Methionine (Met)

Unit Converter
Methionine (Met)

Synonym

2-amino-4-(methylthio)butanoic acid

Units of measurement

µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL

(Essential Sulfur-Containing Amino Acid — Key for Methylation, SAM Formation & Inborn Errors of Metabolism)

Synonyms

Methionine
L-Methionine
Met
2-Amino-4-(methylthio)butanoic acid
Sulfur amino acid

Units of Measurement

µmol/L
mg/L
mg/dL
mg/100 mL
mg%
µg/mL

Unit Conversions

Molecular Weight of Methionine = 149.21 g/mol

µmol/L ↔ mg/L

1 µmol/L=0.149 mg/L1\, \text{µmol/L} = 0.149\, \text{mg/L}1µmol/L=0.149mg/L 1 mg/L=6.70 µmol/L1\, \text{mg/L} = 6.70\, \text{µmol/L}1mg/L=6.70µmol/L

mg/dL → mg/L

1 mg/dL=10 mg/L1\, \text{mg/dL} = 10\, \text{mg/L}1mg/dL=10mg/L

mg% = mg/dL

µg/mL → mg/L

1 µg/mL=1 mg/L1\, \text{µg/mL} = 1\, \text{mg/L}1µg/mL=1mg/L

Description

Methionine is an essential amino acid that must be obtained from the diet.
It plays a central role in:

Methylation reactions
Formation of S-adenosylmethionine (SAM) – the universal methyl donor
Synthesis of cysteine, glutathione & taurine
Transsulfuration pathway
Protein synthesis & one-carbon metabolism

In clinical labs, methionine is measured as part of plasma amino-acid profiling, especially when evaluating metabolic disorders in newborns and children.

Physiological Role

1. SAM Cycle (Methylation)

Methionine → SAM → SAH → Homocysteine → Methionine
Regulates:

DNA methylation
Neurotransmitter synthesis
Phospholipid metabolism

2. Transsulfuration

Methionine is a precursor to:

Cysteine
Glutathione (major antioxidant)
Taurine

3. Growth & Protein Synthesis

Needed for normal hepatic and muscle protein formation.

Clinical Significance

HIGH METHIONINE (Hyper-methioninemia)

Causes:

1. Genetic Disorders (Major Clinical Focus)

MAT I/III deficiency (Methionine adenosyltransferase deficiency)
Cystathionine β-synthase (CBS) deficiency (homocystinuria)
Glycine N-methyltransferase deficiency (GNMT deficiency)
S-adenosylhomocysteine hydrolase deficiency

These disorders present in infancy or childhood.

2. Liver Disease

Acute or chronic hepatitis
Cirrhosis
Impaired transamination

3. Parenteral Nutrition (TPN)

High amino-acid infusion.

4. Premature Infants

Immature metabolic pathways → transient elevation.

5. Vitamin B6, B12 or Folate Deficiency

Impaired remethylation or transsulfuration.

6. Methionine Loading

After oral load for metabolic stress tests.

Symptoms of High Methionine

Lethargy
Developmental delay
Liver dysfunction
Odor of “cabbage-like breath” (in severe hypermethioninemia)
Possible neurological issues depending on enzyme defect

LOW METHIONINE (Hypo-methioninemia)

Causes

Malnutrition / protein deficiency
Malabsorption
Chronic liver disease
Severe illness / sepsis
Homocystinuria with loss into alternate pathways
SAM cycle disorders
Diets deficient in sulfur amino acids

Symptoms

Usually subtle; may relate to:

Poor growth
Low muscle mass
Low glutathione (poor antioxidant capacity)
Fatigue

Reference Intervals

(Tietz 8E + Mayo + ARUP + ACMG metabolic reference ranges)

Plasma Methionine

Age Group	Reference Interval
Adults	10 – 40 µmol/L
Children	12 – 45 µmol/L
Newborns	15 – 70 µmol/L (higher due to immature pathways)

Clinical Significance Thresholds

> 80 µmol/L → hypermethioninemia; evaluate liver/metabolic disorders
> 200–300 µmol/L → consider MAT I/III deficiency
> 500 µmol/L → severe metabolic disease (CBS or SAH hydrolase deficiency)

Units Description

µmol/L

Preferred unit for amino-acid testing.

mg/L / µg/mL

Mass concentrations calculated using MW.

mg/dL, mg%

Older units, still convertible.

Diagnostic Uses

1. Inborn Errors of Methionine Metabolism

MAT I/III deficiency
Homocystinuria (CBS deficiency)
GNMT deficiency
SAH hydrolase deficiency

2. Liver Function Evaluation

Methionine elevation is sensitive to hepatic dysfunction.

3. Nutritional Status Assessment

Especially in TPN patients.

4. Investigation of Neurological Disorders

Some metabolic defects cause progressive neurological disease.

5. Monitoring Therapy

Pyridoxine (B6) for CBS deficiency
Methionine restriction diets
SAM cycle interventions

Analytical Notes

Fasting sample recommended
Avoid hemolysis (releases intracellular amino acids)
Plasma should be deproteinized or frozen promptly
Measured by HPLC or LC–MS/MS
Newborn screening detects methionine elevation via tandem MS/MS

Clinical Pearls

Elevated methionine in a newborn is a red flag for homocystinuria or MAT deficiency.
Always interpret methionine together with homocysteine, cysteine, SAM/SAH if available.
In liver disease, methionine rises earlier than AST/ALT abnormalities.
Severe hypermethioninemia may produce a “cabbage odor” due to volatile sulfur compounds.
Methionine restriction diet + B6 therapy can normalize methionine in some conditions.

Interesting Fact

Methionine is the first amino acid inserted during protein synthesis in all eukaryotic and prokaryotic systems (start codon AUG → Met).

SEO Unit Converter Text

Methionine converter — convert between µmol/L, mg/L, mg%, and µg/mL with interpretation for metabolic disorders, newborn screening, and liver disease.

References

Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition — Amino Acids
ACMG Guidelines for Metabolic Disorders & Newborn Screening
Mayo Clinic Laboratories — Plasma Amino Acids
ARUP Consult — Amino Acid Interpretation
NIH / MedlinePlus — Methionine
NEJM — Hyperhomocysteinemia & Sulfur Amino Acid Disorders

Unit ConverterMethionine (Met)

METHIONINE (Met)