Unit Converter
Proline (Pro)
(Non-Essential Amino Acid — Key in Collagen Synthesis, Wound Healing & Metabolic Pathway Disorders)
Synonyms
- Proline
- L-Proline
- Pro
- Pyrrolidine-2-carboxylic acid
- Amino acid: Pro
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Molecular Weight
115.13 g/mol
Key Unit Conversions
Mass ↔ Molar
1 mg/L=8.68 µmol/L1\ \text{mg/L} = 8.68\ \text{µmol/L}1 mg/L=8.68 µmol/L 1 µmol/L=0.115 mg/L1\ \text{µmol/L} = 0.115\ \text{mg/L}1 µmol/L=0.115 mg/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
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
mg%
\text{mg%} = \text{mg/dL}
Description
Proline is a non-essential, cyclic amino acid with a unique pyrrolidine ring that plays a major structural role in proteins—especially collagen, where it constitutes nearly 25% of the amino-acid composition.
Proline is vital for:
- Collagen stabilization (via hydroxyproline → triple helix)
- Wound healing
- Skin, tendon, bone, and connective-tissue integrity
- Redox balance (converted to pyrroline-5-carboxylate, P5C)
- Energy supply to rapidly dividing tissues
Its metabolism is tightly linked with ornithine, glutamate, and P5C, and disorders can cause significant neurological or metabolic disease.
Physiological Role
- Major component of collagen & extracellular matrix
- Supports skin healing, bone formation
- Involved in antioxidant pathways
- Stabilizes protein structure (kinks in peptide chains)
- Intermediate in nitrogen metabolism
- Supports fetal growth and immune function
Clinical Significance
HIGH Proline (Hyperprolinemia)
Occurs mainly in:
1. Hyperprolinemia Type I
- Defect: PRODH (proline oxidase)
- Mild/moderate elevation
- Usually asymptomatic
- Occasional seizures, developmental delay
2. Hyperprolinemia Type II
- Defect: ALDH4A1 (P5C dehydrogenase)
- Higher levels
- Seizures, recurrent metabolic crises
- Mental retardation
- Schizophrenia association (reported)
3. Liver Disease
Reduced metabolism → mild elevation.
4. Renal Failure
Reduced clearance → elevated amino acids.
5. High-proline diet / supplementation
LOW Proline (Rare)
Seen in:
- Malnutrition
- Malabsorption
- Severe liver disease
- Inborn errors of proline/glutamate metabolism
- Pregnancy (mild physiologic reduction)
Low levels typically have limited direct clinical impact, but reflect global amino-acid deficiency.
Reference Intervals
(Tietz 8E + Mayo + ARUP + ACMG metabolic panels)
Plasma Proline
- 150 – 450 µmol/L
(= 17 – 52 mg/L)
Newborns
- 100 – 350 µmol/L
Children
- 120 – 400 µmol/L
Hyperprolinemia “flags”
- > 600 µmol/L → investigate Type I
- > 1000 µmol/L → investigate Type II
Diagnostic Uses
1. Amino Acid Profile in Suspected Metabolic Disease
Especially:
- Seizures in infancy
- Developmental delay
- Metabolic acidosis
- Failure to thrive
- Psychiatric/behavioral disorders
2. Hyperprolinemia Evaluation
Proline is a primary marker.
3. Collagen Disorders
Not routinely used, but altered metabolism may be part of connective-tissue diseases.
4. Nutritional Assessment
Low levels reflect protein deficiency.
5. Mitochondrial Metabolism Evaluation
Linked with P5C, glutamate, and ornithine pathways.
Analytical Notes
- Plasma sample collected fasting
- Use heparin or EDTA
- Amino-acid profiling via HPLC or LC–MS/MS
- Hemolysis can alter results
- Specimen must be deproteinized quickly for accuracy
Clinical Pearls
- Hyperprolinemia type II causes higher proline + P5C → seizures & brain dysfunction.
- Mild hyperprolinemia may be incidental and benign.
- Proline metabolism closely interacts with ornithine & glutamate, so combined elevation patterns matter.
- Always interpret with full amino-acid panel.
- Levels vary with age, fasting state, and stress.
Interesting Fact
Proline is the only amino acid where the side chain bonds to the nitrogen of the amino group, forming a ring—this special structure helps stabilize collagen’s triple helix.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition — Amino Acids
- ACMG Guidelines — Amino Acid Disorders
- Mayo Clinic Laboratories — Plasma Amino Acid Profile
- ARUP Consult — Amino Acid Metabolism Tests
- NIH / MedlinePlus — Amino Acid Testing