Unit Converter
Isopropanol
Synonyms
- Isoleucine
- L-Isoleucine
- Ile
- Branched-chain amino acid (BCAA)
- Plasma isoleucine
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Molecular Weight
Isoleucine ≈ 131.17 g/mol
Key Unit Conversions
1 mg/L = 7.63 µmol/L
1 mg/dL = 76.3 µmol/L
1 µg/mL = 1 mg/L
1 µmol/L = 0.131 mg/L
mg/dL = mg% = mg/100 mL
Description
Isoleucine is an essential branched-chain amino acid (BCAA), along with:
- Leucine
- Valine
It plays central roles in:
- Muscle energy metabolism
- Protein synthesis
- Glucose regulation
- Ketogenesis and gluconeogenesis
Isoleucine is obtained exclusively from diet-particularly protein-rich foods.
Physiological Role
1. Muscle Energy & Protein Synthesis
- Major substrate for skeletal muscle
- Important during exercise and fasting
2. Glucose Metabolism
Isoleucine is both ketogenic and glucogenic, producing:
- Acetyl-CoA
- Succinyl-CoA
3. Immune Function
Supports lymphocyte proliferation and cytokine balance.
4. Brain & Nervous System
BCAAs compete with aromatic amino acids for transport across the blood–brain barrier.
5. Growth & Development
Essential for infants and children for normal protein synthesis.
Clinical Significance
HIGH Isoleucine (Hyperisoleucinemia)
1. Maple Syrup Urine Disease (MSUD)
Most important cause.
Features:
- Deficiency of branched-chain α-ketoacid dehydrogenase (BCKD)
- Increased: isoleucine, leucine (highest), valine
- Sweet “maple syrup” urine odor
- Poor feeding, lethargy, seizures
Plasma levels often:
- Isoleucine > 400–800 µmol/L
- Leucine usually highest (>1000 µmol/L)
2. Liver Disease
Impaired amino-acid metabolism.
3. High-Protein Intake / TPN
Supplement-induced rise.
4. Inborn Errors of Metabolism
BCAA transport disorders or hepatic enzyme defects.
5. Renal Failure
Reduced clearance of amino acids.
LOW Isoleucine (Hypoisoleucinemia)
Causes:
- Malnutrition
- Malabsorption (celiac disease, IBD)
- Long-term parenteral nutrition without adequate AA balance
- Chronic liver disease
- BCAA catabolic upregulation (critical illness)
- Hypercatabolic states: sepsis, trauma, burns
Clinical Effects:
- Muscle weakness
- Fatigue
- Growth delay in children
- Immune dysfunction
Reference Intervals
Plasma Isoleucine
- Adults: 40 – 120 µmol/L
- Newborns & infants: 30 – 150 µmol/L
- Children: 40 – 130 µmol/L
MSUD Diagnostic Levels
- >400 µmol/L → suspicious
- >800 µmol/L → highly suggestive when with high leucine & valine
- Must always interpret with leucine, valine, alloisoleucine.
Diagnostic Uses
1. Screening for Maple Syrup Urine Disease (MSUD)
One of the classical amino acid findings:
- Isoleucine ↑
- Leucine ↑↑↑
- Valine ↑
2. Plasma Amino Acid Profiling
Used for:
- Inborn errors of metabolism
- Liver disease
- Renal dysfunction
- Nutritional assessment
3. Monitoring BCAA Therapy
In MSUD, TPN, or metabolic crisis.
4. Critical Illness Assessment
Low isoleucine correlates with catabolism.
5. Sports Medicine & Nutrition
BCAA supplementation monitoring (research use).
Analytical Notes
- Fasting sample preferred
- Transport on ice if delayed
- Plasma (lithium heparin) or serum acceptable
- Must be deproteinized for HPLC/LC-MS/MS
- Alloisoleucine is pathognomonic for MSUD
- Avoid sample hemolysis
Clinical Pearls
- In MSUD, alloisoleucine elevation is the most specific finding.
- BCAAs compete with tryptophan for brain entry - low isoleucine may affect neurotransmission.
- Critical illness often produces BCAA depletion, not elevation.
- Low isoleucine is common in strict vegetarian diets without adequate protein.
Interesting Fact
Isoleucine is one of the three branched-chain amino acids, responsible for nearly 35% of essential amino acids in muscle protein.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acids.
- ACMG Guidelines - Aminoacidopathies & MSUD.
- Mayo Clinic Laboratories - Plasma Amino Acids.
- ARUP Consult - Inborn Errors of Metabolism.
- NIH / MedlinePlus - Amino Acid Testing.
- UpToDate - Evaluation of Maple Syrup Urine Disease.