Dr.S.Chakravarty,MD
• 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
1. Glutamate :
NH3
Alpha keto Glutarate
Glutamate
dehydrogenase
Glutamate
Glutamate Dehydrogenase
2. Glutamine:
NH3
Glutamate
Glutamine
Glutamine synthase
Glutamine
syhthetase
Transamination reactions
3. Alanine:
Pyruvate
Glutamate
ALT
PLP
Alanine
Alpha keto glutarate
4. Aspartate :
AST
Oxaloacetate
Glutamate
PLP
Aspartate
Alpha keto glutarate
5. Asparagine:
NH3
Aspartate
Asparagine
Asparagine synthase
6. Tyrosine :
Phenylalanine
THB
DHB
Tyrosine
Phenyl alanine Hydroxylase
7. Glycine -
Glycine amidotransferases synthesize glycine
from glyoxylate and glutamate or alanine.
Two other reactions make glycine :-
serine hydroxymethytransferase
reaction(freely reversible)
• 8. Serine :- Two ways to make it
– Reversal of serine hydroxymethytransferase
reaction
9. Proline – from
Glutamate
-reversal reaction of
proline catabolism
Methionine
Methionine adenosyl transferase
THF
ATP
10. Cysteine:
S- Adenosyl Methionine
Acceptor
Methyl transferase
CH3-acceptor
S- Adenosyl Homocystiene
Homocysteine methyl
Transferase
(CH3 1-carbon )B12
Homocysteine
Serine
B6
Cystathionine β synthase
Methyl THF
Cystathionine
Cystathioninase
B6
Cysteine
Alpha-keto butyrate
• Phenylalanine – essential
• Tyrosine – non essential
• Tryptophan – essential
SYNTHESIS OF
THYROID
HORMONES
MELANIN
SYNTHESIS
TYROSINE
CATABOLISM TO
ACETOACETIC ACID
(KETOGENIC ) +
FUMARIC ACID
SYNTHESIS OF
CATECHOLAMINES eg
Epinephrine and
Norepinephrine
Dihydrobiopterin reductase
Phenylalanine
Phenylalanine hydroxylase
Tyrosine
THB
Tyrosine Hydroxylase
DHB
DOPA
co2
B6
DOPA Decarboxylase
Arvid Carlsson
M.D.
Nobel Prize
Dopamine 2000
β oxidase
alongwith
Eric Kandel and
Paul Greengard.
Dopamine
Dihydrobiopterin
reductase
Important – alpha methyl DOPA
inhibits dopa decarboxylase and
prevents hypertension by decreasing
epinephrine
Ascorbate(Vitamin C)
O2,
Cu2+
Dehydro-Ascorbate
Nor-Epinephrine
S- Adenosyl Methionine (SAM)
Phenylethanolamine N-methyl
Transferase (NMT)
Catechol-o-methyl Transferase
(COMT)
Epinephrine
S- Adenosyl Homocysteine (SAH)
mono amine oxidase(MAO)
metanephrine
Vanillyl mandelic
acid
• 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
IMPORTANCE OF VMA estimation
• Some tumors like Pheochromocytoma
(epinephrine excess ) or Neuroblastoma
• Excess of VMA in urine  Lab analysis
Tyrosine
Tyrosinase
Copper
(Melanoblasts )
DOPA
Copper
Tyrosinase
(Melanoblasts )
Dopaquinone
Several steps
TYROSINASE
IS
ABSENT
IN
ALBINISM
NO MELANIN
Melanin
THIS ALSO EXPLAINS HYPOPIGMENTATION IN PHENYLKETONURIA !!
• T3  Triiodothyronine
• T4  Thyroxine
Catabolism of phenylalanine
and tyrosine
USMLE !!
Phenylalanine
Phenylketonuria
Phenyl alanine Hydroxylase
Tyrosine
Tyrosinemia- II
Tyrosine Aminotransferase
Parahydroxyphenyl
pyruvate
Cu, Vit C
P-Hydroxyphenyl pyruvate hydroxylase
Homogentisic acid
Alkaptonuria
Tyrosinemia- I
Fumarate
Homgentisate oxidase
Fumaryl acetoacetate
hydrolase
Acetoacetate
1
Type II TYROSINEMIA
2
NEONATAL TYROSINEMIA
3
ALKAPTONURIA
4
TYPE I TYROSINEMIA
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
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
Phenylketonuria
Phenylalanine
Phenylalanine hydroxylase
defect
(-)
Dihydrobiopterin reductase
defect
Phenylpyruvate
Phenyl Lactate
Tyrosine
Phenyl acetate
Phenyl acetyl Glutamine
ALTERNATE
ROUTES OF
METABOLISM OF
PHENYLALANINE
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.
Amino Acid Disorders
Argininosuccinic aciduria (ASA)
NEONATAL SCREENING IN FLORIDA
Citrullinemia, type I (CIT)
(SOURCE CDC website and http://www.babysfirsttest.org)
Classic phenylketonuria (PKU)
Homocystinuria (HCY)
Hemoglobin Disorders
• Mousy/
of urine – phenyl acetate,
phenyl lactate
and phenylpyruvate
Maple
syrup urineMusty
diseaseodor
(MSUD)
S, Beta-thalassemia
(Hb S/ßTh)
Tyrosinemia,
type I (TYR I)
S, C disease (Hb S/C)
in urine.
