Aromatic amino acids

Metabolism of aromatic amino acids , basic classifiaction of aminoacids

1. Basic concepts of Amino acid & Metabolism of aromatic amino acids Mrs.R.GLORIA JEMMI CHRISTOBEL ASSISTANT PROFESSOR DEPARTMENT OF BIOCHEMISTRY V.V.Vanniaperumal College For Women, Virudhunagar, Tamil Nadu.

2. General structure of amino acids There are 20 commonly found standard α aminoacids Functional groups of amino acids include Coo - - carboxyl group, NH 3 + - amino group, R- Side chain

3. Classification of aminoacids Each AA is represented as 3 letter abbreviation and 1 letter symbol.

4. Classification of Amino Acids Based on polarity Nonpolar , aliphatic amino acids- Gly , Ala, Pro, Val, Leu , and Ile Polar, uncharged amino acids- Ser, Thr , Cys , Asn , Gln and Met Aromatic amino acids- Phe , Tyr and Trp. Phe and Tyr: benzene rings.Tryptophan : indole ring. Acidic amino acids- Asp and Glu Basic amino acids- Lys, Arg , and His.

5. Non standard aminoacids 4-Hydroxyproline and 5-hydroxylysine in collagen. 6-N-Methyllysine in myosin Ornithine and citrulline

6. Essential and non-essential amino acids Nonessential amino acids can be made by the body, while essential amino acids cannot be made by the body so obtained from diet.

7. Aromatic amino acids Phenylalanine An essential α- amino acid with the formula C6H5CH2CH(NH2)COOH. Classified as neutral and nonpolar because of the inert and hydrophobic nature of the benzyl side chain. The codons for L- phe are UUU and UUC. Dietary Sources: Naturally found in - breast milk of mammals. Good sources - are eggs, chicken, liver, beef, milk, and soybeans. Other sources - spinach and leafy greens, tofu, amaranth leaves, and lupin seeds.

8. Roles & Uses: • Used in the manufacture of food and drink products. • Sold as a nutritional supplement for its reputed analgesic and antidepressanteffects . • The L-isomer is used to biochemically form proteins, coded for by DNA. The codons for L-phenylalanine are UUU and UUC. • Is a precursor for tyrosine, dopamine, norepinephrine ( noradrenaline ), and epinephrine (adrenaline), and the skin pigment melanin. • Starting compound used in the flavonoid biosynthesis in plants. • The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine

9. TRYPTOPHAN (TRP) • One of the 23 standard amino acids and an essential amino acid in the human diet. • Encoded in the standard genetic code as the codon UGG & Contains an indole functional group. • Only L-stereoisomer of trp is used in structural or enzyme proteins. • The D-stereoisomer is occasionally found in naturally produced peptides (e.g.-the marine venom peptide contryphan ). Dietary sources: • A routine constituent of most protein-based foods or dietary proteins. • Particularly plentiful in chocolate, oats, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, almonds, sunflower seeds, pumpkin seeds, spirulina , bananas, and peanuts. • Found at a high level in turkey meat.

10. Roles & uses: An essential amino acid & act as building blocks in protein biosynthesis Functions as a biochemical precursor for the compounds - Serotonin (a neurotransmitter), Niacin (a vitamin), Auxin (a phytohormone ). Sold over the counter in the US, Canada, and the UK as a dietary supplement for use as an antidepressant, anxiolytic , and sleep aid. Also marketed for the indication of major depression under various trade names. Available in health food stores as a dietary supplement. Potential side effects of trp include nausea, diarrhea, drowsiness,headache , dry mouth, blurred vision, euphoria, and nystagmus (involuntary eye movements) etc.

11. TYROSINE (TYR) • Tyr or 4-hydroxyphenylalanine (from Greek tyros,meaning cheese), is one of the 23 amino acids that are used by cells to synthesize proteins. • A non-essential amino acid with a polar side group. • Its codons are UAC and UAU. Dietary sources: Found in many high-protein food products such as chicken, turkey, fish, milk, yogurt, cottage cheese,cheese , peanuts, almonds, pumpkin seeds, sesame seeds, soy products, lima beans, avocados, and bananas. Can also be synthesized in the body from phenylalanine by the enzyme phenylalanine hydroxylase .

12. Roles & Uses: Precursor to neurotransmitters and hormones, alkaloids, natural phenols, pigments (melanin). Tyrosine (or its precursor phenylalanine) is needed to synthesize the benzoquinone structure which forms part of coenzyme Q10. Useful during conditions of stress, cold, fatigue, prolonged work and sleep deprivation. Reductions in stress hormone levels & stress-induced weight loss seen in animal trials. Increases plasma neurotransmitter levels (particularly dopamine and norepinephrine ).

13. Metabolism of Aromatic amino acids Synthesis of aromatic amino acids follows Shikimate pathway which leads to the formation of chorismate .

14. Prephenic acid is then synthesized by a Claisen rearrangement of chorismate by Chorismate mutase . Which can then be utilized for: Tyrosine biosynthesis: Prephenate is oxidatively decarboxylated with retention of the hydroxyl group to give phydroxyphenylpyruvate , which is transaminated using glutamate as the nitrogen source to give tyrosine and α- ketoglutarate . Phenylalanine biosynthesis: Prephenate is converted to phenylpyruvate by prephenate dehydratase.Then phenylpyruvate is transaminated to give phenylalanine by phenylalanine aminotransferase .

15. Tryptophan biosynthesis: Chorismate produces anthranilate which condenses with phosphoribosylpyrophosphate (PRPP) to make N-5-Phosphoribosyl anthranilate.After ring opening of the ribose moiety and following reductive decarboxylation , indole-3-glycerolphosphate is produced, which in turn is transformed into indole.In the last step, tryptophan synthase catalyzes the formation of tryptophan from indole and the amino acid serine.

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