3.2 Mechanism of Enzyme Action

Introduction

Enzymes are biological catalysts that speed up biochemical reactions without being consumed. They work by lowering the activation energy required for a reaction to occur. The mechanism of enzyme action involves the formation of an enzyme-substrate complex, conversion of substrate to product, and release of the product.

Definition

Mechanism of Enzyme Action: The mechanism of enzyme action is the process by which an enzyme binds to its substrate, converts it into product, and releases the product, allowing the enzyme to be reused.

In simple words: The mechanism of enzyme action is how enzymes work to speed up chemical reactions.

Core Concept

• The substrate first binds to the active site of the enzyme to form an enzyme-substrate (ES) complex.
• Then the substrate is converted into product while it is attached to the enzyme (enzyme-product complex, EP).
• Finally, the product is released, thus allowing the enzyme to start all over again.

General Equation:

E + Senzyme + substrate ⇌ ESenzyme-substrate complex ⇌ EPenzyme-product complex → E + Penzyme + product

Detailed Explanation

Steps in Enzyme Action

• The substrate binds to the active site of the enzyme.
• This binding is through non-covalent interactions:
• Hydrogen bonds
• Ionic bonds
• Hydrophobic interactions
• Van der Waals forces
• The enzyme-substrate complex is formed.

• The substrate undergoes a chemical reaction while attached to the enzyme.
• The enzyme lowers the activation energy of the reaction.
• The substrate is converted into product.
• The enzyme-product complex (EP) is formed.

• The product is released from the enzyme.
• The enzyme returns to its original state.
• The enzyme is ready to catalyze another reaction.

Key Features of Enzyme Action

• Enzymes are not consumed in the reaction.
• Enzymes are highly specific – they act on specific substrates.
• Enzymes lower activation energy – they speed up reactions.
• Enzymes are reusable – they can catalyze multiple reactions.
• Enzymes are affected by temperature and pH – they have optimal conditions.

Models of Enzyme Action

There are two main models to explain the mechanism of enzyme action:

• Lock and Key Model
• Induced Fit Model