B.Sc. 2nd year Microbiology

Assistant Professor- Shubham Shukla
Department of Microbiology
Mechanism of Enzyme Action

The mechanism of enzyme action is the process by which enzymes act on their substrates and convert them into products.

Steps in Enzyme Action

1. Formation of the Enzyme–Substrate Complex (E–S Complex)
   The substrate binds to the enzyme's active site through non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic forces.
2. Catalytic Conversion
   The enzyme stabilizes the transition state and converts the substrate into product by lowering the activation energy barrier.
3. Release of Product
   Once the product is formed, it no longer fits perfectly in the active site and is released.
4. Regeneration of Enzyme
   The enzyme returns to its original state, ready to catalyze another reaction.
   

Theories of Enzyme Action

Lock and Key Model (Fischer, 1894)

• The enzyme's active site is a rigid structure complementary in shape to the substrate.
• The substrate fits precisely like a key fits into a lock.
• This model explains enzyme specificity but not flexibility.
• Limitation: Does not explain how enzymes can change shape during catalysis.
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Induced Fit Model (Koshland, 1958)

• The enzyme's active site is flexible and undergoes a conformational change when the substrate binds.
• This adjustment enhances the enzyme's ability to catalyze the reaction efficiently.
• Most accepted model as it explains enzyme flexibility, specificity, and catalytic efficiency.
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Would you like me to also create a diagram showing enzyme action (substrate binding, conversion, product release) so you can visualize the process better?