Enzyme Classes and Co-enzymes

Major Classes of Enzymes

1. Oxido-reductases

   • Catalyze oxidation-reduction reactions
   • Example: Alcohol dehydrogenase
     • NAD+ as oxidizing agent (reduced to NADH)

2. Transferases

   • Transfer functional groups from one molecule to another
   • Example: Hexokinase
     • Transfers phosphate from ATP to glucose

3. Hydrolases

   • Catalyze hydrolytic cleavage
   • Example: Carboxypeptidase A
     • Cleaves polypeptides by breaking peptide bonds

4. Lyases

   • Add or remove groups to form double bonds
   • Example: Pyruvate decarboxylase
     • Removes CO2 from pyruvate to form acetaldehyde

5. Isomerases

   • Catalyze intermolecular rearrangements
   • Example: Malate isomerase
     • Converts malate (cis) to fumarate (trans)

6. Ligases

   • Join two molecules together
   • Example: Pyruvate carboxylase
     • Adds CO2 to pyruvate

Important Enzyme Nomenclature

• Enzymes are often named after their substrates and the type of reaction they catalyze.

Co-enzymes and Apoenzymes

• Co-enzyme: Non-protein molecule required by an enzyme to function
  • Associated with the active site
  • If present, enzyme is called a holoenzyme
  • If absent, enzyme is called an apoenzyme

Types of Co-enzymes

1. Organic Co-enzymes (Vitamins)

   • Examples: Thiamine, Riboflavin, Niacin, Biotin

2. Inorganic Co-enzymes (Minerals)

   • Examples: Mg2+, Fe2+, Zn2+, Mn2+

Role of Inorganic Co-enzymes

• Example: Zinc in Carboxypeptidase A
  • Activates water molecules, making oxygen more nucleophilic
  • Water acts as a nucleophile, attacking the peptide bond

Vitamins as Co-enzymes

• Vital for metabolism and energy extraction from food