A. AMINO ACIDS
• Contains at least one of both amino and carboxylic acid functional groups.
• N-terminal end amino group (-NH2) and the C terminal end carboxyl group (-COOH) bond to
the alphacarbon with the amino group of one amino acid linking with the carboxyl group of
another → peptide bond.
• CHAIN OF AMINO ACIDS → polypeptide → protein
• Difference in amino acids depends on the chemical composition of the R group.
➢ METABOLISM
• Minimal synthesis in the body, must be supplied by the DIET.
• Essential amino acids: arginine, histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan, and valine
• Produced by the body: alanine, asparagine, aspartic acid, cysteine, glutamic acid,
glutamine, glycine, proline, serine, and tyrosine.
• Digestion: proteolytic enzymes (pepsin and trypsin) • Rapidly observed from the intestine
into the circulation.
• Amino acids - utilized for synthesis of → nonprotein nitrogen-containing compounds
(purines, pyrimidines, porphyrins, creatine, histamine, thyroxin, epinephrine, and the
coenzyme NAD).
➢ AMINO ACID DISORDERS
DISORDERS FACTS
Phenylketonuria • Enzyme activity (absent): phenylalanine hydroxylase (PAH)
(PKU)
• Converts phenylalanine to tyrosine is affected
• Accumulation of phenylalanine
• Urine: Musty odor
Tyrosinemia • Inborn metabolic disorders of tyrosine catabolism
• Urine metabolites: tyrosine and tyrosine catabolites
• Type I tyrosinemia:
✓ most severe form
✓ low levels of fumarylacetoacetate hydrolase
✓ failure to thrive, diarrhea, vomiting, jaundice, cabbage-like
odor, distended abdomen, swelling of legs and increased
predisposition for bleeding.
• Type II tyrosinemia
✓ low levels of tyrosine aminotransferase
✓ mental retardation, excessive tearing, photophobia, eye pain,
and redness and painful skin lesions.
• Type III tyrosinemia
✓ rare disorder
✓ low levels of 4-hydroxyphenylpyruvate dioxygenase
• Diagnosis: elevated tyrosine levels using MS/MS coupled with a
confirmatory test (increased levels of succinylacetone)
Alkaptonuria • Inborn metabolic disease
• Autosomal recessive gene (HGD)
• Low levels of enzyme: homogentisate oxidase
• Urine: turns brownish-black when mixed with air.
, • Autosomal recessive disorder
• Accumulation of branched-chain amino acids and their
corresponding ketoacids in the blood, urine, and CSF
• Neonatal screening: modified Guthrie’s test (metabolic inhibitor to
B. subtilis – 4 azaleucine)
ISOVALERIC ACIDEMIA • Autosomal recessive metabolic disorder
• Low levels of isovaleryl-CoA dehydrogenase
• Leucine is not metabolized
• Mutations in the isovaleryl CoA dehydrogenase ( IVD) gene
• “sweaty feet” odor of urine.
• Cause CNS problems
• Treatment: restrict diet of protein, glycine and carnitine intake.
Homocystinuria • Autosomal recessive disorder of amino acid metabolism
• Lack of enzyme: cystathionine-Beta synthetase → required for
methionine metabolism
• Increased methionine and homocysteine
• Associated with osteoperosis, dislocated lenses in the eye (collagen
deficiency), mental retardation
• Treatment: restrict methionine in diet, vitamin B6 supplementation,
& trimethylglycine, folic acid supplementation, cysteine
(sometimes).
• Guthrie’s test using L-methionine sulfoximine as metabolic inhibitor.
Cystinuria • Inherited autosomal recessive
• Amino acid transport system defect
• Inadequate reabsorption of cysteine during the filtering process in
the kidneys.
• Urine: formation of precipitates → stone formation in the urinary
tract
• Hematuria, pain in the side, UTI.
• Treatment: increase urine volume to reduce concentration of
cysteine (increased water consumption)
• Cyanide nitroprusside test → red purple color reaction with
sulfhydryl groups.
• Quantitative: Ion exchange chromatography
METHODS OF AMINO • Fasting: 6 – 8 hours
ACID ANALYSIS • Heparinized plasma
• Deproteinization → performed within 30 minutes of sample
collection and analysis should be performed immediately or the
sample frozen @ -200C to 400C.
• Quantitative urinary amino acid analysis: 24 hour urine sample
preserved in thymol or organic solvents is required.
• Screening test: Thin layer chromatography
• Quantification: Ion exchange chromatography, HPLC reversed-phase
system equipped with fluorescence detection or capillary
electrophoresis.
