End-product inhibition

End-product inhibition is a type of enzyme inhibition where the product of a metabolic pathway inhibits an enzyme that acts early in the pathway, thus preventing overproduction of the product. This is a form of negative feedback and is an important regulatory mechanism in cells.

Mechanism

In end-product inhibition, the end-product of a metabolic pathway acts as an allosteric inhibitor for one of the enzymes in the pathway. This enzyme is usually the first rate-limiting enzyme in the pathway. The end-product binds to the allosteric site of the enzyme, changing its shape and reducing its catalytic activity. This prevents the enzyme from converting its substrate into the next metabolite in the pathway, effectively shutting down the pathway when the levels of the end-product are high.

Role in Metabolism

End-product inhibition plays a crucial role in maintaining homeostasis within cells. By preventing overproduction of metabolic products, it helps to ensure that resources are not wasted and that the cell's internal environment remains stable. It also allows the cell to respond quickly to changes in conditions. For example, if the cell suddenly needs more of a particular metabolite, the end-product will be used up, relieving the inhibition and allowing the pathway to start up again.

Examples

One of the most well-known examples of end-product inhibition is the regulation of the glycolysis pathway. In this pathway, the end-product pyruvate inhibits the enzyme phosphofructokinase, which is the first rate-limiting enzyme in the pathway. This prevents overproduction of pyruvate when energy levels in the cell are high.

Another example is the synthesis of isoleucine from threonine in bacteria. The end-product isoleucine inhibits the enzyme threonine deaminase, which is the first step in the pathway.

See also

• Feedback inhibition
• Enzyme kinetics
• Metabolic pathway
• Allosteric regulation