Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 amino acids.

It is a non-essential amino acid and it is found in large quantities in casein. In fact, the word "tyrosine" is from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese.

The thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the colloid of the thyroid are derived from tyrosine. Tyrosine is also the precursor to the skin pigment melanin.

References

IUPAC-IUBMB Joint Commission on Biochemical Nomenclature (1983). Nomenclature and Symbolism for Amino Acids and Peptides. Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology. Retrieved on 2007-05-17.