synthases

Synthases are enzymes that catalyze the formation of a product by bringing together two substrates or by forming a new bond within a molecule, typically through a condensation reaction. The term is historically associated with reactions that do not require the direct input of energy from ATP or another nucleotide triphosphate, and many synthases operate at a steady, equilibrium-driven pace in central metabolism.

The distinction between synthases and synthetases is historical and naming can be inconsistent. Synthetases are enzymes that catalyze ligation reactions in which bond formation is driven by the energy released from ATP or another nucleotide triphosphate. In practice, some enzymes named synthases can function without ATP, while others bearing the label synthetase explicitly use energy input. Because names reflect traditional classifications rather than strict energy requirements, the exact categorization can vary by context.

Representative examples of synthases include citrate synthase, which condenses acetyl-CoA and oxaloacetate to form citrate in the citric acid cycle, and malate synthase, which participates in the glyoxylate cycle by combining glyoxylate and acetyl-CoA to produce malate. These enzymes illustrate the role of synthases in constructing larger molecules from smaller precursors without direct ATP hydrolysis.

In summary, synthases are a broad class of enzymes that catalyze synthesis-oriented reactions, with nomenclature rooted in historical usage and often, but not always, independent of direct energy input. The terminology can overlap with other enzyme classes, reflecting advances in enzymology and pathway context.