6. ENZYMES

Enzymes are essential biological catalysts that control and speed up chemical reactions inside the body. Every process in the human body—digestion, energy production, detoxification, metabolism—requires enzymes to work efficiently. These notes explain enzymes in simple, clear language suitable for D.Pharmacy students.

ACTUAL NOTES:

Enzymes: Definition, Properties, Classification, Factors, Mechanism and Therapeutic Importance

Enzymes are essential biological catalysts that control and speed up chemical reactions inside the body. Every process in the human body—digestion, energy production, detoxification, metabolism—requires enzymes to work efficiently.

Definition of Enzymes

Enzymes are proteins (and some RNA molecules) that speed up biochemical reactions in living organisms without being consumed in the process. They lower the activation energy required for reactions to occur, making them happen faster.

Properties of Enzymes

• Highly specific: Each enzyme acts on a particular substrate.
• Efficient catalysts: Increase reaction speed millions of times.
• Required in small amounts: A little enzyme can catalyze many reactions.
• Work under mild conditions: Physiological temperature (37°C) and pH.
• Affected by pH and temperature: Extremes can denature enzymes.
• Can be regulated: Activated or inhibited when needed.

IUB and MB Classification of Enzymes

IUB (International Union of Biochemistry) Classification

Enzymes are classified into six major groups based on the type of reaction they catalyze:

1. Oxidoreductases: Catalyze oxidation–reduction reactions (e.g., dehydrogenases).
2. Transferases: Transfer functional groups (e.g., transaminases).
3. Hydrolases: Break bonds using water (e.g., lipases, proteases).
4. Lyases: Add or remove groups without hydrolysis (e.g., decarboxylases).
5. Isomerases: Rearrange molecules (e.g., isomerases).
6. Ligases: Join two molecules using ATP (e.g., DNA ligase).

MB (Michaelis–Menten / Biological) Classification

Based on substrate or biological role:

• Proteolytic enzymes: Trypsin, pepsin.
• Digestive enzymes: Amylase, lipase.
• Carbohydrate enzymes: Sucrase, maltase.
• Nucleases: DNase, RNase.

Factors Affecting Enzyme Activity

1. Temperature

Increases activity up to an optimum (around 37°C). Very high temperatures denature the enzyme.

2. pH

Each enzyme has an optimum pH (e.g., pepsin works best at pH 2, trypsin at pH 8). Extreme pH destroys enzyme activity.

3. Substrate Concentration

Activity increases with substrate concentration until the enzyme becomes saturated (reaches Vmax).

4. Enzyme Concentration

Higher enzyme levels increase reaction rate if substrate is available.

5. Activators

Metal ions like Mg²⁺, Zn²⁺ enhance enzyme function.

6. Inhibitors

Certain chemicals reduce enzyme activity (explained below).

Mechanism of Enzyme Action

The enzyme works by forming a temporary complex with its substrate.

1. Lock and Key Model

The enzyme’s active site fits the substrate exactly like a key fits a lock.

2. Induced Fit Model

The active site adjusts its shape slightly when the substrate binds, improving fit and increasing reaction efficiency. This is the more accepted model.

Steps in enzyme action:

1. Substrate binds to enzyme → forms enzyme–substrate complex.
2. The enzyme converts substrate into product.
3. Product is released and enzyme remains unchanged.

Enzyme Inhibitors

Enzyme inhibitors slow down or stop enzyme activity. They may be reversible or irreversible.

1. Competitive Inhibition

Inhibitor resembles the substrate and competes for the active site. Increasing substrate reduces inhibition.
Example: Sulfonamides inhibit bacterial folic acid synthesis.

2. Non-competitive Inhibition

Inhibitor binds to another site (not the active site) and changes enzyme shape.
Example: Heavy metals like mercury inhibit enzymes.

3. Uncompetitive Inhibition

Inhibitor binds only to the enzyme–substrate complex, reducing activity.

4. Irreversible Inhibition

Inhibitor permanently inactivates the enzyme.
Example: Nerve gases inhibit acetylcholinesterase.

Therapeutic and Pharmaceutical Importance of Enzymes

1. Therapeutic Uses

• Digestive enzymes: Amylase, lipase, protease for indigestion and pancreatic insufficiency.
• Fibrinolytic enzymes: Streptokinase to dissolve blood clots.
• Anti-inflammatory enzymes: Trypsin, chymotrypsin reduce swelling.
• Urokinase and tPA: Used in heart attack and stroke management.

2. Pharmaceutical Uses

• Enzymes in drug formulation: Used in manufacturing syrups, injections and diagnostic kits.
• Analytical enzymes: Glucose oxidase in glucose-monitoring devices.
• Biotechnological applications: Enzymes used in recombinant DNA technology.