Unit Converter
Tyrosine (Tyr)
(Aromatic Amino Acid - Precursor of Dopamine, Catecholamines, Thyroid Hormones & Melanin)
Synonyms
- L-Tyrosine
- Tyr
- 4-Hydroxyphenylalanine
- Aromatic amino acid
- Precursor of catecholamines
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Unit Conversions
Molecular Weight of Tyrosine = 181.19 g/mol
µmol/L → mg/L
1 µmol/L=0.181 mg/L1\ \text{µmol/L} = 0.181\ \text{mg/L}1 µmol/L=0.181 mg/L 1 mg/L=5.52 µmol/L1\ \text{mg/L} = 5.52\ \text{µmol/L}1 mg/L=5.52 µmol/L
mg/dL → mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
µg/mL ↔ mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
mg/100 mL = mg% = mg/dL
Description
Tyrosine is a non-essential aromatic amino acid synthesized from phenylalanine, although adequate dietary phenylalanine is required.
It is a biochemical precursor for:
- Dopamine
- Norepinephrine & Epinephrine (catecholamines)
- Thyroid hormones (T3 & T4)
- Melanin
- Coenzyme Q10
- Protein synthesis
Tyrosine levels reflect:
- Amino-acid metabolism
- Liver function
- Inherited metabolic disorders
Physiological Role
1. Neurotransmitter Synthesis
Tyrosine → L-DOPA → Dopamine → Epinephrine/Norepinephrine
Critical for attention, stress response, autonomic regulation.
2. Thyroid Hormone Synthesis
Iodination of tyrosine residues in thyroglobulin → T4/T3.
3. Melanin Production
Tyrosinase converts tyrosine to melanin in melanocytes.
4. Growth & Protein Metabolism
Component of structural and enzymatic proteins.
Clinical Significance
ELEVATED TYROSINE (Tyrosinemia / Hyper-tyrosinemia)
1. Tyrosinemia Type I (FAH deficiency) - most severe
- Liver failure
- Hypophosphatemic rickets
- High AFP
- Risk of hepatocellular carcinoma
- Succinylacetone ↑↑ (diagnostic)
2. Tyrosinemia Type II (Tyrosine Aminotransferase deficiency)
- Corneal ulcers
- Painful keratitis
- Palmoplantar hyperkeratosis
3. Tyrosinemia Type III (HPD deficiency)
- Neurological symptoms
- Ataxia
- Mental delay
4. Transient Tyrosinemia of the Newborn
Due to immature liver enzymes (common, benign).
5. Liver Disease
Tyrosine elevation due to reduced metabolism.
6. Vitamin B6 Deficiency
Affects transamination pathways.
7. High Protein Intake / Supplementation
8. Prematurity
Immature hepatic metabolism.
LOW TYROSINE
1. Phenylketonuria
Phenylalanine cannot be converted to tyrosine → tyrosine deficiency.
2. Malnutrition
Low protein intake.
3. Malabsorption
Celiac disease, IBD, pancreatic insufficiency.
4. Severe Liver Disease
Impaired amino-acid interconversion.
5. Homogentisate Oxidase Excess (rare metabolic changes)
Low tyrosine may impair catecholamine synthesis → fatigue, low stress tolerance (research-based).
Reference Intervals
(Tietz 8E + Mayo + ARUP)
Plasma Tyrosine
- 30 – 120 µmol/L
(= 5.5 – 22 mg/L)
Newborns
- Often higher: 60 – 200 µmol/L, especially in premature infants.
Urine Tyrosine
Used in metabolic disorder screening
Diagnostic Uses
1. Screening for Tyrosinemias (Types I, II, III)
Elevated tyrosine ± succinylacetone.
2. Monitoring PKU Therapy
PKU patients require tyrosine supplementation → monitoring needed.
3. Newborn Screening Programs
Detects:
- FAH deficiency (Type I)
- Other amino-acid metabolic defects
4. Liver Disease Assessment
Tyrosine increases in hepatic dysfunction.
5. Nutritional Assessment
Part of amino-acid profile in malnutrition.
6. Neurological/Developmental Evaluation
Amino-acid disturbances in metabolic disorders.
Analytical Notes
- Fasting plasma sample recommended.
- Avoid hemolysis; RBCs contribute amino acids.
- Deproteinize sample promptly (stability issue).
- LC-MS/MS is gold standard; HPLC widely used.
- Tyrosine increases post-meal (protein intake).
- Use succinylacetone for definitive Tyrosinemia I diagnosis.
Clinical Pearls
- High tyrosine in a newborn does NOT confirm Tyrosinemia Type I → must check succinylacetone.
- PKU → high phenylalanine + low tyrosine pattern.
- Tyrosinemia II causes characteristic eye lesions + palmoplantar keratoderma.
- Plasma tyrosine can be transiently elevated in sick or premature neonates.
- Tyrosine is directly involved in thyroid hormone formation and catecholamine synthesis.
Interesting Fact
Tyrosine was named after “tyros” (Greek for cheese) because it was first isolated from casein in 1846 - long before its role in neurotransmitters and hormones was known.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acids
- Mayo Clinic Laboratories - Amino Acid Profile
- ARUP Consult - Amino Acid Analysis
- Inborn Errors of Metabolism Guidelines (ACMG)
- NIH / MedlinePlus - Amino Acid Tests
- WHO - Neonatal Screening Recommendations