Enzymes are classified according to their function and type of reaction in which they are taking part.
Four main classes of enzymes are :
(i) Oxidoreductases : These enzymes catalyze oxidation and reduction reactions, usually involving the transfer of hydrogen from one molecule to another.
S reduced + S’ oxidized ------S oxidized + S’ reduced
(ii) Transferases : These enzymes transfer a chemical group from one substrate to another but never hydrogen e.g. phosphotransferase catalyzes the transfer of a phosphate group from one molecule to another.
(iii) Hydrolases : These enzymes carry out hydrolysis reactions i.e., breakdown of large molecules by addition of water e.g. lipases breakdown lipids into fatty acids and glycerol.
(iv) Ligase or synthetase : These enzymes form bonds to join two molecules together, using energy supplied from the breakdown of ATP e.g. DNA ligase is used to repair breaks in DNA molecules.
