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Tyrosine is a nonessential amino acid with the chemical formula C9H11NO3. It is produced in the body from phenylalanine and is a precursor of melanin and of several neurotransmitters and hormones, such as epinephrine and thyroxine[1].


The German chemist Justus Freiherr von Liebig discovered[2] tyrosine in 1846 while experimenting with cheese. In his 1846 publication the extraction process was described as below:

  • Crude casein was mixed with equal amounts of potassium hydroxide.
  • Hot water and acetic acid were then added to the resultant mass.
  • Upon cooling, needle-like crystals were formed.

Here is a photomicrograph[3] of tyrosine crystals:


Here is a portrait [4] of Justus Freiherr von Liebig: