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Phosphoenolpyruvate (PEP) condenses with erythrose 4-phosphate to form a 7-carbon compound,

Phosphoenolpyruvate (PEP) condenses with erythrose 4-phosphate to form a 7-carbon compound, 2-keto 3-deoxy arabinoheptulosonate, DAHP. DAHP cyclises to form 5-dehydroquinate. 5-dehydroquinate. Dehydration and reduction yield shikimate. Shikimate. Quinate. EPSPS.

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Phosphoenolpyruvate (PEP) condenses with erythrose 4-phosphate to form a 7-carbon compound,

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  1. Phosphoenolpyruvate (PEP) condenses with erythrose 4-phosphate to form a 7-carbon compound, 2-keto 3-deoxy arabinoheptulosonate, DAHP.

  2. DAHP cyclises to form 5-dehydroquinate. 5-dehydroquinate Dehydration and reduction yield shikimate. Shikimate Quinate

  3. EPSPS Glyphosate inhibits this enzyme in plants. Shikimate is phosphorylated and condensed with a molecule of phosphoenolpyruvate. Enolpyruvoyl shikimate 5-phosphate

  4. Elimination of the phosphate results in formation of chorismate. Chorismate

  5. Biosynthesis of PHE and TYR Chorismate mutase converts chorismate to prephenate.

  6. + CO2 Prephenate dehydratase forms the a-ketoacid precursor of PHE.

  7. Prephenate dehydrogenase forms the a-ketoacid precursor of TYR.

  8. TRP biosynthesis Chorismate is converted to anthranilate. GLN is the amino group donor. Anthranilate synthase produces NH3 by hydrolysing GLN. Addition of the NH3 to the ring results in elimination of water.

  9. Loss of a proton from C2 of the resulting intermediate leads to elimination of enolpyruvate. This reaction is favoured because it leads to formation of an aromatic ring, a highly stable product.

  10. Anthranilate reacts with PRPP to form phosphoribosyl anthranilate.

  11. The sugar ring opens. [Reaction is similar to PRPP ribose opening in HIS biosynthesis.] A complex reaction results in formation of indole glycerol phosphate.

  12. TRP synthase catalyses reaction of serine with indole glycerol phosphate to form TRP and glyceraldehyde 3-phosphate. + serine +glyceraldehyde 3-phosphate The carbon atoms of serine replace those of glycerol phosphate.

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