Lyases

In biochemistry, a lyase is an enzyme that catalyzes the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. For example, an enzyme that catalyzed this reaction would be a lyase:


 * ATP &rarr; cAMP + PPi

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

Nomenclature
Systematic names are formed as "substrate group lyase." Common names include decarboxylase, dehydratase, aldolase, etc. When the reverse reaction is more important, synthase may be used in the name.

Classification
Lysases are classified as EC 4 in the EC number classification of enzymes. Lyases can be further classified into seven subclasses:
 * EC 4.1 includes lyases that cleave carbon-carbon bonds, such as decarboxylases (EC 4.1.1), aldehyde lyases (EC 4.1.2), oxo acid lyases(EC 4.1.3) and others (EC 4.1.99)
 * EC 4.2 includes lyases that cleave carbon-oxygen bonds, such as dehydratases
 * EC 4.3 includes lyases that cleave carbon-nitrogen bonds
 * EC 4.4 includes lyases that cleave carbon-sulfur bonds
 * EC 4.5 includes lyases that cleave carbon-halide bonds
 * EC 4.6 includes lyases that cleave phosphorus-oxygen bonds, such as adenylate cyclase and guanylate cyclase
 * EC 4.99 includes other lyases, such as ferrochelatase