Tyrosine

About Tyrosine

L tyrosine is an amino acid made in the body from phenylalanine by the enzyme phenylalanine hydroxylase, so it becomes essential only in conditions such as phenylketonuria, in which this enzyme is deficient. The name derives from the Greek tyros, meaning cheese, because Justus von Liebig first isolated it from the milk protein casein in 1846. Tyrosine is the starting material for the catecholamine neurotransmitters dopamine, norepinephrine, and epinephrine, for the thyroid hormones, and for the pigment melanin. Its conversion to L DOPA by tyrosine hydroxylase is the tightly regulated, rate limiting step of catecholamine synthesis. Studies, many in military settings, have examined tyrosine for maintaining cognition under acute stressors such as cold, noise, and sleep deprivation, with some positive findings, but it does not appear to enhance unstressed performance and has not proven effective for depression. Food sources include cheese, meat, fish, eggs, soy, and beans. Interactions with MAOI antidepressants and thyroid medication are listed as concerns.