Shikimic acid pathway

Pharmacognosy and phytochemistry-II, Semester V, Unit-I, Introduction of Shikimic acid pathway, Shikimic acid pathway/ role of shikimic acid pathway

1. SEMESTER V PHARMACOGNOSY AND PHYTOCHEMISTRY- II UNIT- I BASIC METABOLIC PATHWAY (Part-II) SHIKIMIC ACID PATHWAY Presented by: Miss. Pooja D. Bhandare Assistant professor Kandhar college of Pharmacy, nanded

2. SHIKIMIC ACID PATHWAY Introduction of Shikimic Acid Shikimic Acid is also know as Shikimate is its anionic form. Structurally it is a cyclohexane, a cyclitol and a cyclohexane carboxylic acid. It is an important biochemical metabolite in plants and micro-organisms. Its name derived from a Japanese plant Shikimi ( Illium anisatum ). Shikimic acid is first isolated from this plant in 1885 by Johan Fredric Eykman . Some hydrolysable tannins produced Shikimic acid as a glycoside part.

3. Shikimic acid pathway is utilized by bacteria, fungi, algae, parasites and plants for the biosynthesis of aromatic amino acid like phenylalanine, tyrosin and tryptophan. This pathway is not found in animals. Animals can synthesize tyrosine from phenylalanine and therefore it is not an essential amino acid except for individuals who unable to hydroxylate phenylalanine to tyrosine .

4. Shikimic acid pathway The Shikimic acid pathway is related to the metabolism of carbohydrate and aromatic amino acid. The pathway consist of seven steps, starting with the condensation of phosphoenolpyruvate and erythrose-4-phosphate. The condensation and cyclization lead to formation of shikimic acid and end with synthesis of chorismic acid.

5. Active form of these co-enzyme A ( CoA) can access the main classes of phenolic compounds, quoting some transformation to acids of benzoic acid series (gallic, protocatechuic, etc.) by ɮ- oxidation. Gallic acid itself, in combination with simple sugar, leads to the hydrolysable tannins (gallic and ellagic tannins), or, after the addition of molecule of phosphoenolpyruvate and additional series of intermediate stages, followed by amination, give rise to aromatic amino acids tyrosine and phenylalanine, the starting point of the phenylpropanoid pathway.

6. DHQ is dehydrated to 3- dehydroshikimic acid with the help of enzyme 3-dehydroquinate dehydratase. Further, 3- dehydroshikimic acid is formed is then reduced to Shikimic acid in the presence of enzymes Shikimate dehydrogenase, Which utilizes Nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor .

7. Shikimic acid also gets converted to Shikimic acid 3-phosphate in the presence of enzyme Shikimate kinase, an enzyme which catalyzes the ATP dependant phosphorylation. Shikimic acid 3-phosphate is then combine with phosphoenol pyruvate to 5-enolpyruvyl Shikimate-3-phosphate in the presence of enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) Synthase. Finally, 5-enolpyruvyl Shikimate-3-phosphate is get converted to Chrosimate in the presence of enzyme Chrosimate Synthase Shikimic acid 3-phosphate Chrosimate

8. Prephenic acid is then synthesized by Claisen rearrangement of Chrosimate with the enzyme chrosimate mutase. Prephenate is oxidatively decarboxylated with retention of hydroxyl group with the help of enzyme Prephenate dehydrogenase to produce p-hydroxy phenylpyruvate. This p-hydroxy phenylpyruvate is then transaminated using glutamate as a source of nitrogen precursor and produces tyrosine and α -ketoglutarate .

9. ROLE OF SHIKIMIC ACID PATHWAY Shikimic acid is the starting point in the biosynthesis of many phenolic compounds. Through Shikimic Acid Pathway phenylalanine and tyrosine are obtained which act as a precursor for the biosynthesis of phenypropanoids . The phenylpropanoids are then used to produce flavonoids, coumarins, lignin and tannins. Shikimic acid pathway is also helpful in Gallic acid biosynthesis Gallic acid is formed 3-dehyroshikimate in the presence of enzyme Shikimate dehydrogenase and produce 3,5-didehydroshikimate which rearranges and give Gallic acid. Shikimic acid pathway also involved in the biosynthesis of other compounds like Indole, Indole derivatives and aromatic amino acid derivatives, many alkaloids and other metabolic metabolites.