Lyase
In
Michael reaction
). For example, an enzyme that catalyzed this reaction would be a lyase:
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
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:
- 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
- guanylyl cyclase
- EC 4.99 includes other lyases, such as ferrochelatase
Membrane-associated lyases
Some lyases associate with
transmembrane helix.[2]
See also
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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