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. The reverse reaction is also possible (called a "Michael addition"). 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 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:
Membrane-associated lyases
Some lyases associate with biological membranes as peripheral membrane proteins or anchored through a single transmembrane helix.[1]
See also
References
- ^ Superfamilies of single-pass transmembrane lyases in Membranome database
- EC 4 Introduction from the Department of Chemistry at Queen Mary, University of London