The

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

anthranilate synthase ()

catalyzes Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

the

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...

:chorismate + L-glutamine

\rightleftharpoons

anthranilate + pyruvate + L-glutamate

Function

Anthranilate synthase creates anthranilate, an important intermediate in the biosynthesis of

indole Indole is an aromatic heterocyclic organic compound with the formula C8 H7 N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environme ...

, and by extension, the amino acid

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromati ...

. Tryptophan can then be metabolized further into serotonin,

melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrat ...

, or various auxins.

Reaction

Anthranilate synthase catalyzes the change from chorismate to anthranilate. As its other substrate, it can use either glutamine or

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...

. During the reaction, both a hydroxyl group and an enolpyruvyl group are removed from the

aromatic ring In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satu ...

. The enolpyruvyl group gains a proton to form

pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...

. It has been shown that the proton comes from the surrounding water and not from an intramolecular shift of a hydrogen atom on the substrates. The

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

of glutamine (or ammonia itself) attacks chorismate in position 2, which leads to the elimination of enolpyruvyl group from position 3. In the process, an aromatic ring is re-formed. :

Structure and assembly

The complex is made up of α and β subunits. Gel filtration experiments reveal that the complex occurs as an α₂β₂ tetramer under native conditions, and as an αβ dimer under high salt concentrations. The αβ dimers interact through the α subunits to form the complex. The subunits of anthranilate synthase are encoded by the trpE and trpD genes in ''E. coli'', both of which appear in the trp operon. In

Enterobacteriaceae Enterobacteriaceae is a large family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but on ...

, this enzyme exists in the form of an aggregate with anthranilate phosphoribosyltransferase. If these two enzymes are not clustered, the complex is unable to use glutamine as a substrate and can only use ammonia.

Homologs

Paralogs

Nomenclature

This enzyme belongs to the family of

lyase In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bond A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bon ...

s, to be specific the oxo-acid-lyases, which cleave carbon-carbon bonds. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is chorismate pyruvate-lyase (amino-accepting; anthranilate-forming). Other names in common use include anthranilate synthetase, chorismate lyase, and chorismate pyruvate-lyase (amino-accepting). This enzyme participates in phenylalanine, tyrosine and tryptophan biosynthesis and two-component system - general.

Structural studies

As of late 2007, five structures have been solved for this class of enzymes, with PDB accession codes , , , , and .

Application

References

* * * * * EC 4.1.3 Enzymes of known structure Anthranilates {{4.1-enzyme-stub