Question

How the concentration of Isoleucine effects the activity of threonine deaminase in feedback inhibition?

Answer 1

 Feedback inhibition

• Enzymes are biological catalysts that speed up the chemical reaction by lowering activation energy, without undergoing any permanent change by itself.
• The enzyme has allosteric site and active site and the enzyme binds to the substrate.
• The active site is the 3D region, where the substrate binds to form enzyme substrate complex and later transforms it into the product.
• Allosteric site is 3D regulatory site of an enzyme other than active site.
• Substrate binding to the allosteric site induces a conformational change in the active site.
• Substrate 1 binds with the active site of enzyme 1 and forms enzyme substrate complex which is followed by the formation of product 1.
• This product 1 binds to the active site of enzyme 2 and forms a enzyme substrate complex and followed by the formation of product 2.
• The product 2 binds to the active site of enzyme 3 and results in product 3 .
• This product 3 acts as a substrate for enzyme 4 and forms the end product and this is no longer required in the cell.
• The end product binds to the allosteric site of the enzyme 1 causes a conformational change on the active site.
• Now when the initial substrate try to bind to the active site of enzyme 1, due to conformational change of active site by the binding of end product to allosteric site of enzyme 1, there will inhibition in the formation of further product formation.
• This is called Feedback inhibition.
• The amino acid threonine is converted to isoleucine by a series of five reactions.
• When there is a high amount of isoleucine, it binds to the enzyme threonine deaminase, which is responsible for the first step in this reaction.
• As the concentration of isoleucine builds up, it binds to the allosteric site of the first enzyme in the chain, i.e., threonine deaminase, which acts as a non-competitive inhibitor.
• The enzyme Isoleucine is known to be a very effective inhibitor and stabilizer of threonine deaminase.
• The feedback inhibition is useful in regulating the level of final product.
• In the above experiment, when the amount of isoleucine is nil, there will be no inhibition and the activity of threonine deaminase is very high.
• When the amount of isoleucine is low, there will be a low inhibition, and the activity of threonine deaminase is high.
• When the amount of isoleucine is medium, there will be a medium inhibition, and the activity of threonine deaminase is moderate.
• When the amount of isoleucine is high, there will be a high  inhibition, and the activity of threonine deaminase is completely very low.

 

The inhibition of an enzyme, controlling an early stage of a series of biochemical reactions by the end product is called Feedback inhibition.