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Asparagine (Asn)
(L-Asparagine – Neutral Amino Acid – Protein & Nitrogen Metabolism)
Synonyms
- Asparagine
- L-Asparagine
- Asn
- 2-Aminosuccinamic acid
- Neutral amino acid (amide group)
Units of Measurement
µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL
Description
Asparagine is a non-essential neutral amino acid formed from aspartate and ammonia via asparagine synthetase.
It plays a role in:
- Protein synthesis
- Nitrogen transport and storage
- CNS function
- Glycoprotein synthesis
- Ammonia detoxification
Plasma asparagine is measured as part of quantitative amino acid analysis for diagnosing:
- Asparagine synthetase deficiency
- Urea cycle disorders
- Aminoacidopathies
- Malnutrition and critical illness
- Leukemia therapy monitoring (L-asparaginase)
Physiological Role
1. Protein Building Block
Incorporated into proteins and peptides; abundant in CNS proteins.
2. Nitrogen Reservoir
Serves as a storage form of nitrogen for metabolic reactions.
3. Precursor for Aspartate
Through deamidation → helps generate metabolic intermediates.
4. Glycoprotein Synthesis
Needed for N-linked glycosylation → crucial for cell signaling & immunity.
5. Brain Function
Important in neuronal growth and neurotransmitter regulation.
Clinical Significance
Elevated Asparagine
1. Urea Cycle Disorders (UCD)
Mild to moderate increases occur due to altered nitrogen handling.
2. Hepatic Failure
Decreased ammonia detoxification → altered amino acid patterns.
3. Renal Dysfunction
Reduced clearance increases some neutral amino acids.
4. High-protein Nutrition / TPN
Low Asparagine
1. Asparagine Synthetase Deficiency (ASNS Deficiency)
Rare but severe:
- Microcephaly
- Seizures
- Global developmental delay
- Extremely low plasma asparagine
2. L-Asparaginase Therapy (ALL Treatment)
Used in acute lymphoblastic leukemia (ALL).
The enzyme depletes asparagine → essential for leukemic cell death.
3. Malnutrition / Catabolic States
Seen in:
- Severe protein deficiency
- Sepsis
- Trauma
- Critical illness
4. Mitochondrial or Organic Acid Disorders
Due to disrupted amino acid metabolism.
Reference Intervals
(Tietz 8E + Mayo Clinic LC-MS/MS + IFCC)
Fasting plasma values:
Adults
- 30 – 80 µmol/L
- ≈ 4.5 – 12 mg/L
Children & Infants
- Slightly higher values due to growth demands.
ASNS deficiency
- Often < 5–10 µmol/L
Unit Meanings
| Unit | Meaning |
| µmol/L | micromole per liter |
| mg/L | milligram per liter |
| mg/dL | milligram per deciliter |
| mg/100 mL | mg% (same as mg/dL) |
| mg% | milligram per 100 mL |
| µg/mL | microgram per milliliter |
1. Evaluation of Aminoacidopathies
Low Asn suggests asparagine synthetase deficiency.
Altered patterns help suggest:
- Urea cycle disorders
- Organic acidemias
- Liver failure
2. Monitoring L-Asparaginase Therapy
Used in oncology for:
- Acute lymphoblastic leukemia (ALL)
- Lymphoblastic lymphoma
Asparaginase → Asparagine depletion → therapeutic effect.
3. Nutritional Assessment
Low levels imply inadequate protein intake or catabolic stress.
4. Critical Care Evaluation
Amino acid imbalance reflects metabolic stress, sepsis, trauma.
Analytical Notes
- Preferred sample: fasting plasma (EDTA)
- Process immediately; store frozen for stability
- LC–MS/MS gives most accurate values
- Hemolysis can falsely increase levels due to erythrocyte content
Clinical Pearls
- L-Asparaginase fully depletes plasma asparagine, making it lethal to leukemic lymphoblasts.
- Very low asparagine with seizures + microcephaly → suspect ASNS deficiency.
- Asparagine is a non-essential amino acid, but becomes conditionally essential in illness.
- Interpretation must consider patterns with glutamine, aspartate, citrulline, and ornithine.
Interesting Fact
Asparagine was the first amino acid ever isolated (from asparagus juice in 1806). Its discovery laid the foundation for modern amino acid chemistry.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Amino Acids.
- Mayo Clinic Laboratories - Quantitative Amino Acid Panel.
- ARUP Consult - Amino Acidopathy Diagnostic Guide.
- IFCC Standardization of Amino Acid Methods.
- NIH / MedlinePlus - Amino Acid Overview.
- Genetics Literature - Asparagine Synthetase Deficiency.
- Oncology Guidelines - L-Asparaginase Monitoring.