Amino acid biosynthesis grp assignment ppt

M.Sc. course assignment presentation slides

1. AMINO ACID BIOSYNTHESIS Oladele Foluke Wemimo Alade Aristotle Offor Gloria Nwabugwu Lecturer: Prof. E.E.J. Iweala

2. Outline Introduction Synthesis of amino acids t he Glutamate family Histidine biosynthesis the Serine family the Aromatic family the Pyruvate family the Aspartate family Regulation of amino acid biosynthesis Diseases of amino acid metabolism Conclusion References 8/24/2015 2

3. introduction All amino acids are derived from intermediates in glycolysis , the citric acid cycle, or pentose phosphate pathway. Nitrogen enters these pathways by way of glutamate and glutamine. Organisms vary greatly in their ability to synthesize the 20 common amino acids. Whereas most bacteria and plants can synthesize all 20, mammals can synthesize about half of them- generally those with simple pathways: the non-essential amino acids not needed in the diet. The remainder, the essential amino acids must be obtained from food. 8/24/2015 3

4. Essential and non-essential amino acids in humans 8/24/2015 4 Arg is essential in infants and children Most synthesized Arg  Ornithine and Urea via the urea cycle Cys gets its sulfur atom from Met Tyr is hydroxylated Phe So it’s not really non-essential

5. AMINO ACID BIOSYNTHESIS OVERVIEW ( USE OF COMMON INTERMEDIATES) 8/24/2015 5 GLUCOSE  GLUC-6-PHOSPHATE    RIB-5-PHOS→ HIS   3-PHOSPHOGLYCERATE  SERINE    GLYCINE E-4-PHOS + PEP CYSTEINE   PHE→ TYR PYRUVATE  ALA TRP  VAL CITRATE LEU, ILE ↓ OXALOACETATE, -KETOGLUTARATE ASP, ASN GLU, GLN, PRO, ARG, LYS, THR, MET

6. The glutamate family Glu - Ketoglutarate + AA  Glutamate + - Ketoacid Gln GLU + ATP + NH 3  GLN + ADP + p i Glutamine synthetase NH 3 is toxic; it’s stored as Gln GLN DONATES AMINO GPS IN MANY REACTIONS 8/24/2015 6

7. Arg , pro 8/24/2015 7 PRO, ORNITHINE, ARG ARE DERIVED FROM GLUTAMATE Step 1: Activate Glu ; a kinase Glutamate-5-semialdehyde branch point Spontaneous cyclization to an internal schiff base  Pro Transamination to Ornithine  Arg in urea cycle

8. HISTIDINE BIOSYNTHESIS Atoms derived from: 5-Phosphoribosyl- -pyrophosphate Provides 5 c-atoms Prpp involved in purine synthesis Prpp involved in pyrimidine synthesis Purine salvage pathway An intermediate in trp synthesis ATP provides the 6 th C-atom Gln supplies the second ring N 8/24/2015 8 T he products of the amido-transferase step: Aicar An intermediate in purine biosynthesis Imidazole glycerol phosphate ATP + -D-ribose-5-phosphate  Prpp + AMP -D-ribose-5-phosphate from H-M shunt

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10. The serine family 3-phosphoglycerate is precursor of Ser Gly Cys Ser (a 3-step pathway) (1) 3-PG + NAD +  3-phosphohydroxypyruvate + NADH+ H + (2) 3-PHP+ glu  3-phosphoserine + -KG (3) 3-phosphoserine + H 2 o  Ser + P i 8/24/2015 10

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12. Gly (2 different ways) (1) Ser + THF  Gly + N 5 ,N 10 – Methylene -THF (direct) (2) N 5 ,N 10 – Methylene -THF + CO 2 + NH 4 +  Gly + THF (CONDENSATION) 8/24/2015 12

13. Cysteine (in mammals) Ser + Homocysteine  Cystathionine Homocysteine is a breakdown product of methionine Cystathionine  - Ketobutyrate + Cys Note: -SH group comes from Met So Cys is actually an essential amino acid 8/24/2015 13

14. The aromatic family In plants and microrganisms Phe Tyr Trp Precursors are: Pep Erythrose-4-phosphate These condense with ultimate conversion to chorismate 8/24/2015 14

