L-tyrosine is a protein amino acid. It is classified as a conditionally essential amino acid. Under most circumstances, the body can synthesize sufficient L-tyrosine, principally from L-phenylalanine, to meet its physiological demands. However, there are conditions where the body requires a dietary source of the amino acid for its physiological demands. For example, L-tyrosine is an essential amino acid for those with phenylketonuria. L-tyrosine is found mostly in protein. Dietary sources of L-tyrosine are derived from animal and vegetable proteins. Vegetables and juices contain small amounts of L-tyrosine. L-tyrosine is also found in fermented foods, such as yogurt and miso.
In addition to being involved in protein synthesis, L-tyrosine is a precursor for the synthesis of epinephrine, norepinephrine, dopamine, thyroxine, triiodothyronine, and the pigment melanin.