What is the Difference Between Allosteric Site and Active Site

The key difference between allosteric site and active site is that an allosteric site is a region of an enzyme that allows activator or inhibitor molecules to bind to the enzyme and either activate or inhibit enzyme activity, while an active site is a region of an enzyme where substrate molecules bind and catalyze the reaction resulting in the production of particular products.

Enzymes are proteins that help biochemical reactions in the human body. One of the most important roles of enzymes is digestion. Enzymes also help with breathing, building muscles, nerve function, and getting rid of toxins in the body. Enzymes have different areas in the structure where molecules can bind and catalyze reactions. Allosteric sites and active sites are two different areas in the enzyme structure that facilitate molecules’ binding and subsequent chemical reactions.

CONTENTS

1. Overview and Key Difference
2. What is an Allosteric Site  
3. What is an Active Site
4. Similarities – Allosteric Site and Active Site
5. Allosteric Site vs Active Site in Tabular Form
6. Summary – Allosteric Site vs Active Site

What is an Allosteric Site?

Allosteric site is a region of an enzyme that allows activator or inhibitor molecules to bind to the enzyme that either activate or inhibit enzyme activity. Enzymes work at different temperatures depending on the environment. Several factors, including hotness, coldness, pH, location in the body, and other substances, influence enzyme activity in addition to the main substrate. There are some substances that bind to the enzyme at a different site other than the normal active site. These sites that allow other substances binding are known as allosteric sites. Allosteric sites allow other substances to either activate, inhibit, or turn off enzyme activity. This happens when other substances bind to the allosteric site and change the confirmation or shape of the enzyme.

An example of allosteric activator is oxygen binding to haemoglobin. Allosteric binding of oxygen to haemoglobin changes the confirmation of haemoglobin and increases its affinity for more oxygen. This process ensures haemoglobin will transport the maximum amount of oxygen from oxygen-rich areas like the lungs. Another example of allosteric inhibitor is an ATP in cellular respiration. One important enzyme involved in glycolysis is phosphofructokinase. This enzyme converts ADP to ATP. When there is too much ATP in the cell, ATP serves as an allosteric inhibitor that binds to the allosteric site of phosphofructokinase to slow down the conversion of ADP to ATP.

What is an Active Site?

Active site is the region of an enzyme where substrate molecules bind and undergo a reaction to make products. Active site is further divided into two distinct sites: binding site and calalytic site. In the binding site, amino acid residues of the active site form temporary bonds with the substrate. On the other hand, in the catalytic site, amino acid residues of the active site catalyse a reaction of that substrate.

The active site of an enzyme usually has three to four amino acids, while other amino acids in the enzyme are required to maintain the tertiary structure of the enzyme. An active site of an enzyme can catalyze a reaction repeatedly as residues are not changed at the end of the reaction. This process is achieved normally by lowering the activation energy of the reaction. Therefore, more substrates have enough energy to undergo a chemical reaction.

What are the Similarities Between Allosteric Site and Active Site?

• Allosteric site and active site are two different areas in the enzyme structure that facilitate molecules’ binding and subsequent chemical reactions.
• Both sites are made up of amino acids.
• These sites have a unique shape.
• Both sites are very important for enzyme activity and enzyme-catalyzed reaction.

What is the Difference Between Allosteric Site and Active Site?

Allosteric site is a region of an enzyme that allows activator or inhibitor molecules to bind to the enzyme in order to activate or inhibit enzyme activity, while active site is a region of an enzyme where substrate molecules bind and catalyze the reaction resulting in the production of particular products. Thus, this is the key difference between allosteric site and active site. Furthermore, allosteric sites are only present in allosteric enzymes, while active sites are present in all enzymes.

The below infographic presents the differences between allosteric site and active site in tabular form for side by side comparison.

Summary – Allosteric Site vs Active Site

Allosteric site and active site are two different regions in the enzyme structure. Allosteric site is a region of an enzyme that allows activator or inhibitor molecules to bind to the enzyme that either activate or inhibit enzyme activity, while active site is a region of an enzyme where substrate molecules bind and catalyze the reaction resulting in the production of particular products. So, this is the key difference between allosteric site and active site.

Reference:

1. “Active Site.” An Overview | ScienceDirect Topics.
2. “What is an Allosteric Site of the Enzyme? – Definition & Biology.” Study.com.

Image Courtesy:

1. “Figure 06 05 05” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “SI active site” By Areid3 – Own work (CC BY-SA 4.0) via Commons Wikimedia