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.
The German chemist Justus Freiherr von Liebig discovered 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 of tyrosine crystals: