L-TYROSINE

Definition

Dietary supplement, nutrient. Flavouring ingredient

Description

Tyrosine is an essential amino acid that readily passes the blood-brain barrier. Once in the brain, it is a precursor for the neurotransmitters dopamine, norepinephrine and epinephrine, better known as adrenalin. These neurotransmitters are an important part of the body's sympathetic nervous system, and their concentrations in the body and brain are directly dependent upon dietary tyrosine. Tyrosine is not found in large concentrations throughout the body, probably because it is rapidly metabolized. Folic acid, copper and vitamin C are cofactor nutrients of these reactions. Tyrosine is also the precursor for hormones, thyroid, catecholestrogens and the major human pigment, melanin. Tyrosine is an important amino acid in many proteins, peptides and even enkephalins, the body's natural pain reliever. Valine and other branched amino acids, and possibly tryptophan and phenylalanine may reduce tyrosine absorption. A number of genetic errors of tyrosine metabolism occur. Most common is the increased amount of tyrosine in the blood of premature infants, which is marked by decreased motor activity, lethargy and poor feeding. Infection and intellectual deficits may occur. Vitamin C supplements reverse the disease. Some adults also develop elevated tyrosine in their blood. This indicates a need for more vitamin C. More tyrosine is needed under stress, and tyrosine supplements prevent the stress-induced depletion of norepinephrine and can cure biochemical depression. However, tyrosine may not be good for psychosis. Many antipsychotic medications apparently function by inhibiting tyrosine metabolism. L-dopa, which is directly used in Parkinson's, is made from tyrosine. Tyrosine, the nutrient, can be used as an adjunct in the treatment of Parkinson's. Peripheral metabolism of tyrosine necessitates large doses of tyrosine, however, compared to L-dopa.

L-Tyrosine is Found in These Foods

L-Tyrosine Health Effects

General Information

Metabolism: In the liver, L-tyrosine is involved in a number of biochemical reactions, including protein synthesis and oxidative catabolic reactions. L-tyrosine that is not metabolized in the liver is distributed via the systemic circulation to the various tissues of the body.
Uses/Sources: Tyrosine is claimed to act as an effective antidepressant, however results are mixed. Tyrosine has also been claimed to reduce stress and combat narcolepsy and chronic fatigue, however these claims have been refuted by some studies.
Route of Exposure: L-tyrosine is absorbed from the small intestine by a sodium-dependent active transport process.

Toxicity

Carcinogenicity: No indication of carcinogenicity to humans (not listed by IARC).
Toxicity: LD<sub>50</sub> (oral, rat) > 5110 mg/kg

Mechanism of Action

Tyrosine is produced in cells by hydroxylating the essential amino acid phenylalanine. This relationship is much like that between cysteine and methionine. Half of the phenylalanine required goes into the production of tyrosine; if the diet is rich in tyrosine itself, the requirements for phenylalanine are reduced by about 50%. The mechanism of L-tyrosine's antidepressant activity can be accounted for by the precursor role of L-tyrosine in the synthesis of the neurotransmitters norepinephrine and dopamine. Elevated brain norepinephrine and dopamine levels are thought to be associated with antidepressant effects.

Target Name	Mechanism of Action	References
Tyrosine 3-monooxygenase Tyrosine aminotransferase Tyrosine--tRNA ligase, mitochondrial Tyrosine--tRNA ligase, cytoplasmic Tubulin--tyrosine ligase		17451064 17139284 17604359 20545322 17578016 15840835 17016423 12754495 11752352 17401211 17561836 17520326 17389761 12097643