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Clinical Chemistry (CC 1) > (M) Lec 5: Amino Acids (P1: Aminoacidopathies) > Flashcards

(M) Lec 5: Amino Acids (P1: Aminoacidopathies) Flashcards

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1
Q
  • These are the building blocks of proteins (100-150 of these = proteins)
  • The second most abundant NPN (second to urea)
A

Amino Acids

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2
Q

Amino Acids are called as such because of what 2 groups in their composition attached to Carbon?

A

Basic = Amino group (nitrogen-containing)
Acid = Carboxyl group

Note: They only vary in their side chains (R-group)

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3
Q

Conditions/disorders wherein an individual lacks certain enzymes which are important for the metabolism of amino acids

A

Aminoacidopathies (or elevated amino acid levels, in other words)

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4
Q

These amino acids cannot be synthesized by the body and therefore comes from the proteins that we eat

A

Essential Amino Acids

Ex.: Histidine, Leucine, Isoleucine, Arginine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine

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5
Q

These amino acids can be naturally synthesized by the body therefore dietary intake of these are not necessary

Ex.: Alanine, Asparagine, Aspartic Acid, Glutamic Acid, Selenocysteine, and Serine

A

Non-Essential Amino Acids

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6
Q

These amino acids are normally produced in a healthy individual however, there are infants who acquire inborn errors which manifest as aminoacidopathies leading to decreased amounts of this kind of amino acid

A

Semi-Essential (Conditionally Essential)

Ex.: Arginine, Cysteine, Glutamine, Glycine, Proline, and Tyrosine

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7
Q
  • Refers to inherited errors of metabolism caused by:
    1. A defective/deficient enzyme that inhibits the body’s ability to metabolize certain amino acids
    2. Abnormalities that exist either in the activity of a specific enzyme in the pathway or membrane transport system
A

Aminoacidopathies

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8
Q

Aminoacidopathies

If an individual lacks the phenylalanine hydroxylase enzyme, what will happen to the phenylalanine levels in the body (+ include the name of the condition)?

A

Phenylalanine will increase leading to Phenylketonuria

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9
Q

Aminoacidopathies

If an individual lacks the tyrosine aminotransferase enzyme, what condition will the person manifest?

A

Hereditary Type 2 Tyrosinemia

Tyrosine cannot be converted to 4HPP

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10
Q

Aminoacidopathies

Hereditary Type 3 Tyrosinemia occurs if there is a deficiency of what enzyme?

A

4HPP Dioxygenase

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11
Q

Aminoacidopathies

Homogentisate (HGA) will be converted to Maleylacetoacetate (MAA) with the help of what enzyme (+ include the condition)?

A

HGA Oxidase (alkaptonuria)

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12
Q

Aminoacidopathies

Maleylacetoacetate (MAA) will be converted to what using the MAA isomerase?

A

Fumarylacetoacetate (FAA)

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13
Q

Aminoacidopathies

Fumarylacetoacetate (FAA) will be degraded into what 2 compounds?

A
  1. Fumarate
  2. Acetoacetate
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14
Q

Aminoacidopathies

A lack of the FAA hydrolase produces what condition?

A

Hereditary Tyrosinemia Type 1

Most severe form

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15
Q

Aminoacidopathies

A deficiency of phenylalanine hydroxylase (PAH) which catalyzes the conversion of phenylalanine to tyrosine

A

Phenylketonuria

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16
Q

Aminoacidopathies

Phenylketonuria can also happen when there is a problem with what 2 substances? (aside from PAH)

A
  1. Tetrahydrobiopterin
  2. Dihydrobiopterin

Are co-enzymes (important for the reaction)

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17
Q

Aminoacidopathies

Patients are usually:
1. Normal at birth but manifest mental retardation at the 6th month
2. Decreased skin pigmentation, eczema, and musty odor in blood and urine

A

Phenylketonuria

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18
Q

Aminoacidopathies

A condition wherein tyrosine levels are decreased (important for oxidation, protein synthesis, catecholamine, thyroxine, and melanin-formation)

A

Phenylketonuria

19
Q

Diagnosing Phenylketonuria

  • Principle: Semiquantitive bacterial inhibition assay
  • Elevated phenylalanine levels facilitate the growth of B. subtilis in a culture medium with an inhibitor (beta-2-thienylalanine)
  • The inhibitor is no longer effective against bacteria
  • Can detect serum phenylalanine levels of 180-240 umol/L (3-4 mg/dL)
  • Positive Result: (+) growth of B. subtilis (elevated phenylalanine)
  • Prone to false (-) negative results
A

Guhtrie Test

20
Q

Diagnosing Phenylketonuria

  • Principle: Quantitative assay that directly measures phenylalanine in blood filter disks via immunofluorescence
  • It yields quantitative results, is more adaptable to automation, and is not affected by the presence of antibiotics
  • Based on fluorescence of a complex formed of phenylalanine-ninhydrin-copper in the presence of dipeptide
  • Any positive results must be verified
A

Microfluorimetric Assay

21
Q

Diagnosing Phenylketonuria

Familiarize yourself with the OTHER possible tests for phenylketonuria diagnosis (apart from the Guthrie Test and Microfluorimetric Assay)

A
  1. GC/MS
  2. Tandem Mass Spectrometry (the GOLD STANDARD)
  3. DNA Analysis

Tandem Mass Spectrometry: Compares both phenylalanine and tyrosine concentrations

22
Q

Aminoacidopathies

  • Inborn metabolic disorder of tyrosine catabolism (increased levels)
  • Excretion of tyrosine and tyrosine catabolites in urine
A

Tyrosinemia

23
Q

Types of Tyrosinemia

  • Most severe kind; a deficiency of fumarylacetoacetate hydrolase
  • Failure to thrive, diarrhea, vomiting, jaundice, cabbage-like odor, distended abdomen, swelling of legs, and increased predisposition for bleeding
  • Can lead to liver and kidney failure (Fanconi Syndrome), affects CNS, and increases risk of cirrhosis or liver cancer
A

Type 1

24
Q

Types of Tyrosinemia

  • A deficiency of tyrosine aminotransferase
  • Half are mentally retarded and have symptoms of excessive tearing, photophobia, eye pain and redness, and painful skin lesions on the palms and soles
A

Type 2

25
Q

Types of Tyrosinemia

  • A deficiency of 4-hydroxyphenylpyruvate dioxygenase (4HPP Dioxygenase)
  • Clinical presentation includes mild mental retardation, seizures, and periodic loss of balance and coordination
A

Type 3

A rare type

26
Q

Diagnosing Tyrosinemia

What tests can be employed?

A
  1. Tandem MS
  2. Mass Spectrometry
27
Q

Aminoacidopathies

  • A secondary deficiency of homogentisate oxidase (HGA is increased and will not be coverted to Maleylacetoacetate)
  • Urine turns brownish-black when mixed with air due to an accumulation of homogentisic acid (HGA) in the urine (when oxidized produces a dark pigment)
  • Onchronosis - pigmentations on different parts of the body such as:
  1. HGA accumulation and pigment
  2. Dark Spots on the sclera
  3. Deposition in cartilage
  4. Arthritis-like degeneration
A

Alkaptonuria

28
Q

Diagnosing Alkaptonuria

During urinalysis, the urine (with homogentisic acid) of the patient turns black upon the addition of what compound?

A

Ferric Chloride (FeCl2)

29
Q

Aminoacidopathies

  • Burnt sugar odor in the urine, breath, and skin
  • Deficiency of α-ketoacid decarboxylase
  • There is an accumulation of branched chain amino acids (leucine, isoleucine, and valine)
  • Normal at Birth → Lethargy, MR, and CNS symptoms
A

Maple Syrupe Urine Disorder

30
Q

Diagnosing MSUD

  • A neonatal screening test
  • B. subtilis in a culture media with 4-azaleucine as inhibitor
  • Positive result: (+) growth of B. subtilis
A

Modified Guthrie Test

Modified because a different inhibitor is used

31
Q

Diagnosing MSUD

  • 3 branched-chain amino acids uses filter paper specimen treated with a solvent mixture of methanol and acetone to denature the hemoglobin
  • Leucine dehydrogenase is added for the fluorescence of NADH
  • Leucine level above 4 mg/dL is indicative of MSUD
A

Microfluorimetric Assay

32
Q

Diagnosing MSUD

The gold standard test

A

Tandem MS

33
Q

Aminoacidopathies

  • Deficiency of isovaleryl-CoA dehydrogenase (preventing normal metabolism of leucine ONLY)
  • Sweaty feet odor and brain damage
  • Mild to moderate ketonuria, metabolic acidosis,
    hyperammonemia, thrombocytopenia, and neutropenia
A

Isovaleric Acidemia

34
Q

Diagnosing Isovaleric Acidemia

What is the gold standard and what is the common method? (2 answers)

A

Gold: Tandem MS
Common: Chromatography

35
Q

Aminoacidopathies

If chromatography is the common screening method performed by laboratories, Tandem MS is done by who?

A

Reference Labs

36
Q

Aminoacidopathies

  • Deficiency of cystathionine-βsynthetase (necessary for the metabolism of methionine, that results in elevated plasma and urine levels of methionine and its precursor, homocysteine)
  • Multisystemic connective tissue disorder (muscles and bones)
A

Homocystinuria

37
Q

Diagnosing Homocystinuria

  • B. subtilis in a culture media with L-methionine sulfoximine as an inhibitor
A

Modified Guthrie Test

38
Q

Diagnosing Homocystinuria

This screening test detects elevations in urinary total homocysteine which can be measured in high testing volumes and provide a rapid turn around by using liquid chromatography electrospray

A

Tandem MS

39
Q

Diagnosing Homocystinuria

  • This confirmatory test indicates that a methionine level greater than 2 mg/dL confirms a positive result
A

HPLC

40
Q

Aminoacidopathies

  • Defect in the amino acid transport system (no enzyme deficiency)
  • Inadequate renal reabsorption of cystine → renal stones/crystals
A

Cystinuria

41
Q

Diagnosing Cystinuria

  • Testing the urine for cystine using cyanide nitroprusside which produces a red-purple color upon reaction with sulfhydryl groups
  • False positive results as a result of homocysteine must be ruled out (Homocysteine, Lysine, Arginine, Ornithine)
A

Urine Test

42
Q

Amino Acid Analysis

Identify the sample:
- 6-8 hour fasting period (to remove the dietary effects of amino acids)
- Must come from a heparin tube and be separated immediately with no blood cells

A

Plasma

43
Q

Amino Acid Analysis

Identify the sample:
- A random specimen is allowed for screening purposes
- For quantification purposes, a 24-hour period of collecting this sample is preserved with thymol or organic solvent
- Amniotic fluid may also be analyzed (for inborn errors)

A

Urine

44
Q

Amino Acid Analysis

Familiarize with the 3 methods in analysis

A
  1. Liquid Chromatography - Method of Choice
  2. Ion Exchange Chromatography - for quantification
  3. Mass Spectrometry

Clinical Chemistry (CC 1) (22 decks)

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