Enzyme Inhibition: Study Notes

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Types of Enzyme Inhibition

1. Competitive Inhibition

In competitive inhibition, an inhibitor molecule that closely resembles the enzyme’s substrate competes for the enzyme's active site. When the inhibitor binds to the active site, it blocks the substrate from binding, thus preventing the reaction from occurring. A common example of competitive inhibition is Penicillin, which interferes with the enzyme involved in bacterial cell wall synthesis, ultimately inhibiting bacterial growth.

Competitive inhibition can be reversed by increasing the concentration of the substrate. The higher substrate concentration outcompetes the inhibitor for access to the enzyme’s active site, allowing the reaction to proceed as normal.

2. Non-competitive Inhibition

In non-competitive inhibition, the inhibitor binds to a site other than the active site, known as the allosteric site. This binding causes a conformational change in the enzyme, altering its shape and reducing its ability to catalyze the reaction effectively. A well-known example of non-competitive inhibition is feedback inhibition, a mechanism where the product of a metabolic pathway inhibits the activity of an enzyme earlier in the pathway, thereby regulating the production of the product.

Because the inhibitor does not compete for the active site, increasing the substrate concentration does not overcome the inhibition. Instead, the enzyme’s overall effectiveness is reduced.

3. Un-competitive Inhibition

Un-competitive inhibition occurs when an inhibitor specifically binds to the enzyme-substrate complex (E-S complex), preventing the reaction from completing. This form of inhibition is often observed in multi-substrate reactions, where the inhibitor stabilizes the E-S complex, preventing the release of products. Unlike competitive inhibition, un-competitive inhibition only occurs after the substrate has bound to the enzyme.

This type of inhibition reduces both the maximum rate of the reaction and the apparent affinity of the enzyme for its substrate.

4. Feedback Inhibition

Feedback inhibition is a form of non-competitive inhibition where the end product of a metabolic pathway inhibits the enzyme responsible for catalyzing an earlier step in the pathway. This regulatory mechanism allows cells to control the concentration of metabolic products by slowing down the pathway when sufficient product has been produced. Once the concentration of the product decreases, the enzyme activity can be restored.

Feedback inhibition is crucial for maintaining homeostasis in cells and prevents the overproduction of certain compounds.

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