The shikimate pathway (shikimic acid pathway) is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesisoffolates and aromatic amino acids (tryptophan, phenylalanine, and tyrosine). This pathway is not found in mammals.
The seven enzymes involved in the shikimate pathway are DAHP synthase, 3-dehydroquinate synthase, 3-dehydroquinate dehydratase, shikimate dehydrogenase, shikimate kinase, EPSP synthase, and chorismate synthase. The pathway starts with two substrates, phosphoenol pyruvate and erythrose-4-phosphate, and ends with chorismate (chrorismic acid), a substrate for the three aromatic amino acids. The fifth enzyme involved is the shikimate kinase, an enzyme that catalyzes the ATP-dependent phosphorylationofshikimate to form shikimate 3-phosphate (shown in the figure below).[1] Shikimate 3-phosphate is then coupled with phosphoenol pyruvate to give 5-enolpyruvylshikimate-3-phosphate via the enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase. Glyphosate, the herbicidal ingredient in Roundup, 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.
Then 5-enolpyruvylshikimate-3-phosphate is transformed into chorismate by a chorismate synthase.
Prephenic acid is then synthesized by a Claisen rearrangementofchorismatebychorismate mutase.[2][3]
Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give p-hydroxyphenylpyruvate, which is transaminated using glutamate as the nitrogen source to give tyrosine and α-ketoglutarate.
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Metabolism map
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Single lines: pathways common to most lifeforms. Double lines: pathways not in humans (occurs in e.g. plants, fungi, prokaryotes).  Orange nodes: carbohydrate metabolism.  Violet nodes: photosynthesis.  Red nodes: cellular respiration.  Pink nodes: cell signaling.  Blue nodes: amino acid metabolism.  Grey nodes: vitamin and cofactor metabolism.  Brown nodes: nucleotide and protein metabolism.  Green nodes: lipid metabolism.
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