The shikimate pathway (

shikimic acid Shikimic acid, more commonly known as its anionic form shikimate, is a cyclohexene, a cyclitol and a cyclohexanecarboxylic acid. It is an important biochemical metabolite in plants and microorganisms. Its name comes from the Japanese flower ''sh ...

pathway) is a seven-step

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...

used by

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

, archaea,

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

alga Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from u ...

e, some protozoans, and

plant Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...

s for the biosynthesis of

folate Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...

s and aromatic amino acids (

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 ...

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...

, and

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

). This pathway is not found in animal cells. The seven enzymes involved in the shikimate pathway are DAHP synthase,

3-dehydroquinate synthase The enzyme 3-dehydroquinate synthase (EC 4.2.3.4) catalyzes the chemical reaction : 3-deoxy-D-''arabino''-hept-2-ulosonate 7-phosphate \rightleftharpoons 3-dehydroquinate + phosphate The protein uses NAD+ to catalyze the reaction. This react ...

3-dehydroquinate dehydratase The enzyme 3-dehydroquinate dehydratase () catalyzes the chemical reaction :3-dehydroquinate \rightleftharpoons 3-dehydroshikimate + H2O This enzyme belongs to the family of lyases, specifically the hydro-lyases, which cleave carbon-oxygen b ...

, shikimate dehydrogenase, shikimate kinase, EPSP synthase, and chorismate synthase. The pathway starts with two

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

s, phosphoenol pyruvate and erythrose-4-phosphate, and ends with chorismate, a substrate for the three aromatic amino acids. The fifth

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 ...

involved is the shikimate kinase, an enzyme that catalyzes the

ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals, men's professional tennis governing body * American Technical Publishers, employee-owned publishing company * ', a Danish pension * Armenia Tree Project, non ...

-dependent

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, ...

of shikimate to form shikimate 3-phosphate (shown in the figure below). Shikimate 3-phosphate is then coupled with phosphoenol pyruvate to give

5-enolpyruvylshikimate-3-phosphate 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase is an enzyme produced by plants and microorganisms. EPSPS catalyzes the chemical reaction: : phosphoenolpyruvate (PEP) + 3-phospho shikimate (S3P) phosphate + 5-enolpyruvylshikimate-3-phospha ...

via the enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase. Glycine phosphonate, more commonly known as

Roundup A roundup is a systematic gathering together of people or things. Roundup, Round Up or Round-up may also refer to: Agriculture * A muster (livestock) (AU/NZ) or a roundup (US/CA) is the process of gathering livestock. * Roundup (herbicide), a M ...

, is a competitive inhibitor of EPSP synthase, acting as a transition state analog that binds more tightly to the EPSPS-S3P complex than PEP and inhibits the shikimate pathway. : Chorismate pathway 1

Then 5-enolpyruvylshikimate-3-phosphate is transformed into chorismate by a chorismate synthase. : Chorismate pathway 2

Prephenic acid is then synthesized by a

Claisen rearrangement The Claisen rearrangement is a powerful carbon–carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl vinyl ether will initiate a ,3sigmatropic rearrangement to give a γ,δ-unsaturated carbonyl, ...

of chorismate by

chorismate mutase In enzymology, chorismate mutase () is an enzyme that catalyzes the chemical reaction for the conversion of chorismate to prephenate in the pathway to the production of phenylalanine and tyrosine, also known as the shikimate pathway. Hence, this ...

. :

Prephenate is oxidatively decarboxylated with retention of the

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

group to give ''p''-hydroxyphenylpyruvate, which is transaminated using

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...

as the nitrogen source to give

and α-ketoglutarate. : Tyrosine biosynthesis

References

Bibliography

* * * * {{MetabolismMap Metabolic pathways