Tyrosine Hydroxylase (TH)

Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine (DOPA). DOPA is a precursor for dopamine which in turn is a precursor for norepinephrine (noradrenaline) and epinephrine (adrenaline).

In humans, tyrosine hydroxylase is encoded by the TH gene.The enzyme, an oxygenase, is found in the cytosol of all cells containing catecholamines. This initial reaction is the rate limiting step in the production of catecholamines.The enzyme is highly specific, not accepting indole derivatives - which is unusual as many other enzymes involved in the production of catecholamines do.