to the non-substrate sites reducing the activity of the enzyme. It also makes the enzyme non-functional. Therefore, the main difference between allosteric and non-competitive inhibition is the type of inhibition of enzymes.
References:
- “Enzyme regulation (article).” Khan Academy.
Image Courtesy:
- “Comp inhib” By :Srhat – Own work (CC BY-SA 3.0) via Commons Wikimedia
- “Non-competitive inhibition” By Srhat – Own Work (CC BY-SA 3.0) via Commons Wikimedia
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