L-Tyrosine Fatigue

L‑Tyrosine is a conditionally essential, aromatic amino acid that serves as a direct precursor for catecholamine neurotransmitters (dopamine, norepinephrine, epinephrine) and thyroid hormones. In the context of fatigue, supplemental L‑tyrosine is used to sustain neurotransmitter synthesis and support cognitive and physical performance when the body is under acute stress, sleep deprivation, or prolonged mental work.

• IUPAC name: (2S)-2‑amino‑3‑(4‑hydroxyphenyl)propanoic acid.
• Molecular formula: C₉H₁₁NO₃.
• Molar mass: 181.19 g mol⁻¹.
• Structure: A phenolic aromatic ring (para‑hydroxyl) attached to a β‑amino‑acid backbone; the para‑hydroxyl group confers moderate polarity (log P ≈ −0.5) and enables hydrogen‑bonding. L‑Tyrosine is a zwitterion at physiological pH (pKa₁ ≈ 2.2 for carboxyl, pKa₂ ≈ 9.1 for amino). It is water‑soluble (≈1 g · 100 mL⁻¹ at 25 °C) and stable under neutral pH, but prone to oxidation at the phenolic group, requiring antioxidant protection in formulations.

• Natural L‑tyrosine is abundant in protein‑rich foods (e.g., soy, cheese, turkey) and is extracted from hydrolyzed protein sources (e.g., whey, soy isolate) via enzymatic hydrolysis, followed by crystallization.
• Industrially, it is also produced by microbial fermentation (e.g., E. coli engineered to over‑produce L‑tyrosine) and then purified by ion‑exchange chromatography.
• High‑purity (>99 %) pharmaceutical‑grade L‑tyrosine is typically obtained through a combination of fermentation and crystallization, ensuring low heavy‑metal and microbial contamination.
• For supplements, Good Manufacturing Practice (GMP) certification, third‑party testing (e.g., USP, NSF), and verification of absence of residual solvents are key quality markers.