Tyrosine

Tyrosine is a protein-building amino acid and a precursor to catecholamines, thyroid hormones, and melanin. Its aromatic side chain can be modified by enzymes and phosphorylated in proteins.

Phenylalanine hydroxylase: An enzyme that converts phenylalanine into tyrosine by adding a hydroxyl group. This enzyme supplies tyrosine from phenylalanine, linking its production to an essential dietary amino acid.
Amino acid: An organic molecule with amino and carboxyl groups that serves as a protein building block or metabolic intermediate. Tyrosine is one of the amino acids incorporated into proteins.
Phenylketonuria: An inherited disorder in which impaired phenylalanine metabolism can cause toxic phenylalanine accumulation. Low conversion of phenylalanine to tyrosine makes dietary tyrosine important in its management.
Serine: A protein-building amino acid with a hydroxyl-bearing side chain. Serine can also be phosphorylated, but lacks tyrosine's aromatic ring.
Catecholamine biosynthesis: The sequence of reactions that produces dopamine, norepinephrine, and epinephrine. Tyrosine is the starting substrate for this hormone and neurotransmitter pathway.
Aromatic amino acid: An amino acid whose side chain contains an aromatic ring. Tyrosine's aromatic ring gives it distinctive chemical and spectroscopic properties.
Alkaptonuria: An inherited metabolic disorder caused by deficiency of homogentisate 1,2-dioxygenase. The disease disrupts a tyrosine degradation pathway and causes homogentisic acid accumulation.
Tryptophan: An essential aromatic amino acid with an indole side chain. Like tyrosine, it is aromatic, but its metabolic products and dietary status differ.
Tyrosine hydroxylase: An enzyme that converts tyrosine into L-DOPA, the rate-limiting step in catecholamine synthesis. It initiates catecholamine production by hydroxylating tyrosine.
Phenylalanine: An essential aromatic amino acid that can be converted into tyrosine. Phenylalanine is tyrosine's metabolic precursor and a close structural relative.

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