Lyase
Encyclopedia
In biochemistry
, a lyase is an enzyme
that catalyzes the breaking of various chemical bond
s by means other than hydrolysis
and oxidation, often forming a new double bond
or a new ring structure. 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.
, aldolase
, etc. When the reverse reaction is more important, synthase
may be used in the name.
classification of enzymes. Lyases can be further classified into seven subclasses:
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
, a lyase is an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that catalyzes the breaking of various chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
s by means other than hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
and oxidation, often forming a new double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
or a new ring structure. For example, an enzyme that catalyzed this reaction would be a lyase:
- ATPAdenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
→ cAMPCyclic adenosine monophosphateCyclic adenosine monophosphate is a second messenger important in many biological processes...
+ PPi
Lyases differ from other enzymes in that they require only one substrate
Substrate (biochemistry)
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...
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, dehydrataseDehydratase
Dehydratase is an enzyme that catalyzes the removal of oxygen and hydrogen from organic compounds in the form of water. This process is also known as dehydration.There are four classes of dehydratases:...
, aldolase
Aldolase
Aldolase A is an enzyme that catalyses a reverse aldol reaction: The substrate, fructose 1,6-bisphosphate is broken down into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate . This reaction is a part of glycolysis. Three aldolase isozymes , encoded by three different genes, are...
, etc. When the reverse reaction is more important, synthase
Synthase
In biochemistry, a synthase is an enzyme that catalyses a synthesis process.Following the EC number classification, they belong to the group of ligases, with lyases catalysing the reverse reaction....
may be used in the name.
Classification
Lyases are classified as EC 4 in the EC numberEC number
The Enzyme Commission number is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze....
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 dehydrataseDehydrataseDehydratase is an enzyme that catalyzes the removal of oxygen and hydrogen from organic compounds in the form of water. This process is also known as dehydration.There are four classes of dehydratases:...
s - 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 adenylate cyclaseAdenylate cyclaseAdenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
and guanylate cyclaseGuanylate cyclase-Reaction:Guanylate cyclase catalyzes the reaction of guanosine triphosphate to 3',5'-cyclic guanosine monophosphate and pyrophosphate:-Types:... - EC 4.99 includes other lyases, such as ferrochelataseFerrochelataseFerrochelatase is an enzyme that catalyses the terminal step in the biosynthesis of heme, converting protoporphyrin IX into heme. It catalyses the reaction:A ferrochelatase enzyme consists of 497 amino acid residues with a m.w...
See also
- List of EC numbers of enzymes belonging to category EC 4