L-Citrulline - Key Amino Acid for Nitric Oxide and Urea Cycle

L-Citrulline: Biochemical Significance and Industrial Applications

1. Definition and General Description

L-Citrulline (English: L-Citrulline, German: L-Citrullin) is a naturally occurring α-amino acid that is not incorporated into proteins but participates in the urea cycle. It was first discovered in watermelon (Citrullus vulgaris).

CAS: 372-75-8

Synonyms: L-Citrulline, (S)-2-Amino-5-ureidopentanoic acid

2. Molecular Formula and Structure

Molecular formula: C₆H₁₃N₃O₃

Structure: Contains an α-amino group and a urea functional group (-NH-CO-NH₂) on the side chain.

3. Physicochemical Properties

Appearance: White crystalline powder.

Odor: Practically odorless.

Density: ~1.40 g/cm³ (at 20°C).

Melting point: ~214–218°C (with decomposition).

Boiling point: Decomposition occurs before reaching the classical boiling point.

Flash point: Not typically applicable for such amino acids, due to decomposition at high temperatures.

Solubility:

• In water: Readily soluble.

• In ethanol and other organic solvents: Low solubility.

Decomposition: Upon heating above 200°C, decarboxylation and decomposition processes may occur with the release of ammonia and other by-products.

Storage conditions: Store in a dry, cool place, tightly sealed, protected from direct light.

Stability: Sufficiently stable at room temperature and normal humidity conditions.

4. Potential Impact and Safety

On the organism: Considered non-toxic at recommended dosages. Improves nitrogen metabolism; commonly used by athletes and patients with urea cycle disorders.

Environmental aspect: Does not have significant pollutant potential; readily biodegradable.

5. Use and Applications

Dietary supplements: Used in sports supplements to reduce fatigue, improve blood flow, and enhance endurance.

Medical research: Studied in the context of cardiovascular diseases, erectile dysfunction, and vascular issues.

Pharmaceuticals: Included in complex preparations to support the urea cycle and nitric oxide synthesis.

Agrochemistry (rare): May be included in some metabolic test systems for diagnosing urea cycle enzyme function.

6. Conclusion

L-Citrulline (CAS 372-75-8) is an important biogenic amino acid that, although not part of the proteinogenic set, plays a key role in nitrogen metabolism. It is used in dietary supplements, sports nutrition, and medicine, with a good safety profile when properly stored and used.