Shikimate pathway

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The shikimate pathway (shikimic acid pathway) is a seven step metabolic route used by bacteria, fungi, algae, some protozoan parasites and plants for the biosynthesis of folates and aromatic amino acids (phenylalanine, tyrosine, and tryptophan). This pathway is not found in animals, which require these amino acids, hence the products of this pathway represent essential amino acids that must be obtained from bacteria or plants (or animals which eat bacteria or plants) in the animal's diet.

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, a substrate for the three aromatic amino acids. The fifth enzyme involved is the shikimate kinase, an enzyme that catalyzes the ATP-dependent phosphorylation of shikimate 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.

Chorismate pathway 1.png

Then 5-enolpyruvylshikimate-3-phosphate is transformed into chorismate by a chorismate synthase.

Chorismate pathway 2.png

Prephenic acid is then synthesized by a Claisen rearrangement of chorismate by Chorismate mutase.[2][3]

Prephenate biosynthesis.png

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.

Tyrosine biosynthesis.svg

References[edit]

  1. ^ Herrmann, K. M.; Weaver, L. M. (1999). "The Shikimate Pathway". Annual Review of Plant Physiology and Plant Molecular Biology. 50: 473–503. doi:10.1146/annurev.arplant.50.1.473. PMID 15012217. 
  2. ^ Helmut Goerisch (1978). "On the mechanism of the chorismate mutase reaction". Biochemistry. 17 (18): 3700. doi:10.1021/bi00611a004. 
  3. ^ Peter Kast, Yadu B. Tewari, Olaf Wiest, Donald Hilvert, Kendall N. Houk, and Robert N. Goldberg (1997). "Thermodynamics of the Conversion of Chorismate to Prephenate: Experimental Results and Theoretical Predictions". J. Phys. Chem. B. 101 (50): 10976–10982. doi:10.1021/jp972501l. 

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