Lyase

Lyases are enzymes that catalyze bond cleavage or formation by mechanisms other than hydrolysis or oxidation. They typically effect eliminations or additions that generate a double bond or a new ring, and may release small molecules such as CO2, H2O, or ammonia in the process. The reaction often proceeds without a net redox change.

Classification and examples: The Enzyme Commission (EC) classifies lyases as EC 4. The major subdivisions are based on the type of bond cleaved: carbon–carbon lyases (4.1), carbon–oxygen lyases (4.2), carbon–nitrogen lyases (4.3), and carbon–sulfur lyases (4.4). Aldolases (EC 4.1.2.x) cleave carbon–carbon bonds, decarboxylases (EC 4.1.1.x) remove CO2, and fumarase (EC 4.2.1.2) hydrates or dehydrates substrates across carbon–oxygen bonds.

Mechanism and cofactors: Many lyases employ cofactors such as pyridoxal phosphate (PLP), metal ions (for example iron-sulfur clusters), or coenzymes to stabilize reaction intermediates. Some lyases catalyze reversible reactions and function in both directions depending on substrate concentration and cellular conditions.

Role in biology: Lyases participate in a wide range of metabolic pathways, including glycolysis, gluconeogenesis, amino acid biosynthesis, and carbohydrate metabolism. They enable rapid formation of reactive intermediates and structural versatility in metabolism. The term lyase is one of several EC classes used to describe enzyme-catalyzed transformations, highlighting the diversity of chemical strategies in living systems.

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