🧪 1. Classification and Naming of Enzymes

To avoid confusion caused by multiple common names, enzymes are systematically classified and named by the International Union of Biochemistry and Molecular Biology (IUBMB).

Each enzyme is given an EC number (Enzyme Commission number) based on the type of reaction it catalyzes.

There are six major classes of enzymes:

EC Class Enzyme Class What They Do (Easy Meaning) Common Examples
1 Oxidoreductases Carry out oxidation–reduction reactions (transfer of electrons / H / O) Dehydrogenase, Oxidase, Catalase
2 Transferases Transfer functional groups (–CH₃, –NH₂, –PO₄) Transaminase, Kinase
3 Hydrolases Break bonds using water (hydrolysis) Amylase, Protease, Lipase
4 Lyases Break bonds without water or ATP, often forming double bonds Decarboxylase, Aldolase
5 Isomerases Convert a molecule into its isomer Glucose-6-P isomerase
6 Ligases Join two molecules using ATP energy DNA ligase, Synthetase

⭐ Key Exam Point: Hydrolase uses water, Lyase does NOT use water.

🧩 2. Co-factors – Helpers of Enzymes

Many enzymes cannot work alone. They need a non-protein helper called a co-factor.

  • Apoenzyme: Protein part alone → inactive
  • Co-factor: Non-protein helper
  • Holoenzyme: Apoenzyme + Co-factor → active enzyme

🔗 Types of Co-factors

1️⃣ Prosthetic Groups

  • Organic molecules
  • Tightly and permanently bound to enzyme
  • Often covalently attached

Example:

  • Heme in catalase and peroxidase

🧠 Memory Line: Prosthetic = Permanent partner

2️⃣ Co-enzymes

  • Organic molecules
  • Loosely bound (bind → help → leave)
  • Mostly derived from vitamins

Examples:

  • NAD / NADP → from Vitamin B₃ (Niacin)
  • FAD → from Vitamin B₂ (Riboflavin)

Role: Electron / hydrogen carriers

⭐ NEET Favorite: Vitamin deficiency → enzyme malfunction

3️⃣ Metal Ion Co-factors

  • Inorganic ions
  • Help in substrate binding or enzyme activation

Examples:

  • Zn²⁺ → Carboxypeptidase
  • Mg²⁺ → Kinases
  • Fe²⁺ / Fe³⁺ → Cytochromes

🧠 Tip: Metal ions stabilize negative charges in reactions

📌 Why Co-factors Are Important

  • Increase enzyme efficiency
  • Enable reactions not possible by protein alone
  • Link metabolism to vitamins and minerals

🧠 Memory Capsules – Enzyme Classification & Co-factors

6 Enzyme classes (O-T-H-L-I-L)

  • Oxidoreductase
  • Transferase
  • Hydrolase
  • Lyase
  • Isomerase
  • Ligase

Important Points

  • Hydrolase = water, Lyase = no water
  • Apoenzyme → inactive protein
  • Holoenzyme = Apoenzyme + Co-factor
  • Prosthetic group → tightly bound
  • Co-enzyme → loosely bound (vitamin-derived)
  • Metal ions → Zn²⁺, Mg²⁺, Fe²⁺

🔁 Mnemonic: “Old Teachers Help Lazy Intelligent Learners”

💡 Questions and Answers

Q1. How are enzymes classified?

A1. Enzymes are classified by IUBMB into six classes based on the type of reaction they catalyze.

Key Points:

  • Reaction-based classification
  • Six major classes

Q2. What is a holoenzyme?

A2. A holoenzyme is the active form of an enzyme, consisting of the apoenzyme (protein part) plus a co-factor.

Key Points:

  • Apoenzyme alone is inactive
  • Co-factor is essential

Q3. Differentiate between prosthetic group and co-enzyme.

A3. A prosthetic group is tightly bound to the enzyme, while a co-enzyme is loosely bound and often vitamin-derived.

Key Points:

  • Binding strength
  • Vitamin origin of co-enzymes

Q4. Give one example of a metal ion co-factor.

A4. Zinc (Zn²⁺) is required for the enzyme carboxypeptidase.

Key Points:

  • Metal ion helps catalysis

Q5. Which class of enzymes joins two molecules using ATP?

A5. Ligases (EC-6).

Key Points:

  • ATP dependent
  • Bond formation