L-Arginine

L‑Arginine is a semi‑essential, protein‑derived amino acid that serves as a substrate for multiple metabolic pathways. In humans it is most renowned for being the primary precursor for nitric‑oxide (NO) synthesis, a signaling molecule that regulates vascular tone, immune function, and cellular metabolism.

L‑Arginine (L‑2‑amino‑5‑guanidino‑pentanoic acid) has the molecular formula C₆H₁₄N₄O₂ and a molecular weight of 174.20 g·mol⁻¹. The IUPAC name is (2S)-2-amino-5-(guanidinium)pentanoic acid. It is a basic, polar amino acid with a side‑chain containing a guanidinium group (pKa ≈ 12.5) that confers a permanent positive charge at physiological pH, facilitating interaction with negatively charged cellular components. The α‑amino group and carboxyl group make it zwitterionic in neutral solutions. L‑Arginine is highly soluble in water (≈1 g/mL at 25 °C) and forms crystalline white powders. Its optical activity is defined by the L‑configuration (S‑enantiomer), which is the biologically active form in humans.

Natural dietary sources include red meat, poultry, fish, dairy, nuts, and seeds; typical diets supply 2–5 g/day. Commercially, L‑arginine is produced by microbial fermentation (e.g., Corynebacterium glutamicum) or via chemical synthesis from L‑ornithine. Fermentation yields a high‑purity (>99 %) product with minimal contaminants, preferred for pharmaceutical‑grade supplements. Extraction from plant proteins (e.g., soy) is less common due to lower yield. Quality considerations include verification of the L‑enantiomer, absence of heavy metals, and compliance with GMP (Good Manufacturing Practice) standards. Certificate of analysis (CoA), third‑party testing (e.g., USP, NSF), and stability testing (e.g., moisture content, degradation under humidity) are critical for ensuring product potency and safety.