1. Amino acid metabolism 1
Dr.S.Chakravarty,MD

2. Learning objectives
Explain the steps in synthesis of various non-essential amino acids in the body
List the molecules derived from aromatic amino acids and their uses
Discuss the enzyme deficiencies of aromatic amino acid metabolism and their clinical features
Differentiate various types of phenylketonuria and its diagnosis
Discuss the clinical features of Alkaptonuria and its treatment

3. Biosynthesis of Non Essential Amino-acids

4. TRANSAMINATION
DEF :- THE TRANSFER OF THE ALPHA-AMINO GROUP FROM ONE AMINO ACID TO A KETO ACID , RESULTING IN FORMATION OF A NEW AMINO ACID AND CORRESPONDING KETO ACID .
E.G :- REACTION CATALYZED BY ALANINE AMINOTRANSFERASE
ALANINE PYRUVATE
(AMINO ACID ) (CORRESPONDING KETO ACID )
Α-KETOGLUTARATE GLUTAMATE
(KETO ACID ) (NEW AMINO ACID)
ALT
PLP

5. USES OF TRANSAMINATION
FIRST STEP OF CATABOLISM OF PROTEINS
SYNTHESIS OF NON-ESSENTIAL AMINO ACIDS
INTERCONVERSION OF AMINO ACIDS
REGENERATION OF TCA CYCLE

6. 1. Glutamate : 2. Glutamine: NH3 Alpha keto Glutarate Glutamate NH3
Glutamate dehydrogenase
Alpha keto Glutarate
Glutamate
Glutamate Dehydrogenase
2. Glutamine:
NH3
Glutamate
Glutamine
Glutamine
syhthetase
Glutamine synthase

7. Transamination reactions
3. Alanine:
ALT
Pyruvate
Alanine
PLP
Glutamate
Alpha keto glutarate
4. Aspartate :
AST
Oxaloacetate
Aspartate
PLP
Glutamate
Alpha keto glutarate

8. 5. Asparagine: 6. Tyrosine : NH3 Aspartate Asparagine Tyrosine
Asparagine synthase
6. Tyrosine :
THB
DHB
Tyrosine
Phenylalanine
Phenyl alanine Hydroxylase

9. Phenylalanine hydroxylase reaction

10. 7. Glycine - Glycine amidotransferases synthesize glycine from glyoxylate and glutamate or alanine.
Two other reactions make glycine :-
serine hydroxymethytransferase reaction(freely reversible)

11. 8. Serine :- Two ways to make it
Reversal of serine hydroxymethytransferase reaction

12. 9. Proline – from Glutamate -reversal reaction of proline catabolism

13. 10. Cysteine: Methionine THF S- Adenosyl Methionine
Methionine adenosyl transferase
ATP
10. Cysteine:
S- Adenosyl Methionine
Acceptor
CH3-acceptor
Methyl transferase
Homocysteine methyl Transferase
S- Adenosyl Homocystiene
(CH3 1-carbon )B12
Homocysteine
Serine
Methyl THF B6
Cystathionine β synthase
Cystathionine B6
Cystathioninase
Cysteine
Alpha-keto butyrate

14. Metabolism of
Aromatic amino acids

15. Metabolism of Aromatic amino acids:
Phenylalanine – essential
Tyrosine – non essential
Tryptophan – essential

16. PHENYLALANINE
AND
TYROSINE

17. FATES OF TYROSINE IN BODY
MELANIN SYNTHESIS
SYNTHESIS OF THYROID HORMONES
TYROSINE
CATABOLISM TO ACETOACETIC ACID (KETOGENIC ) + FUMARIC ACID
SYNTHESIS OF CATECHOLAMINES eg
Epinephrine and Norepinephrine

