# Catecholamine Synthesis & Breakdown

**Catecholamine Synthesis** is a biochemical pathway used to produce dopamine, norepinephrine, and epinephrine. This process takes place in the **adrenal medulla** as well as the post-ganglionic fibers of the **sympathetic nervous system**.

The pathway begins with **phenylalanine**, which is converted into **tyrosine**. This reaction is catalyzed by the enzyme **phenylalanine hydroxylase**, and requires the cofactor, **BH4** (tetrahydrobiopterin). Notably, this reaction is impaired in patients with Phenylketonuria.

Next, tyrosine is converted into **DOPA**, by the enzyme **tyrosine hydroxylase**. Tyrosine hydroxylase also requires a **BH4** cofactor. Afterwards, DOPA is converted into **dopamine**, by the enzyme **DOPA decarboxylase**. This reaction requires [Vitamin B6 (Pyridoxine)](/content/view/3763/index.html) as a cofactor, and can be blocked by the drug, **carbidopa**.

Subsequently, dopamine is converted into **norepinephrine**. This reaction is catalyzed by **dopamine beta-hydroxylase**, and requires [Vitamin C (Ascorbic Acid)](/content/view/3717/index.html) as a cofactor. Finally, norepinephrine is methylated by **PNMT**, producing **epinephrine**. This reaction requires **SAM** as a cofactor, and can be stimulated by **cortisol**.

**Catecholamine Breakdown** is a separate biochemical pathway used to metabolize and eliminate catecholamines. Dopamine is degraded into **homovanillic acid**, while norepinephrine and epinephrine are first converted into **metanephrines** by the enzyme **COMT**. These metanephrines are then further degraded into **vanillylmandelic acid**, a reaction catalyzed by the MAO enzymes.