1. any of a class of enzymes that catalyze the linkage of two molecules, generally utilizing atp as the energy donor. also called synthetase.

1. any of a group of enzymes that catalyze the binding of two molecules; synthetase.

1. an enzyme which catalyzes creation of a covalent bond between two substrates, resulting in a larger product which is a combination of the two starting materials; especially, dna ligase, an enzyme which creates a phosphate bond between 5′ and 3′ ends of a dna chain, resulting in a longer chain of dna. dna ligase is important in normal biosynthesis of dna in the replication cycle of cells.