L-Tyrosine

**Semantic type:** Amino Acid, Peptide, or Protein

**Definition:** The levorotatory isomer of the aromatic amino acid tyrosine. L-tyrosine is a naturally occurring tyrosine and is synthesized in vivo from L-phenylalanine. It is considered a non-essential amino acid; however, in patients with phenylketonuria who lack phenylalanine hydroxylase and cannot convert phenylalanine into tyrosine, it is considered an essential nutrient. In vivo, tyrosine plays a role in protein synthesis and serves as a precursor for the synthesis of catecholamines, thyroxine, and melanin.

**Synonyms:** - (S)-2-Amino-3-(4-hydroxy-phenyl)propanoic acid - L-Phenylalanine, 4-hydroxy- - TYR - TYROSINE - TYROSINE, (L) - Tyr - Tyrosine - Tyrosine