18. SYNTHESIS OF TYROSINE FROM PHENYLALANINE
Dihydrobiopterin reductase
Phenylalanine
hydroxylase
reaction

19. Vanillyl mandelic acid metanephrine
Catecholamine synthesis
Phenylalanine
Phenylalanine hydroxylase
Tyrosine
THB
Dihydrobiopterin reductase
Tyrosine Hydroxylase
DHB
DOPA
Important – alpha methyl DOPA inhibits dopa decarboxylase and prevents hypertension by decreasing epinephrine
co2
DOPA Decarboxylase B6
Dopamine
Arvid Carlsson
M.D.
Nobel Prize
2000 alongwith
Eric Kandel and Paul Greengard.
Ascorbate(Vitamin C)
O2, Cu2+
Dopamine β oxidase
Dehydro-Ascorbate
Nor-Epinephrine
S- Adenosyl Methionine (SAM)
Phenylethanolamine N-methyl Transferase (NMT)
S- Adenosyl Homocysteine (SAH)
Epinephrine
Catechol-o-methyl Transferase (COMT)
mono amine oxidase(MAO)
Vanillyl mandelic acid
metanephrine
CNS and ADRENAL MEDULLA

20. Diseases associated with catecholamine synthesis:
Schizophrenia – Dopamine overproduction
Parkinson’s disease :
Damage to Nigro-striatal tract - Dopamine
Treatment: – Levo-DOPA + Carbidopa
Carbidopa is PERIPHERAL DOPA-DECARBOXYLASE INHIBITOR it increases the plasma half-life of levodopa from 50 minutes to 1½ hours. Carbidopa cannot cross the blood brain barrier, so it inhibits only peripheral DDC.
It thus prevents the conversion of L-DOPA to dopamine peripherally
Pheochromocytoma
Neuroblastoma
Increased catecholamine production

22. IMPORTANCE OF VMA estimation
Some tumors like Pheochromocytoma (epinephrine excess ) or Neuroblastoma
Excess of VMA in urine  Lab analysis

23. Formation of Melanin Tyrosine DOPA Dopaquinone Melanin Tyrosinase
Copper
Tyrosinase
(Melanoblasts )
TYROSINASE IS
ABSENT IN
ALBINISM
NO MELANIN
DOPA
Tyrosinase
(Melanoblasts )
Copper
Dopaquinone
Several steps
Melanin
THIS ALSO EXPLAINS HYPOPIGMENTATION IN PHENYLKETONURIA !!

24. Formation of thyroid hormones
T3  Triiodothyronine
T4  Thyroxine

25. Phenylalanine Tyrosine Fumarate
Catabolism of phenylalanine and tyrosine
USMLE !!
Phenylalanine
Phenylketonuria
Phenyl alanine Hydroxylase
Tyrosine
Tyrosinemia- II
Tyrosine Aminotransferase
PLP
Parahydroxyphenyl pyruvate
P-Hydroxyphenyl pyruvate hydroxylase
Cu, Vit C
Homogentisic acid
Alkaptonuria
Homgentisate oxidase
Tyrosinemia- I
Fumaryl acetoacetate hydrolase
Fumarate
Acetoacetate

26. CATABOLISM OF TYROSINE1
Type II TYROSINEMIA 2
NEONATAL TYROSINEMIA 3
ALKAPTONURIA 4
TYPE I TYROSINEMIA

27. Tyrosinemia Type 1 Defect in fumarylacetoacetate hydrolase
Plasma tyrosine levels elevated (6-12mg/dl)]
ACUTE FORM – FATAL BY 6-8 MONTHS
CHRONIC FORM- 10 YEARS
DIARRHOEA
VOMITING
CABBAGE LIKE ODOR
LIVER FAILURE
URINE :-tyrosine, p -hydroxyphenyl pyruvate,
P- hydroxyphenyl lactate , p- hydroxyphenyl acetate

28. Tyrosinemia Type II (Richner Hanhart Syndrome)
DEF. OF TYROSINE AMINOTRANSFERASE
Mental retardation
Keratosis of palmar surface
Painful corneal lesions
Photophobia
NEONATAL TYROSINEMIA
Def . Of p-hydroxyphenyl pyruvate hydroxylase

29. Phenylketonuria (-) Phenylalanine Tyrosine Phenylpyruvate
Phenylalanine hydroxylase defect
(-)
Transaminase
Dihydrobiopterin reductase defect
Tyrosine
Phenylpyruvate
Reduction
ALTERNATE ROUTES OF METABOLISM OF PHENYLALANINE
Decarboxylation
Phenyl Lactate
Phenyl acetate
Conjugation with glutamine
Phenyl acetyl Glutamine

30. Phenylketonuria
USMLE !!
Autosomal recessive disease – MC disorder of amino acid metabolism
Def of phenylalanine hydroxylase or
Dihydrobiopterin reductase.
Increased phenylalanine in the blood
Saturates – LNAAT (large neutral aminoacid transporter system of brain).
mental retardation, seizures-
Poor protein and neurotransmitter synthesis in brain
Toxicity from accumulating alternate metabolites like phenylketones
Decreased pigmentation of skin and eyes.