Tyrosinemia, type II (TYR II)
Sickle cell anemia (Hb SS)
•
National
biochemical
screening
programme
Endocrine Disorders
Organic Acid Conditions
Congenital
adrenal
hyperplasia
3-Hydroxy-3-methylglutaric
aciduria
(HMG)or
• Blood
sample
– Heel(CAH)
 filter paper  analytical
laboratory ( PCR
+ HPLC
Primary congenital hypothyroidism (CH)
3-Methylcrotonyl-CoA carboxylase deficiency (3-MCC)
TANDEM MASS SPECTROMETRY)
Beta-ketothiolase deficiency (BKT)
– Screens diseases like :Glutaric acidemia type I (GA1)
Fatty Acid Oxidation Disorders
Holocarboxylase synthetase deficiency (MCD)
• Cystic fibrosis
Carnitine acylcarnitine translocase deficiency (CACT)
Isovaleric acidemia (IVA)
• PKU
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
• Congenital hypothyroidism
Carnitine uptake defect (CUD)
deficiency) (MUT)
Glutaric acidemia,
type II (GA-2)
Propionic acidemia
(PROP)
• Medium
chain acyl CoA dehydrogenase
deficiency
Long-chain L-3 hydroxyacyl-CoA dehydrogenase
Other Disorders
•
FeCl
test
–
Ferric
chloride
test.
3
deficiency (LCHAD)
Biotinidase deficiency (BIOT)
Medium-chain acyl-CoA dehydrogenase deficiency
Classic galactosemia (GALT)
(MCAD)
Cystic fibrosis (CF)
•
Guthrie
test:
Gold
standard
of
the
past
Short-chain acyl-CoA dehydrogenase deficiency (SCAD) Hearing loss (HEAR)
Trifunctional
protein strains
deficiency
Severe
combined growth
immunodeficiency
(SCID) growth
– Certain
of (TFP)
Bacillus Subtilis need Phe
as essential
factor.Bacterial
Very long-chain
acyl-CoA
dehydrogenase
deficiency
cannot
occur
in medium devoid
of Phe.
(VLCAD)
Cont..
– So, bactera will grow if blood containing Phe is added = PHENYLKETONURIA
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 .
Phenylketonuria
Phenylalanine Hydroxylase def
Dihydrobiopterin reductase def
• Normal levels of dopamine
• Low levels of dopamine
• Normal levels of prolactin
• High levels of prolactin
• Normal levels of
catecholamines
• Low levels of
cathecolamines
• Normal levels of tryptophan
and serotonin
• Increased tryptophan and
decreased serotonin
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
I
N
D
I
C
A
N
Niacin
Catabolized to
Acetoacetyl CoA
(KETOGENIC )
+
alanine (Glucogenic )
Synthesis of Serotonin
and Melatonin
Tryptophan
THB
Tryptophan Hydroxylase
DHB
5-HydroxyTryptophan
NADP
NADPH + H +
PLP
A.A. decarboxylase
Monoaminooxidase-A
(MAO)
5-HydroxyTryptamine
(Serotonin)
Acetyl CoA
Acetylation
Acetylation
N-acetyl Serotonin
methylation
Melatonin
SAM
SAH
5 HYDROXY INDOLE
ACETIC ACID ( HIAA)
Serotonin
MAO-A inhibitors
(Anti-Depressants)
(-)
Monoaminooxidase-A
(MAO)
5- Hydroxy indole acetic
acid (HIAA)
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
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?
A.
B.
C.
D.
E.
Glutamate decarboxylase
Monoamine oxidase
Tyrosine hydroxylase
DOPA decarboxylase
COMT (catechol O-methyl transferase)
Tryptophan
Tryptophan pyrrolase
N-formyl kynurenine
THFA
Kynurenine formylase
Formyl THFA  1 CARBON POOL
3-hydroxykynurenine
Kynureninase
H2O
PLP
Alanine
3-hydroxy Anthranilic
acid(HIAA )
NAD, NADP (Niacin)
60mg tryptophan = 1 mg NIACIN
Xanthurenic acid
TCA cycle
Acetyl Co-A
Acetoacetyl Co-A
A.
1.
2.
3.
4.
5.
Carcinoid syndrome :- (Argentaffinomas )
Neuroendocrine tumors – Midgut, bronchus
Excessive serotonin and kallikrenin.
Diarrhoea , flushing, abdominal cramps,
Heart failure – damage to valves
Diagnosis : HIAA in urine
• Pellagra like synptoms : Def of B6 or
Tryptophan
Diarrhoea, Dementia and Dermatitis
• Remember – Hartnups disease
• Melatonin: promotes sleep – sleep wake cycle
1. Hormone of the dark – blue light inhibits
melatonin synthesis.
2. Lowers Leptin levels
• Tryptophan load test – B6 deficiency
Depression
• Decrease in serotonin levels in CNS
• Treatment :
1. MAO-A inhibitors
2. SSRIs – selective serotonin reuptake
inhibitors
Mcq
• The non essential amino acid that becomes
essential in PKU is :• A. Phenylanaline
• B.Tyrosine
• C.Tryptophan
• D. ALANINE
• E. Cysteine
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