15. 8/24/2015 15 Chorismate Shikimate formed in steps 1-4 Chorismate formed in steps 5-7 Roundup Glycophate inhibites the enzyme that converts 5-Enolpyruvylshikimate 3–phosphate to chorismate , and hence blocks aromatic amino acid biosynthesis in plants. Animals lack this enz - herbicide fairly non-toxic

16. 8/24/2015 16 The Trp pathway Chorismate Branch point for trp synthesis Chorismate  anthranilate  trp Glutamine donates the N in the indole ring Condensation occurs with PRPP donating two carbons to the ring Tryptophan synthase Catalyzes final 2 steps Indole-3-glycerol phos  Indole + Glyc 3-p Indole + Ser  H 2 o + Trp

17. The Tyr and Phe pathway Chorismate  prephenate Prephenate Branch point for phe , tyr synth Aminotransferases in each final step In mammals, tyr is a product of: Phe hydroxylation 8/24/2015 17

18. The aspartate family 8/24/2015 18 Asp: non-essential amino acid one-step transamination reaction from oxaloacetate glu is the amino donor Asn : synthesized from Asp gln is the amino donor

19. Met, Thr and lys Asp- commom precursor of these essential amino acids Met Thr Lys First committed step is Asp + ATP  Aspartyl - β -phosphate + ADP Branch points occur at aspartate β - semialdehyde - an intermediate in all three pathways, and homoserine ,- a precursor of thr and met 8/25/2015 19

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21. THE Pyruvate family Ala: non-essential amino acid One-step transamination reaction from pyruvate . glu is the amino donor 8/25/2015 21

22. Leu , ile and val “branched chain essential amino acids” leu ile val Val, Ile: same pathway after 1 st step Leu pathway branches from val pathway final steps all catalyzed by amino- transferases glu is the amino donor 8/25/2015 22 the first step: Pyr + Tpp  hydroxyethyl-tpp first pyr and tpp form an adduct then decarboxylated to He- tpp adds to keto group of pyruvate  val , leu - ketobutyrate  ile

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24. Regulation of amino acid biosynthesis Feedback inhibition The first committed step in a biosynthetic pathway is usually the one that is regulated. Example: Isoleucine synthesis Threonine dehydratase is inhibited by isoleucine One of the first examples of allosteric feedback inhibition to be discovered. 8/25/2015 24

25. Concerted inhibition Allosteric inhibiton can be considerably more complex Example: glutamine synthetase of E.coli Six products derived from glutamine serve as negative feedback modulators of the enzyme. 8/25/2015 25

26. Enzyme multiplicity This prevents one biosynthetic end product from shutting down key pathway when other products of same pathway are required. Example: Aspartokinase 3 isozymes in E.coli each responds differently as far as feedback inhibition and repression of enzyme synthesis thr , lys , met pathways independently controlled ENZYME FEEDBACK INHIB ASP I THR ASP II MET ASP III LYS 8/25/2015 26

27. Sequential feedback inhibition in the synthesis of lys , met, and thr , one isozyme for the conversion of asp to aspartyl - β -phosphate is allosterically inhibited by two different modulators, lys and ile . The sequence from asp to ile undergoes multiple overlapping negative feedback inhibition; eg ile inhibits the conversion of thr to α - ketobutyrate and thr inhibits its own formation at three points: From homoserine , aspartate β - semialdehyde and aspartate 8/25/2015 27

28. Diseases of amino acid metabolism 8/25/2015 28 Hundreds of human metabolic diseases involving single-gene defects (often termed inborn errors of metabolism ) have been discovered. Many are due to defects in the breakdown of amino acids . Inherited defects may be expressed as a total loss of enzyme activity or, more frequently, as a partial deficiency in catalytic activity. Without treatment, this almost invariably result in mental retardation or other developmental abnormalities as a consequence of harmful accumulation of metabolites. Methods for analysing amino acids include: TLC, HPLC, GCMS, TMS etc.