31. Amino Acid Disorders
Argininosuccinic aciduria (ASA)
NEONATAL SCREENING IN FLORIDA
Citrullinemia, type I (CIT)
(SOURCE CDC website and
Classic phenylketonuria (PKU)
Homocystinuria (HCY)
Hemoglobin Disorders
Maple syrup urine disease (MSUD)
S, Beta-thalassemia (Hb S/ßTh)
Tyrosinemia, type I (TYR I)
S, C disease (Hb S/C)
Tyrosinemia, type II (TYR II)
Sickle cell anemia (Hb SS)
Endocrine Disorders
Organic Acid Conditions
Congenital adrenal hyperplasia (CAH)
3-Hydroxy-3-methylglutaric aciduria (HMG)
Primary congenital hypothyroidism (CH)
3-Methylcrotonyl-CoA carboxylase deficiency (3-MCC)
Beta-ketothiolase deficiency (BKT)
Glutaric acidemia type I (GA1)
Fatty Acid Oxidation Disorders
Holocarboxylase synthetase deficiency (MCD)
Carnitine acylcarnitine translocase deficiency (CACT)
Isovaleric acidemia (IVA)
Carnitine palmitoyltransferase I deficiency (CPT-IA)
Methylmalonic acidemia (cobalamin disorders) (Cbl A,B)
Carnitine palmitoyltransferase type II deficiency (CPT-II)
Methylmalonic acidemia (methymalonyl-CoA mutase deficiency) (MUT)
Carnitine uptake defect (CUD)
Glutaric acidemia, type II (GA-2)
Propionic acidemia (PROP)
Long-chain L-3 hydroxyacyl-CoA dehydrogenase deficiency (LCHAD)
Other Disorders
Biotinidase deficiency (BIOT)
Medium-chain acyl-CoA dehydrogenase deficiency (MCAD)
Classic galactosemia (GALT)
Cystic fibrosis (CF)
Short-chain acyl-CoA dehydrogenase deficiency (SCAD)
Hearing loss (HEAR)
Trifunctional protein deficiency (TFP)
Severe combined immunodeficiency (SCID)
Very long-chain acyl-CoA dehydrogenase deficiency (VLCAD)
Cont..
Mousy/ Musty odor of urine – phenyl acetate, phenyl lactate and phenylpyruvate in urine.
National biochemical screening programme
Blood sample – Heel  filter paper  analytical laboratory ( PCR + HPLC or TANDEM MASS SPECTROMETRY)
Screens diseases like :-
Cystic fibrosis
PKU
Congenital hypothyroidism
Medium chain acyl CoA dehydrogenase deficiency
FeCl3 test – Ferric chloride test.
Guthrie test: Gold standard of the past
Certain strains of Bacillus Subtilis need Phe as essential growth factor.Bacterial growth cannot occur in medium devoid of Phe.
So, bactera will grow if blood containing Phe is added = PHENYLKETONURIA

32. Treatment Early detection is VERY IMPORTANT !!
Diet containing low phenylalanine
( but NEVER ZERO Phe!!)
FOOD BASED ON TAPIOCA (CASSAVA ) IS HELPFUL
SPECIAL DIET TILL 5YEARS OF AGE
SPECIAL DIET AGAIN IF PERSON IS PREGNANT LATER ON Excess Phe affects brain development of fetus .

33. Phenylketonuria Normal levels of dopamine Low levels of dopamine
Phenylalanine Hydroxylase def
Dihydrobiopterin reductase def
Normal levels of dopamine
Normal levels of prolactin
Normal levels of catecholamines
Normal levels of tryptophan and serotonin
Low levels of dopamine
High levels of prolactin
Low levels of cathecolamines
Increased tryptophan and decreased serotonin

34. Alkaptonuria Autosomal Recessive
Deficient enzyme: Homogentisate 1,2-dioxygenase/ (Oxidase)
conversion of homogentisic acid (product of tyrosine metabolism) to maleylacetoacetate (→ acetoacetate → Fumarate → TCA)
Pathology
Homogentisic acid accumulates, auto-oxidizes
Oxidized homogentisate polymerizes, forms dark-colored pigment
Purplish black color of urine on standing
Precipitates of dark homogentisic acid (Alkaptan bodies) deposit in connective tissue discoloration (ochronosis)
e.g. in cartilage, joints, ear wax
vertebrae
deposits cause Arthralgia (joint pain)
sometimes associated with degenerative arthritis

36. Main Fates of TryptophanD C A
Niacin
Catabolized to Acetoacetyl CoA (KETOGENIC ) +
alanine (Glucogenic )
Synthesis of Serotonin and Melatonin

37. MELATONIN SYNTHESIS Tryptophan 5-HydroxyTryptophan 5-HydroxyTryptamine
THB
NADP
Tryptophan Hydroxylase
DHB
NADPH + H +
5-HydroxyTryptophan
PLP
A.A. decarboxylase
Monoaminooxidase-A
(MAO)
5-HydroxyTryptamine
(Serotonin)
Acetyl CoA
5 HYDROXY INDOLE ACETIC ACID ( HIAA)
Acetylation
MELATONIN
SYNTHESIS
Acetylation
N-acetyl Serotonin
SAM
methylation
SAH
Melatonin

38. Catabolism of serotonin
MAO-A inhibitors
(Anti-Depressants)
Monoaminooxidase-A
(MAO)
(-)
5- Hydroxy indole acetic acid (HIAA)

39. MAO- mono amino oxidase
Epinephrine, norepinephrine, serotonin and melatonin are metabolised by MAO- A enzymes
Dopamine, Tyramine and tryptamine are metabolised by both MAO-A and MAO-B
Tyramine mimics catecholamines in their actions

40. Cheese reaction
A patient presents with headaches, palpitations, nausea and vomiting and elevated blood pressure. These symptoms appear after the person has eaten a large meal containing aged cheeses and wine. The patient’s history indicates that he is on some medicaton for a different condition. Assuming that the medication is in some way involved in these symptoms, which enzyme might be the target of this drug?
Glutamate decarboxylase
Monoamine oxidase
Tyrosine hydroxylase
DOPA decarboxylase
COMT (catechol O-methyl transferase)

41. Tryptophan catabolism
Tryptophan pyrrolase
N-formyl kynurenine
THFA
Kynurenine formylase
Formyl THFA  1 CARBON POOL
3-hydroxykynurenine
Xanthurenic acid
H2O
Kynureninase
PLP
Alanine
3-hydroxy Anthranilic acid(HIAA )
TCA cycle
Acetyl Co-A
NAD, NADP (Niacin)
Acetoacetyl Co-A
60mg tryptophan = 1 mg NIACIN

42. Diseases associated with tryptophan Metabolism
Carcinoid syndrome :- (Argentaffinomas )
Neuroendocrine tumors – Midgut, bronchus
Excessive serotonin and kallikrenin.
Diarrhoea , flushing, abdominal cramps,
Heart failure – damage to valves
Diagnosis : HIAA in urine

43. Pellagra like synptoms : Def of B6 or Tryptophan
Diarrhoea, Dementia and Dermatitis
Remember – Hartnups disease
Melatonin: promotes sleep – sleep wake cycle
Hormone of the dark – blue light inhibits melatonin synthesis.
Lowers Leptin levels
Tryptophan load test – B6 deficiency

44. Depression Decrease in serotonin levels in CNS Treatment :
MAO-A inhibitors
SSRIs – selective serotonin reuptake inhibitors

45. Mcq The non essential amino acid that becomes essential in PKU is :-
A. Phenylanaline
B.Tyrosine
C.Tryptophan
D. ALANINE
E. Cysteine

46. Mcq The cause of light skin color in PKU is
A. decreased synthesis of melanin from Phe
B. decreased synthesis of melanin from Tyr
C. excess melanin synthesis from Phe
D. excess of phenylketones
E.mental retardation causes decreased melatonin

47. Thank you