• MS/MS: highly sensitive
• Contains at least one of both amino and carboxylic acid functional groups.
• N-terminal end amino group (-NH2) and the C terminal end carboxyl group (-COOH) bond to
the alphacarbon with the amino group of one amino acid linking with the carboxyl group of
another → peptide bond.
• CHAIN OF AMINO ACIDS → polypeptide → protein
• Difference in amino acids depends on the chemical composition of the R group.
➢ METABOLISM
• Minimal synthesis in the body, must be supplied by the DIET.
• Essential amino acids: arginine, histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan, and valine
• Produced by the body: alanine, asparagine, aspartic acid, cysteine, glutamic acid,
glutamine, glycine, proline, serine, and tyrosine.
• Digestion: proteolytic enzymes (pepsin and trypsin) • Rapidly observed from the intestine
into the circulation.
• Amino acids - utilized for synthesis of → nonprotein nitrogen-containing compounds
(purines, pyrimidines, porphyrins, creatine, histamine, thyroxin, epinephrine, and the
coenzyme NAD).
➢ AMINO ACID DISORDERS
DISORDERS FACTS
Phenylketonuria • Enzyme activity (absent): phenylalanine hydroxylase (PAH)
(PKU)
• Converts phenylalanine to tyrosine is affected
• Accumulation of phenylalanine
• Urine: Musty odor
Tyrosinemia • Inborn metabolic disorders of tyrosine catabolism
• Urine metabolites: tyrosine and tyrosine catabolites
• Type I tyrosinemia:
✓ most severe form
✓ low levels of fumarylacetoacetate hydrolase
✓ failure to thrive, diarrhea, vomiting, jaundice, cabbage-like
odor, distended abdomen, swelling of legs and increased
predisposition for bleeding.
• Type II tyrosinemia
✓ low levels of tyrosine aminotransferase
✓ mental retardation, excessive tearing, photophobia, eye pain,
and redness and painful skin lesions.
• Type III tyrosinemia
✓ rare disorder
✓ low levels of 4-hydroxyphenylpyruvate dioxygenase
• Diagnosis: elevated tyrosine levels using MS/MS coupled with a
confirmatory test (increased levels of succinylacetone)
Alkaptonuria • Inborn metabolic disease
• Autosomal recessive gene (HGD)
• Low levels of enzyme: homogentisate oxidase
• Urine: turns brownish-black when mixed with air.
, • Autosomal recessive disorder
• Accumulation of branched-chain amino acids and their
corresponding ketoacids in the blood, urine, and CSF
• Neonatal screening: modified Guthrie’s test (metabolic inhibitor to
B. subtilis – 4 azaleucine)
ISOVALERIC ACIDEMIA • Autosomal recessive metabolic disorder
• Low levels of isovaleryl-CoA dehydrogenase
• Leucine is not metabolized
• Mutations in the isovaleryl CoA dehydrogenase ( IVD) gene
• “sweaty feet” odor of urine.
• Cause CNS problems
• Treatment: restrict diet of protein, glycine and carnitine intake.
Homocystinuria • Autosomal recessive disorder of amino acid metabolism
• Lack of enzyme: cystathionine-Beta synthetase → required for
methionine metabolism
• Increased methionine and homocysteine
• Associated with osteoperosis, dislocated lenses in the eye (collagen
deficiency), mental retardation
• Treatment: restrict methionine in diet, vitamin B6 supplementation,
& trimethylglycine, folic acid supplementation, cysteine
(sometimes).
• Guthrie’s test using L-methionine sulfoximine as metabolic inhibitor.
Cystinuria • Inherited autosomal recessive
• Amino acid transport system defect
• Inadequate reabsorption of cysteine during the filtering process in
the kidneys.
• Urine: formation of precipitates → stone formation in the urinary
tract
• Hematuria, pain in the side, UTI.
• Treatment: increase urine volume to reduce concentration of
cysteine (increased water consumption)
• Cyanide nitroprusside test → red purple color reaction with
sulfhydryl groups.
• Quantitative: Ion exchange chromatography
METHODS OF AMINO • Fasting: 6 – 8 hours
ACID ANALYSIS • Heparinized plasma
• Deproteinization → performed within 30 minutes of sample
collection and analysis should be performed immediately or the
sample frozen @ -200C to 400C.
• Quantitative urinary amino acid analysis: 24 hour urine sample
preserved in thymol or organic solvents is required.
• Screening test: Thin layer chromatography
• Quantification: Ion exchange chromatography, HPLC reversed-phase
system equipped with fluorescence detection or capillary
electrophoresis.
• MS/MS: highly sensitive
