Tyrosine

The direct precursor of dopamine, noradrenaline, adrenaline and the thyroid hormones. Synthesised from phenylalanine.

What tyrosine does in the body

Tyrosine comes from food or is made in the liver from phenylalanine. In nerve cells and the adrenal medulla, tyrosine hydroxylase with BH4 and iron turns it into L-dopa – the step that sets the pace of the whole chain. With vitamin B6 dopamine is formed, with vitamin C and copper noradrenaline, and in the adrenal medulla this becomes adrenaline with a methyl group from SAM; cortisol stimulates this last step. In the thyroid, tyrosine residues of the protein thyroglobulin are loaded with iodine and linked to form T4 and T3. In the pigment cells, the copper-containing enzyme tyrosinase makes melanin from tyrosine. Tyrosine is broken down in the liver with vitamin B6 and vitamin C to fumarate and acetoacetate.

Low tyrosine – what happens in the body?

With a normal supply, tyrosine hydroxylase is largely saturated with tyrosine. But when nerve cells fire a lot and for long periods under heavy strain, more dopamine and noradrenaline is used up, and in studies tyrosine availability then limited replenishment. For the thyroid hormones, iodine supply is usually more decisive than tyrosine. Low values occur with low protein intake, with phenylketonuria, because the liver then cannot make tyrosine from phenylalanine, and when little BH4 is available.

High tyrosine – what happens in the body?

More tyrosine does not automatically lead to more messengers, because tyrosine hydroxylase is slowed by its own products. Raised values arise when breakdown in the liver is slowed: with impaired liver function, with vitamin C deficiency, because one breakdown enzyme needs vitamin C, temporarily in newborns whose liver enzymes have not yet matured, and in the rare inherited tyrosinaemias, in which tyrosine and, depending on the type, harmful breakdown products accumulate in the liver, kidneys, eyes or skin.

The interpretation is given in your report.