Key Difference – Competitive vs Noncompetitive Inhibition
The action of inhibitors can be found in two types as competitive inhibitors and noncompetitive inhibitors based on the place on the enzyme where the inhibitor binds. The key difference between competitive inhibition and noncompetitive inhibition is that in competitive inhibition, binding of an inhibitor prevents the binding of the target molecule with the active site of the enzyme whereas, in noncompetitive inhibition, an inhibitor reduces the activity of an enzyme.
An enzyme is a macromolecule that can act as a biological catalyst. Enzymes have regions known as active sites. The active site of an enzyme is the location where a target molecule binds. This molecule is known as a substrate. The substrate bind with the active site and undergoes chemical reactions. This gives a maximum yield at a short time period. The enzyme can also be recycled and reused. Inhibitors are compounds that can prevent the substrates from undergoing a certain chemical reaction.
CONTENTS
1. Overview and Key Difference
2. What is Competitive Inhibition
3. What is Noncompetitive Inhibition
4. Side by Side Comparison – Competitive vs Noncompetitive Inhibition in Tabular Form
5. Summary
What is Competitive Inhibition?
Competitive inhibition is a type of enzyme inhibition in which an inhibitor binds to the active sites of an enzyme, preventing the substrate from binding to the enzyme. The active site is blocked by the inhibitor, so there is no space for the substrate to bind to the enzyme.
In this inhibition type, the inhibitors that are bound to the active sites are similar to the shape of the substrate molecules (if not, the inhibitors cannot bind with the active site because the shape of the active site does not fit the shape of the substrate). Therefore, the enzyme active site cannot bind with both inhibitor and the substrate at the same time. This makes the inhibitor to compete with the substrate to bind to the active site, which gives the name competitive inhibition.
Figure 01: Competitive Inhibition in a Diagram
Competitive inhibition can be prevented by adding many substrate molecules. This increases the probability of active sites meeting substrates rather than inhibitor molecules. Most competitive inhibitors are bound to the active site reversibly. This is because the inhibitor does not change the shape of the active site.
What is Noncompetitive Inhibition?
Noncompetitive inhibition is a type of enzyme inhibition in which an inhibitor reduces the activity of an enzyme. Here, the inhibitor can bind to the enzyme even if the substrate is already bound to the active site of that enzyme. Therefore the inhibitor does not bind to the active site. Hence, there is no competition between the substrate and the inhibitor; this inhibition is thus known as noncompetitive inhibition. Then, the substrate and the inhibitor can be found on an enzyme at the same time.
Figure 2: Noncompetitive Inhibition in a Diagram
When the inhibitor is bound to the enzyme along with the substrate, the substrate cannot undergo the desired chemical reaction to give target products. Noncompetitive inhibitors often bind to the enzyme irreversibly. This is because the binding of the inhibitor changes the shape of the active site and the active site get deactivated.
The shape of the inhibitor is completely different from that of the substrate because the inhibitor does not compete for the active sites on the enzyme. The noncompetitive inhibitors bind with sites that are near an active site. This binding causes the alteration of the shape of the active site.
What is the Difference Between Competitive and Noncompetitive Inhibition?
Competitive Inhibition vs Noncompetitive Inhibition
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| Competitive inhibition is a type of enzyme inhibition in which an inhibitor binds to the active sites of an enzyme, preventing the substrate from binding to the enzyme. | Noncompetitive inhibition is a type of enzyme inhibition in which an inhibitor reduces the activity of an enzyme. |
| Competition with Substrate | |
| Competitive inhibitors compete with the substrate for active sites. | Noncompetitive inhibitors do not compete with the substrate for active sites. |
| Shape of the Inhibitor | |
| Competitive inhibitors have a similar shape to that of substrate | Noncompetitive inhibitors have a shape that is different from the shape of the substrate. |
| Occurrence on the Enzyme | |
| The substrate and the competitive inhibitor cannot be found on an enzyme at the same time. | The substrate and the noncompetitive inhibitor can be found on an enzyme at the same time. |
| Binding Method | |
| The binding of competitive inhibitors with the active site is reversible. | The binding of noncompetitive inhibitors with the active site is irreversible. |
| Effect on the Shape of the Active Site | |
| The shape of the active site does not change when a competitive inhibitor binds to the active site. | The shape of the active site changes when an inhibitor is bound to the enzyme. |
Summary – Competitive vs Noncompetitive Inhibition
The key difference between competitive inhibition and noncompetitive inhibition is that in competitive inhibition, binding of an inhibitor prevents the binding of the target molecule with the active site of the enzyme whereas, in noncompetitive inhibition, an inhibitor reduces the activity of an enzyme.
Reference:
1. “Competitive Inhibition.” Wikipedia, Wikimedia Foundation, 3 Mar. 2018, Available here.
2. “Non-Competitive Inhibition.” Wikipedia, Wikimedia Foundation, 25 Mar. 2018, Available here.
3. “Active Site.” Wikipedia, Wikimedia Foundation, 25 Mar. 2018, Available here.
Image Courtesy:
1. “Competitive inhibition” By Authored by Jerry Crimson Mann, modified by TimVickers, vectorized by Fvasconcellos – Image:Competitive inhibition.png (Public Domain) via Commons Wikimedia
2. “Allosteric competitive inhibition 3” By srhat (talk · contribs)File:Comp_inhib.svg:SVG version:Srhat (talk · contribs)PNG version:Jerry Crimson Mann at en.wikipedia – File:Comp_inhib.svg (Public Domain) via Commons Wikimedia