Ligases

(or synthetases), a class of enzymes that catalyze the joining together of two molecules. They play an important role in the most significant anabolic processes—the biosynthesis of proteins, fats, and carbohydrates. Reactions catalyzed by ligases take place at the expense of energy released during the breakdown of adenosine triphosphate (ATP) or a similar triphosphate. The term “ligase” is also applied to synthesizing enzymes that act without the participation of nucleoside triphosphates.