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. 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:

  • 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.[1]

gollark: Better *how*?
gollark: Oh, flash storage, that is a huge one.
gollark: ... which we *have had*, modern computers are better than 30-year-old ones.
gollark: So, say, OLEDs, capacitative touchscreens (okay, I'm not sure how old those are), much faster RAM and new RAM technologies, laptops which you can actually carry, and transistors at the scale of tens of nanometres are not "new technologies"?
gollark: Laptops now are very different to ye olden laptops, touchscreens... are generally better now, I guess, LCDs can go to crazy resolutions and refresh rates and are being replaced by OLEDs in some areas, "microprocessors" is so broad and ignores the huge amount of advancement there.

See also

References
  1. Superfamilies of single-pass transmembrane lyases in Membranome database
  • EC 4 Introduction from the Department of Chemistry at Queen Mary, University of London


This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.