Arginine

L‑arginine is a semi‑essential, protein‑building amino acid that serves as a precursor for nitric‑oxide (NO) synthesis and several other bioactive molecules. It is most widely recognized for its role in vascular tone regulation and as a substrate for the urea cycle, helping to remove ammonia from the body.

• Molecular Formula and Weight: L‑Arginine (L‑2‑amino‑5‑guanidino‑pentanoic acid) has the molecular formula C₆H₁₄N₄O₂ and a molecular weight of 174.20 g·mol⁻¹.
• IUPAC Name: IUPAC name: (2S)-2‑amino‑5‑(guanidino)pentanoic acid.
• Structure: Its structure comprises a α‑amino acid backbone (α‑carboxyl and α‑amino groups) plus a side‑chain guanidinium group (–C(=NH)NH₂) that is positively charged at physiological pH, giving the molecule a high pKa (~12.5).
• Guanidinium Moiety: The guanidinium moiety is responsible for its high basicity and ability to donate nitrogen in the urea cycle.
• Properties: L‑arginine is water‑soluble, stable at neutral pH, and readily oxidized by nitric‑oxide synthase to L‑citrulline.
• Transport: Its zwitterionic nature facilitates transport via cationic amino‑acid transporters (e.g., CAT‑1) across cell membranes.

• Production: Commercial L‑arginine is typically produced by microbial fermentation (e.g., Corynebacterium glutamicum) or by chemical synthesis from L‑glutamic acid.
• Dietary Sources: Natural dietary sources include red meat, poultry, fish, dairy, nuts (especially peanuts), and seeds (e.g., pumpkin, sesame).
• Supplement Production: For supplements, high‑purity (>98 %) L‑arginine is obtained via crystallization and recrystallization steps to remove impurities and endotoxins.
• Quality Control: Quality‑focused manufacturers employ GMP‑compliant fermentation and rigorous testing (e.g., HPLC, mass spectrometry) to ensure identity, potency, and absence of heavy metals or microbial contaminants.
• Product Selection: When selecting a product, look for third‑party testing (e.g., USP, NSF) and a label indicating “L‑arginine hydrochloride” or “free‑form L‑arginine” for optimal bioavailability.