Lyase

In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bonds by means other than hydrolysis (a substitution reaction) and oxidation, often forming a new double bond or a new ring structure.^[1] The reverse reaction is also possible (called a Michael reaction). For example, an enzyme that catalyzed this reaction would be a lyase:

ATP → cAMP + PP_i

Lyases differ from other enzymes in that they require only 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 product is more important, synthase may be used in the name, e.g. phosphosulfolactate synthase (EC 4.4.1.19, Michael addition of sulfite to phosphoenolpyruvate). A combination of both an elimination and a Michael addition is seen in O-succinylhomoserine (thiol)-lyase (MetY or MetZ) which catalyses first the γ-elimination of O-succinylhomoserine (with succinate as a leaving group) and then the addition of sulfide to the vinyl intermediate, this reaction was first classified as a lyase (EC 4.2.99.9), but was then reclassified as a transferase (EC 2.5.1.48).

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 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 adenylyl cyclase and guanylyl cyclase
EC 4.99 includes other lyases, such as ferrochelatase

Membrane-associated lyases

Some lyases associate with biological membranes as peripheral membrane proteins or anchored through a single transmembrane helix.^[2]

References

^ "Lyase". www.uniprot.org.
^ Superfamilies of single-pass transmembrane lyases in Membranome database

EC 4 Introduction from the Department of Chemistry at Queen Mary, University of London

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[1] "Lyase". www.uniprot.org.

[2] Superfamilies of single-pass transmembrane lyases in Membranome database

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v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)

v t e Carbon–carbon lyases (EC 4.1)
4.1.1: Carboxy-lyases	Acetoacetate decarboxylase Adenosylmethionine decarboxylase Arginine decarboxylase Aromatic L-amino acid decarboxylase Glutamate decarboxylase Histidine decarboxylase Lysine decarboxylase Malonyl-CoA decarboxylase Ornithine decarboxylase Oxaloacetate decarboxylase Phosphoenolpyruvate carboxykinase Phosphoenolpyruvate carboxylase Phosphoribosylaminoimidazole carboxylase Pyrophosphomevalonate decarboxylase Pyruvate decarboxylase RuBisCO Uridine monophosphate synthetase/Orotidine 5'-phosphate decarboxylase Uroporphyrinogen III decarboxylase
4.1.2: Aldehyde-lyases	Fructose-bisphosphate aldolase Aldolase A Aldolase B Aldolase C 2-hydroxyphytanoyl-CoA lyase Threonine aldolase
4.1.3: Oxo-acid-lyases	Isocitrate lyase 3-hydroxy-3-methylglutaryl-CoA lyase
4.1.99: Other	Tryptophanase Photolyase CPD lyase Spore photoproduct lyase

v t e Carbon–oxygen lyases (EC 4.2) (primarily dehydratases)
4.2.1: Hydro-Lyases	Carbonic anhydrase Fumarase Aconitase Enolase Alpha Enolase 2 Enoyl-CoA hydratase/3-Hydroxyacyl ACP dehydrase Methylglutaconyl-CoA hydratase Tryptophan synthase Cystathionine beta synthase Porphobilinogen synthase 3-Isopropylmalate dehydratase Urocanase Uroporphyrinogen III synthase Nitrile hydratase
4.2.2: Acting on polysaccharides	Hyaluronate lyase Pectin lyase
4.2.3: Acting on phosphates	Threonine synthase
4.2.99: Other	Carboxymethyloxysuccinate lyase Hydroperoxide lyase

v t e Carbon–nitrogen lyases (EC 4.3)
4.3.1: ammonia-lyases	Histidine ammonia-lyase Formiminotransferase cyclodeaminase Serine dehydratase Phenylalanine ammonia-lyase
4.3.2: amidine-lyases	Argininosuccinate lyase Adenylosuccinate lyase

Nomenclature

Classification

Membrane-associated lyases

See also

References