Tyrosine hydroxylase

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Tyrosine hydroxylase is the enzyme responsible for catalyzing the conversion of L-tyrosine, an amino acid, to dihydroxyphenylalanine (DOPA), a precursor to dopamine.

The enzyme 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.

Tyrosine hydroxylase can be inhibited by the drug α-methyl tyrosine (Metirosine), however it is not an effective means of regulating noreadrenaline synthesis. This drug is rarely used, but it is useful in treating phaeochromocytoma (pheochromocytoma)and also resistant hypertension.