Lyase

Lyase is a class of enzymes that catalyze the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. The reverse reaction can also often be performed. For example, an enzyme that catalyzed this reaction would be a lyase:

ATP → cAMP + PPi

Lyases differ from other enzymes in that they require only one substrate for the reaction in one direction, but two for the reverse reaction.

Classification

Lyases are classified as EC 4 in the EC number classification of enzymes. Lyases can be further classified into seven subclasses:

• EC 4.1 includes enzymes that cleave carbon-carbon bonds, such as decarboxylases, aldolases, and dehydratases.
• EC 4.2 includes enzymes that cleave carbon-oxygen bonds, such as dehydratases.
• EC 4.3 includes enzymes that cleave carbon-nitrogen bonds.
• EC 4.4 includes enzymes that cleave carbon-sulfur bonds.
• EC 4.5 includes enzymes that cleave carbon-halide bonds.
• EC 4.6 includes enzymes that cleave phosphorus-oxygen bonds.
• EC 4.99 includes other lyases.

Examples

Some of the enzymes classified as lyases include:

• Adenylyl cyclase
• ATP citrate lyase
• ATP: corrinoid adenosyltransferase
• Carbamoyl phosphate synthetase
• Cystathionine beta synthase
• Fructose-1,6-bisphosphatase
• Fumarase
• Histidine ammonia-lyase
• Isocitrate lyase
• Methylmalonyl-CoA mutase
• Pectin lyase
• Phosphoenolpyruvate carboxykinase
• Pyruvate decarboxylase
• Succinate dehydrogenase

See also

• Hydrolase
• Isomerase
• Ligase
• Oxidoreductase
• Transferase

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