Ligases: These enzymes catalyze the covalent bonding of two substrates to form a large molecule. They catalyze the joining of C–O, C–S, S–N, P–O, etc., bonds by using the energy of ATP. They are also called molecular glue or stickers.
Example: DNA ligase. Two DNA molecules are joined together by a phosphodiester bond in the presence of DNA ligases. The enzymes cannot be utilised for the blunt ends of the fragments of DNA. The bond nature is covalent because of the involvement of electron exchange.