Tyrosine: Definition and Function

What is Tyrosine?

Tyrosine is a non-essential amino acid, which is part of proteins and is considered an aromatic amino acid. It is synthesized from the hydroxylation of phenylalanine, provided it contains a sufficient supply of this amino acid.

The name tyrosine (tyros) means cheese in Greek and this amino acid gets its name because it was first discovered in the cheese protein, casein.

The side chain of tyrosine is a phenolic group. Three different isomers of the amino acid tyrosine are known: para-tyrosine, meta-tyrosine and ortho-tyrosine. However, the best known and most studied form is para-tyrosine, also known as L-tyrosine.

Tyrosine is a precursor to thyroid hormones (thyroxine), catecholamines (dopamine, adrenaline and norepinephrine) and melanin, which is the pigment responsible for coloring hair and skin.

The function of catecholamines is mediated by their binding to different receptors (alpha-adrenergic, beta-adrenergic or dopamine receptors). Depending on the receptor they bind to, they will have different physiological effects. Catecholamines and thyroid hormones play an important role in metabolism and the regulation of body weight.

Tyrosine can also be broken down for energy, generating fumarate and acetoacetate in its metabolism.

Fumarate can be used to produce energy in the Krebs cycle or used to form glucose through gluconeogenesis. Acetoacetate can be used for lipid synthesis or for energy production in the form of acetyl CoA.

Tyrosine occurs naturally in animal foods like meat, fish, dairy, and eggs, as well as plant foods like legumes, seeds, whole grains, almonds, chard, apples, asparagus, avocados, carrots, lettuce, spinach, soy products, watermelon, cucumber, parsley and watercress.