The key difference between allosteric and non-allosteric enzymes is that allosteric enzymes have allosteric sites other than their active sites for the binding of regulatory molecules, while non-allosteric enzymes have only an active site to bind with the substrate.
There are different ways of enzyme regulation. Allosteric regulation is one such form of enzyme regulation. Allosteric regulation is facilitated by enzymes called allosteric enzymes. Regulatory molecules bind to allosteric sites possessed by the enzyme and regulate the enzymatic activity. Therefore, allosteric enzymes are known as regulatory enzymes as well. The speciality of the allosteric enzymes is that they possess additional sites other than the main active site.
CONTENTS
1. Overview and Key Difference
2. What are Allosteric Enzymes
3. What are Non-allosteric Enzymes
4. Similarities – Allosteric vs Non-allosteric Enzymes
5. Allosteric vs Non-allosteric Enzymes in Tabular Form
6. Summary – Allosteric vs Non-allosteric Enzymes
What are Allosteric Enzymes?
Allosteric enzymes are a type of enzyme that possess allosteric sites for the binding of regulatory molecules. These sites are located in the different protein subunits of the enzyme. A regulatory molecule can be an inhibitor or an activator. When an inhibitor binds to the enzyme, the enzyme activity decreases. When an activator binds to the enzyme, enzymatic function increases. This type of regulation of enzymatic activity is known as allosteric regulation. An allosteric enzyme is specific to its substrate and its regulatory molecules (modulators). The interaction of the regulatory molecule/modulator with the enzyme is reversible and non-covalent. A reaction catalyzed by an allosteric enzyme shows a sigmoidal curve.
Figure 01: Allosteric Inhibition
Allosteric regulation takes place as a feedback mechanism. In negative feedback inhibition, the regulatory molecule is an inhibitor, and it inhibits the reaction. In a positive feedback mechanism, an effector molecule or activator which binds to the allosteric site increases the rate of reaction. The binding of the allosteric modulator to an allosteric enzyme changes the conformation of the protein, thus affecting its function. Pyruvate kinase, ribonucleotide reductase, aspartate transcarbamoylase and ADP-glucose pyrophosphorylase are several examples of allosteric enzymes.
What are Non-allosteric Enzymes?
Non-allosteric enzymes are the enzymes that do not process allosteric sites other than the active site. Therefore, they are simple enzymes that have only one enzyme active site. These enzymes are substrate-specific enzymes. They are also non-regulatory enzymes. Their reactions show a hyperbolic curve.
Figure 02: Hyperbolic Curve shown by a Non-allosteric Enzyme
When there is a competitive inhibitor, the reaction rate decreases. A competitive inhibitor is similar to the substrate. Hence, it competes with the substrate for binding with the active site. When the substrate fails to bind with the active site, the substrate-enzyme complex cannot be formed, so the reaction rate decreases.
What are the Similarities Between Allosteric and Non-allosteric Enzymes?
- Allosteric and non-allosteric enzymes are two types of enzymes.
- They are made up of proteins.
- They catalyze biochemical reactions in living cells.
- Both types of enzymes remain unchanged at the end of the reaction.
- A small concentration of these enzymes is enough to catalyze a reaction.
- They are sensitive to changes in pH and temperature.
What is the Difference Between Allosteric and Non-allosteric Enzymes?
An allosteric enzyme is an enzyme that has an additional site called regulatory site or allosteric site for the binding of a regulatory molecule. A non-allosteric enzyme is a simple enzyme that has only an active site for the binding of its substrate. So, this is the key difference between allosteric and non-allosteric enzymes.
The following infographic lists the differences between allosteric and non-allosteric enzymes in tabular form for side by side comparison.
Summary – Allosteric vs Non-allosteric Enzymes
The allosteric enzyme is a regulatory enzyme that possesses an allosteric site other than the active site. Hence, a regulatory molecule can bind with the allosteric site and regulate the enzymatic activity. In contrast, the non-allosteric enzyme does not have an allosteric site. It has only an active site. Non-allosteric enzymes are not regulatory enzymes. Allosteric enzymes are both substrate and regulatory molecule specific, while non-allosteric enzymes are substrate-specific. Thus, this is the summary of the difference between allosteric and non-allosteric enzymes.
Reference:
1. “Enzyme Regulation (Article).” Khan Academy.
2. “Enzymes.” Lumen.
Image Courtesy:
1. “Allosteric inhibition” By [[:en:User:{{{1}}}|{{{1}}}]] at the English-language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Michaelis Menten curve 2” By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia
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