Metabolism of Phenylalanine and Tyrosine
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Metabolism of Phenylalanine and Tyrosine.
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Metabolism of Phenylalanine and Tyrosine
- 3. Phenylalanine, tyrosine and tryptophan are the aromatic amino acids. Metabolism of these AAs deserves special mention, No. of biologically important compounds are produced from them. Deficiency of enzymes in the metabolic pathways of these AAs results in no. of inborn errors of clinical importance. Phenylalanine and tryptophan are nutritionally essential amino acids but tyrosine is not as it can be synthesized from phenylalanine. All are both glucogenic as well as ketogenic.
- 5. aromatic & essential amino acid Both Glucogenic & Ketogenic Phenylalanine is converted to tyrosine. Referred to as 'sparing action' of tyrosine on phenylalanine. P h e n y l a l a n i n e Phenylalanine – CH2-CH-COOH NH2 _
- 6. Overview of P h e n y l a l a n i n e a n d t y r o s i n e metabolism Phenylalanine tyrosine Protein Glucose Fat Thyroid hormones, (T3, T4) Norepinephrine, epinephrine (adrenal medulla) Dopamine (CNS) Melanin pigment (skin, hair, eye)
- 7. Conversion of Phenylalanine To tyrosine
- 8. Conversion of Phenylalanine To tyrosine Phenylalanine Tyrosine Dihydro- biopterin Tetrahydro- biopterin Phenylalanine hydroxylase NADP+ NADPH+H+ O2 H2O Dihydrobiopterin reductase – CH2-CH-COOH NH2 _ – CH2-CH-COOH NH2 _ HO – Monooxygenase
- 9. Degradation of Phenylalanine To tyrosine
- 10. Degradation of Phenylalanine To tyrosine Phenylalanine Tyrosine Phenylalanine hydroxylase – CH2-CH-COOH NH2 _ HO – – CH2-CH-COOH NH2 _ Tyrosine transaminase Glutamate α-ketoglutarate p-hydroxyphenylpyruvate HO – – CH2-C-COOH O =
- 11. Degradation of Phenylalanine To tyrosine p-hydroxyphenylpyruvate HO – – CH2-C-COOH O = p-HPP dioxygenase Homogentisate – CH2-COOH Dehydroascorbate H2O, CO2 Ascorbate Homogentisate oxidase 4-Maleylacetoacetate – CH2-COOHC CO- O O = O O2
- 12. Degradation of Phenylalanine To tyrosine 4-Maleylacetoacetate H-C-C-CH2-C-CH2-COOH H-C-COOH = = = O O Maleylacetoacetate isomerase Glutathione 4-Fumaylacetoacetate H-C-C-CH2-C-CH2-COOH HOOC-C-H = = = O O
- 13. Degradation of Phenylalanine To tyrosine 4-Fumarylacetoacetate H-C-C-CH2-C-CH2-COOH HOOC-C-H = = = O O Fumarate H-C-COOH HOOC-C-H = Acetoacetate CH3-C-CH2-COOH = O Glucose Acetyl CoA Lipids Fumarylacetoacetate hydrolase
- 14. Phenylalanine Tyrosine Phenylalanine hydroxylase Tyrosine transaminase p-hydroxyphenylpyruvate p-HPP dioxygenase Homogentisate Homogentisate oxidase 4-Maleylacetoacetate Maleylacetoacetate isomerase 4-Fumaylacetoacetate Fumarylacetoacetate hydrolase Fumarate Acetoacetate Phenylket onuria Tyrosinemia t ype II N eonat al t yrosinemia A lkapt onuria t yrosinemia t ype I
- 16. Biologically Important Compounds Derived from Tyrosine Tyrosine serves as a precursor for… Catecholamines Dopamine Norepinephrine Epinephrine Thyroid hormones T4 T3 Melanin pigment
- 17. synthesis of Catecholamines Epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine are collectively called catecholamines. They are synthesized from tyrosine. Epinephrine & norepinephrine are produced by adrenal medulla & serve as hormones. Whereas, dopamine and norepinephrine produced in the CNS & postganglionic sympathetic nerves act as neurotransmitter. In Parkinson’s disease, dopamine levels in the CNS are decreased because of a deficiency of cells that produce dopamine.
- 19. Functions of catecholamines Norepinephrine and epinephrine regulate carbohydrate and lipid metabolisms. They stimulate the degradation of triacylglycerol and glycogen. They cause an increase in the blood pressure. Dopamine and norepinephrine serve as neurotransmitters in the brain & autonomous nervous system.
- 20. Dopamine and Parkinson’s disease Parkinson’s disease is a common disorder in many elderly people, with about 1% of the population above 60 years being affected. It is characterized by… Muscular rigidity, Tremors, Expressionless face, Lethargy, Involuntary movements etc.
- 21. Dopamine and Parkinson’s disease Biochemical basis : The exact biochemical cause of this disorder has not been identified. It is, however, linked with a production of dopamine. The disease is due to degeneration of certain parts of the brain (substantia nigra and locus coeruleus), leading to the impairment in the synthesis of dopamine.
- 22. Dopamine and Parkinson’s disease Treatment : Dopamine cannot enter the brain, hence its administration is of no use. DOPA (levodopa or L-dopa) is used in the treatment of Parkinson’s disease. In the brain, DOPA is converted to dopamine which alleviates the symptoms of PD. Unfortunately, dopamine synthesis occurs in various other tissues & results in side-effects such as nausea, vomiting, hypretension etc. Administration of DOPA analogs—that inhibit dopa decarboxylase (in various tissues) but not enter brain (due to BBB)—are found to be effective. Carbidopa & γ-methyl-dopa (dopa analogs) are administered along with dopa for the treatment of Parkinson’s disease.
- 23. synthesis of Thyroid hormones CH2 Thyroglobulin OH Tyrosine residue CH2 Thyroglobulin OH I CH2 Thyroglobulin OH I I Active Iodine (I+) DIT Monoiodotyrosine Diiodotyrosine Triiodothyronine (T3) Thyroxine (T4)
- 24. DOPA H2O O2 Tyrosine hydroxylase Tyrosine H2-Biopterin H4- Biopterin Dopaquinone Tyrosinase H2O Leucodopachrome Red melanin Indole 5,6-quinone Tyrosinase synthesis of Melanin pigment O2 Dopachrome Cysteine 5,6-Dihydroxyindole Spontaneous BLACK MELANIN
- 25. Melanin —the colour pigment: The skin colour of the individual is determined by the relative conc. of black and red melanins. This, in turn, is dependent on many factors, both genetic and environmental. These include the activity of tyrosinase, the density of melanocytes, availability of tyrosine etc. Albinism is an inborn error with generalized lack of melanin synthesis.
- 26. ….