Tyrosine hydroxylase

Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to dihydroxyphenylalanine (DOPA). It does so using tetrahydrobiopterin as a coenzyme. 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.

Reaction

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.

<br style="clear:left;"/>

Clinical significance

Tyrosine hydroxylase can be inhibited by the drug α-methyl-para-tyrosine (Metirosine). This inhibition can lead to a depletion of dopamine and norepinepherine in the brain due to the lack of the precursor L-Dopa (L-3,4-dyhydroxyphenylalanine) which is synthesized by tyrosine hydroxylase. This drug is rarely used and can cause depression, but it is useful in treating pheochromocytoma and also resistant hypertension.

<br style="clear:left;"/>

Tyrosine hydroxylase is an autoantigen in Autoimmune Polyendocrine Syndrome ......
Read More