Types of Enzymes

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Points to Ponder for NEET-PG, FMGE & NEXT

• Enzymes are biological catalysts.
• Oxidoreductases remove hydrogen atoms or add oxygen atoms.
• Hydroxylases incorporate one atom of oxygen into a substrate.
• Transferases transfer a functional group from one molecule to another.
• Hydrolases break down molecules by adding water at a specific covalent bond.
• Lyases cleave c-c, c-n, or other covalent bonds without using water.
• Isomerases rearrange atoms within a molecule to create a different isomer.
• Ligases/synthetases join two molecules together using energy.

Enzymes

• Enzymes are biological catalysts that accelerate biochemical reactions.
• They are classified based on the type of chemical reaction they catalyze.

1. Oxidoreductases

• Function: Remove hydrogen atoms (dehydrogenation) or add oxygen atoms (oxidation)
• Subtypes:
  • Dehydrogenases: Remove hydrogen using electron acceptors like NAD⁺, NADP⁺, or FAD:
    • Examples: Pyruvate dehydrogenase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, succinate dehydrogenase.
  • Oxidases: Use molecular oxygen (O₂) as the hydrogen acceptor (e.g., respiratory burst During phagocytosis activates oxidase)
  • Hydroxylases (Monooxygenases): Incorporate one atom of oxygen into a substrate, often forming a hydroxyl group (OH). (e.g., Phenylalanine hydroxylase)
  • Dioxygenases: Incorporate both atoms of an O₂ molecule into the substrate.

2. Transferases

• Function: Transfer a functional group (e.g., methyl, phosphate) from one molecule (donor) to another (acceptor).
• Examples: Kinases (phosphotransferases), transketolase, transaldolase.

3. Hydrolases

• Function: Break down molecules by adding water (hydrolysis) at a specific covalent bond.
• Examples:
  • Proteases (Peptidases): Break down proteins into peptides and amino acids.
  • Esterases: Break down esters into alcohols and carboxylic acids.
  • Phospholipases: Break down phospholipids.
  • Amidases: Break down amides into carboxylic acids and ammonia.

4. Lyases

• Function: Cleave C-C, C-N, or other covalent bonds without using water. Often involve the creation of a double bond.
• Examples:
  • Decarboxylases: Remove carboxyl groups (CO₂) from molecules.
  • Hydratases: Add water to a molecule, forming a single bond.
  • Aldolases: Cleave fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
  • Dehydratases: Remove water from a molecule, forming a double bond.

5. Isomerases

• Function: Rearrange atoms within a molecule to create a different isomer (same chemical formula, different structure).
• Examples:
  • Epimerases: Convert one stereoisomer to another (e.g., glucose-6-phosphate isomerase).
  • Mutases: Move a functional group within a molecule (e.g., phosphoglycerate mutase).

6. Ligases (Synthetases)

• Function: Join two molecules together using energy from ATP to form a new covalent bond.
• Examples: Carboxylases (fix CO₂ into organic molecules).

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