Oxidoreductases: Enzymes involved in oxidation-reduction reactions. Transferases: Enzymes that catalyse the transfer of functional groups. Hydrolases: Enzymes that bring about hydrolysis of various compounds. Lyases: Enzymes specialized in the addition or removal of water, ammonia, CO2 etc. Isomerases: Enzymes involved in all the isomerization reactions. Ligases: Enzymes catalysing the synthetic reactions (Greek: ligate-to bind) where two molecules are joined together and ATP is used.Reference - satyanarayana Pg-87