29. Some human genetic disorders affecting amino acid catabolism 8/25/2015 29

30. phenylketonuria One of the most common disorders of amino acid metabolism. Cause: Deficiency of phenylalanine hydroxylase or a defect in biosynthesis/reduction of tetrah y drobiopterin . Phenylalanine hydroxylase :Mixed function oxidase that uses cofactor (tetrahydrobiopterin ) and molecular oxygen . Symptoms: Urinary excretion of pheny l p y ruvate and phenyllactate , d efective neural development , s evere mental retardation , and v ery light skin pigmentation Therapy: Diet restricted in phenylalanine but supplemented with tyrosine or Replacement therapy with BH4 or L-DOPA and 5-hydroxytryptophan. Screening: Newborns are routinely screened for PKU by testing for elevated levels of phenylpyruvate in the urine or of phenylalanine in the blood during the first days after birth. 8/25/2015 30

31. alkaptonuria The first metabolic disease to be characterized as a genetic defect by Archibald Garrod in 1902. Also known as black urine disease. Cause: Lack of homogentisate oxidase the enzyme that cleaves homogentisic acid. Symptoms: the patient’s urine contains elevated levels of homogentisic acid, which is oxidized to a dark pigment on standing , large joint arthritis, and black ochronotic pigmentation of cartilage and collagenous tissue. Dark staining of the diapers sometimes can indicate the disease in infants, but usually no symptoms are present until later in life (about age 40). Therapy: Diets low in protein—especially in phenylalanine and tyrosine 8/25/2015 31 Fig: Phenylalanine degradation

32. Albinism Defect in tyrosine metabolism results in a deficiency in the production of melanin. Partial or full absence of pigment from the skin, hair, and eyes . Cause: Lack of tyrosinase Symptoms: Affected individuals have vision defects and photophobia (sunlight hurts their eyes). They are at increased risk for skin cancer. 8/25/2015 32 Fig: Patient with oculocutaneous albinism, showing white eyebrows and lashes.

33. Maple syrup urine disease Recessive disorder Cause: partial or complete deficiency in branched-chain α- keto acid dehydrogenase —an enzyme that decarboxylates leucine , isoleucine , and valine . Levels of branched-chain α-amino acids and their α- keto analogs are elevated in plasma and urine. Enzyme requires five cofactors (thiamine pyrophosphate, FAD , NAD, lipoate , and coenzyme A) Symptoms: feeding problems , vomiting, dehydration, severe metabolic acidosis, and a characteristic smell of the urine. If untreated, the disease leads to mental retardation, physical disabilities, and death . Treatment: synthetic formula that contains limited amounts of leucine , isoleucine , and valine . 8/25/2015 33 Fig: Catabolic pathways for the three branched-chain amino acids: valine , isoleucine , and leucine .

34. homocystinuria Defects in the metabolism of homocysteine . Cause: deficiency in cystathionine synthase . Accumulation of homocysteine occurs in the urine. Methionine and its metabolites are elevated in the blood. Symptoms: Mental retardation, osteoporosis, myocardial infarction, and a characteristic dislocation of the lens occur. Treatment: restriction of methionine intake and supplementation with vitamins B6, B12, and folate . 8/25/2015 34 Fig: Enzyme deficiency in homocystinuria

35. conclusion Amino acids are required for many vital functions of an organism. Mammals can either synthesize amino acids from common keto acid carbon skeletons and preformed amino nitrogen such as that of glutamate or obtain them from their diets. The biosynthesis of nonessential amino acids involves relatively simple pathways, whereas those forming the essential amino acids are generally more complex. The amino acid biosynthetic pathways are subject to allosteric end-product inhibition; the regulatory enzyme is usually the first in the sequence. Regulation of the various synthetic pathways is coordinated. Some important genetic diseases associated with amino acid metabolism include phenylketonuria , albinism , homocystinuria , alkaptonuria , and maple syrup urine disease. 8/25/2015 35

36. references Devlin, T.M. (1997). Textbook of Biochemistry with clinical correlations. New York, 4 th edn . John W iley and Sons Inc. ISBN 0-471-15451-2. Harvey, R.A. and Ferrier, D.R. (2011). Lippincott’s illustrated reviews. Philadelphia, 5 th Edn . Lippincott W illiams and W ilkins. ISBN 978-1-60831-412-6. Horton, H.R., Moran, L.A., Perry, M.D. and Acrimgeour , K.G. (2012). Principles of biochemistry. USA, 5 th Edn . Pearson Education Inc. ISBN 0-321-70733-8. Nelson , D.L. and Cox, M.M.(2008). Lehninger Principles of Biochemistry. New York, 5 th Edition, W.H. Freeman and Company. ISBN: 978-0-7167-7108-1. Voet , D. and Voet , J.G. (2011). Biochemistry. USA, 4 th Edn , John Wiley & Sons Inc. ISBN 13: 978-0470-57095-1. 8/25/2015 36

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