Inbiochemistry, alyase is anenzyme that catalyzes thebreaking (anelimination reaction) of variouschemical bonds by means other thanhydrolysis (asubstitution reaction) andoxidation, often forming a newdouble bond or a newring structure.[1] The reverse reaction is also possible (called aMichael reaction). For example, an enzyme that catalyzed this reaction would be a lyase:
Lyases differ from other enzymes in that they require only onesubstrate for the reaction in one direction, but two substrates for the reverse reaction.
Systematic names are formed as "substrate group-lyase." Common names includedecarboxylase,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).
Lyases are classified as EC 4 in theEC number classification of enzymes. Lyases can be further classified into seven subclasses:
Some lyases associate withbiological membranes asperipheral membrane proteins or anchored through a singletransmembrane helix.[2]
