Leucine

Leucine is an essential branched‑chain amino acid (BCAA) that cannot be synthesized by humans and must be obtained from the diet. It is a key building block of proteins and serves as a primary signal for muscle protein synthesis, making it a central nutrient for maintaining and building lean tissue.

• Molecular Formula and Weight: Leucine (L‑leucine) is a non‑polar, essential α‑amino acid with the molecular formula C₆H₁₃NO₂ and a molecular weight of 131.17 g·mol⁻¹.
• IUPAC Name: Its IUPAC name is (2S)-2‑amino‑4‑methylpentanoic acid.
• Side Chain: The side chain consists of an isobutyl group (–CH₂‑CH(CH₃)₂) attached to the α‑carbon, conferring its characteristic branched‑chain structure.
• Zwitterion Form: At physiological pH (~7.4) leucine exists as a zwitterion (–NH₃⁺ and –COO⁻).
• Solubility: The amino acid is moderately soluble in water (≈22 g/L at 25 °C) and highly soluble in ethanol and methanol.
• Optical Activity: Its optical activity (L‑configuration) is the biologically active form used in protein synthesis.
• Functional Roles: The side‑chain hydrophobicity contributes to its role as a key regulator of the mTOR pathway, while the α‑amino group participates in peptide bond formation.

• Dietary Sources: Dietary leucine is abundant in animal proteins (e.g., whey, chicken, beef, fish) and in plant sources such as soy, lentils, and peanuts.
• Commercial Production: Commercially, leucine is typically produced by microbial fermentation (e.g., Corynebacterium glutamicum or E. coli engineered strains) followed by crystallization, yielding a high‑purity (>98 %) free‑form amino acid.
• Alternative Synthesis: Chemical synthesis via the Strecker or reductive amination pathways is also employed, though fermentation is preferred for food‑grade products due to lower impurity risk.
• Supplement Quality: For supplements, manufacturers must verify identity and purity through HPLC, assess for heavy‑metal contamination, and ensure compliance with USP or EFSA standards.
• Third-Party Certifications: Look for third‑party certifications (e.g., NSF, Informed‑Choice) to guarantee consistent quality and minimal adulteration.