tyrosin

Tyrosin, also known as tyrosine in many contexts, is one of the standard amino acids used by organisms to build proteins. In humans, L-tyrosine is the biologically active form and is considered conditionally essential, meaning most people can synthesize enough under normal conditions but may require dietary intake in certain circumstances (for example, during illness or in the metabolic disorder phenylketonuria).

Biosynthesis and metabolism

Tyrosine is produced in the body from phenylalanine through the action of the enzyme phenylalanine hydroxylase, with the cofactor tetrahydrobiopterin. It can also be obtained directly from the diet. In the body, tyrosine serves as a precursor for several important compounds: the catecholamines dopamine, norepinephrine, and epinephrine; the thyroid hormones thyroxine (T4) and triiodothyronine (T3); and the pigment melanin. Tyrosine is further degraded through a series of steps that ultimately feed into energy production or other metabolic pathways. Defects in tyrosine metabolism can cause tyrosinemia, a rare inherited disorder.

Biological roles

As a precursor to key signaling molecules, tyrosine supports brain function and hormonal regulation. It participates in protein synthesis and in the production of melanin, influencing pigmentation. Its availability can influence cognitive function and stress responses in some contexts, particularly under acute stress, though clinical evidence varies.

Diet and supplementation

Tyrosine is present in protein-rich foods such as meats, fish, eggs, dairy products, soy, and legumes. It is also available as a dietary supplement, sometimes used with the aim of supporting cognitive performance or mood, but evidence for performance benefits is mixed and effects are highly context-dependent.

Medical relevance

In phenylketonuria, phenylalanine cannot be efficiently converted to tyrosine, making tyrosine essential in the diet for affected individuals. Conversely, disorders of tyrosine degradation can lead to metabolic disturbances and require medical management.