Tyrosine

Tyrosine is an aromatic amino acid, one of the twenty amino acids needed for protein synthesis. It is formed from phenylalanine and other amino acids. Tyrosine is involved in the synthesis of adrenaline, noradrenaline, serotonin, and dopamine. For tyrosine to be properly utilized in the brain, its metabolism requires vitamin B₆ (pyridoxine) and folic acid. Tyrosine is used for the synthesis of proteins, catecholamines, thyroid hormones, melanins, and can break down into final metabolic products CO₂, H₂O, NH⁺, and energy. A transamination reaction occurs between tyrosine and α-ketoglutarate, forming p-hydroxyphenylpyruvate which reacts with O₂ to form homogentisate. Molecular oxygen then cleaves the aromatic homogentisate ring, forming maleylacetoacetate. It is isomerized to fumarylacetoacetate, which hydrolyzes into fumarate and acetoacetate. Tyrosine is characterized by mood-enhancing, antidepressant properties. It acts as an adaptogen – improving the body’s adaptation to stress reactions, reducing the negative effects of stress, and suppressing appetite. Tyrosine is involved in the synthesis of enkephalins – pain-relieving substances. It is used as a precursor for the neurotransmitter L-dopa in Parkinson’s disease. As an antidepressant substance, tyrosine is used in combination with tryptophan and imipramine. This amino acid is found in soy products, chicken, turkey, fish, bananas, milk, cheese, sesame seeds, and oat flakes. A deficiency in tyrosine leads to decreased protein synthesis, increased fatigue, signs of depression, impaired liver function, and decreased thyroid activity. A severe tyrosine deficiency may occur in genetic disorder – phenylketonuria, where the body cannot metabolize the amino acid phenylalanine and it needs to be eliminated from the diet. Without phenylalanine, tyrosine cannot be formed.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė