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In enzymology, a 3-phosphoshikimate 1-carboxyvinyltransferase is an enzyme that catalyzes the chemical reaction. It is otherwise known as EPSP synthase.


 * phosphoenolpyruvate + 3-phosphoshikimate $$\rightleftharpoons$$ phosphate + 5-O-(1-carboxyvinyl)-3-phosphoshikimate

Thus, the two substrates of this enzyme are phosphoenolpyruvate and 3-phosphoshikimate, whereas its two products are phosphate and 5-O-(1-carboxyvinyl)-3-phosphoshikimate.

EPSP Synthase
The enzyme belongs to the family of transferases, to be specific those transferring aryl or alkyl groups other than methyl groups. The systematic name of this enzyme class is phosphoenolpyruvate:3-phosphoshikimate 5-O-(1-carboxyvinyl)-transferase. Other names in common use include 5-enolpyruvylshikimate-3-phosphate synthase, 3-enolpyruvylshikimate 5-phosphate synthase, 3-enolpyruvylshikimic acid-5-phosphate synthetase, 5'-enolpyruvylshikimate-3-phosphate synthase, 5-enolpyruvyl-3-phosphoshikimate synthase, 5-enolpyruvylshikimate-3-phosphate synthetase, 5-enolpyruvylshikimate-3-phosphoric acid synthase, enolpyruvylshikimate phosphate synthase, and EPSP synthase. The enzyme participates in biosynthesis of the aromatic amino acids phenylalanine, tyrosine and tryptophan. The enzyme is a target for herbicides as these amino acids are only synthesized in plants and microorganisms. Glyphosate acts as a competive inhibitor for phosphoenolpyruvate and is used as a broad-spectrum systemic herbicide.

Shikimate pathway
The Shikimate pathway is a seven step metabolic route for the biosythesis of the benzene ring, which is a structure found in aromatic compounds. The pathway is not involved in the synthesis of all aromatic compounds; it mainly manufactures phenylalanine, tyrosine, and tryptophan. Though all aromatic compounds contain a benzene ring, some compounds can be synthesized through other pathways. The products of the pathway, Phe and Trp, are essential amino acids for humans; however, this pathway is not found in humans, so these compounds must be taken in through diet. Tyr can be synthesized from Phe.

Structural Analysis
EPSP synthase is a monomeric enzyme. It is composed of two domains, which are joined by protein strands. This strand acts as a hinge, and can bring the two protein domains closer together. When a substrate binds to the enzyme, ligand bonding causes the two parts of the enzyme to clamp down around the substrate in the active site.

Process


EPSP synthase catalyzes the reaction which converts shikimate-3-phosphate plus phosphoenolpyruvate to 5-enolpyruvylshikimate-3-phosphate(EPSP).

Roundup
Roundup, is a chemical herbicide which inhibits plant growth by inhbiting the Shikimate pathway. It focuses on the step catalyzed by EPSP synthase, the step in which shikimate-3-phosphate and phosphoenolpyruvate are converted to EPSP. The chemical in roundup, glyphosate, is a competitive inhibitor of phosphoenolpyruvate; this means that glyphosate will bind with shikimate-3-phosphate instead of phosphoenolpyruvate, creating a shikimate-3-phosphate/glyphosate complex. This complex is similar to the transition state of EPSP sythase. This binding leads to the inhibition of the conversion, and consequently the inhibition of the entire pathway. Since plants need the Shikimate pathway to produce aromatic amino acids, this kills the plant. This also means that Roundup is generally harmless to humans, since we do not produce Phe, Trp, and Tyr using the Shikimate pathway.