Question

Long answer question.

How are enzymes classified? Mention an example of each class.

Answer 1

Enzymes are classified into six classes:

1. Oxidoreductases: These enzymes catalyze oxidation and reduction reactions by the transfer of hydrogen and/or oxygen.
   e.g. alcohol dehydrogenase
   \[\ce{Alcohol + NAD^+ ->[Alcohol][dehydroenase] Aldehyde + NADH2}\]
2. Transferases: These enzymes catalyse the transfer of certain groups between two molecules. e.g. glucokinase
   \[\ce{Glucose + ATP ->[Glucokinase] Glucose – 6 – Phosphate + ADP}\]
3. Hydrolases: These enzymes catalyze hydrolytic reactions. This class includes amylases, proteases, lipases etc. e.g. Sucrase
   \[\ce{Sucrose + water ->[Sucrase] Glucose + Fructose}\]
4. Lyases: These enzymes are involved in elimination reactions resulting in the removal of a group of atoms from the substrate molecule to leave a double bond. It includes aldolases, decarboxylases, and dehydratases, e.g. fumarate hydratase.
   \[\ce{Histidine ->[Histidine][deca rbox ylase]Histamine + CO2}\]
5. Isomerases: These enzymes catalyze structural rearrangements within a molecule. Their nomenclature is based on the type of isomerism. Thus, these enzymes are identified as racemases, epimerases, isomerases, mutases, e.g. xylose isomerase.
   \[\ce{Glucose – 6 – Phosphate ->[Isomerase] Fructose – 6 – Phosphate}\]
6. Ligases or Synthetases: These are the enzymes which catalyze the covalent linkage of the molecules utilizing the energy obtained from hydrolysis of an energy-rich compound like ATP, GTP e.g. glutathione synthetase, Pyruvate carboxylase.
   \[\ce{Pyruvate + CO2 + ATP ->[Pyruvate][ca rbox ylase] Oxaloacetate + ADP + Pi}\]