Mechanism of Action of Enzymes: Study Notes

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Mechanism of Enzyme Action

Activation Energy is the energy required to start a chemical reaction. Enzymes help to lower the activation energy required for a reaction, thereby speeding up the process.

Enzymes are highly specific in their action, and this specificity was first proposed by Fischer in 1890. He suggested that the reason for this specificity is the precise shape of the enzyme, which allows it to bind with specific substrates.

• This is known as the 'Lock and Key' Hypothesis, where the enzyme is compared to a lock and the substrate to a key. The substrate fits perfectly into the enzyme’s active site (the "lock"), which has a complementary shape to the substrate (the "key").
• The Active Site is the region of the enzyme where the substrate binds and reacts.

However, in 1959, Koshland proposed a modification to this model, known as the 'Induced Fit' Hypothesis. According to Koshland, the enzyme's active site is flexible and can change its shape to better fit the substrate once the substrate begins binding.

Key Points of Enzyme Action:

• The active site is made up of specific amino acids that mold into the ideal shape when interacting with the substrate. This shape alteration enables the enzyme to catalyze the reaction more effectively.
• As the substrate binds to the enzyme, a transitional intermediate is formed. This intermediate is highly unstable, which lowers the activation energy, allowing the reaction to proceed more efficiently.

Induced Fit vs. Lock and Key

Induced Fit:

• Definition: Explains enzyme-substrate binding when they are not complementary in shape.
• Shape Before Binding: The shapes are not complementary before binding.
• Nature of Binding: The binding is flexible.
• Proposed By: Daniel E. Koshland.
• Active Site: The active site is dynamic and adjusts to the substrate.

Lock and Key:

• Definition: Explains the binding of perfectly matching substrate and enzyme for a reaction.
• Shape Before Binding: The shapes are complementary with each other before binding.
• Nature of Binding: The binding is strong and rigid.
• Proposed By: Emil Fischer.
• Active Site: The active site is static and unchanging.

In summary, the Induced Fit Hypothesis provides a dynamic explanation of enzyme-substrate interaction, where the enzyme adjusts its shape upon substrate binding to create a perfect fit, while the Lock and Key Hypothesis describes a rigid, complementary interaction between the enzyme and substrate from the start. Both models highlight the enzyme's role in lowering activation energy and catalyzing biochemical reactions effectively.

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