Dopamine, noradrenaline, adrenaline: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Dopamine, noradrenaline, adrenaline: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Dopamine, noradrenaline and adrenaline are catecholamines formed from the amino acids phenylalanine and tyrosine. They carry signals in the nervous system; adrenaline also acts as a hormone from the adrenal medulla.

The pathway step by step

1. Phenylalanine → Tyrosine PAH · BH4, Iron Phenylalanine hydroxylase (PAH) attaches an OH group to phenylalanine, forming tyrosine. The enzyme needs iron and the cofactor tetrahydrobiopterin (BH4). Source 2, 3, 1
2. Tyrosine → L-DOPA Tyrosine hydroxylase · BH4, Iron Tyrosine hydroxylase turns tyrosine into L-DOPA; it too needs iron and BH4. This is the slowest step of the pathway – here the cell regulates how much is formed. Source 1, 3
3. L-DOPA → Dopamine AADC · Vitamin B6 (PLP) The enzyme AADC (decarboxylase) removes a carboxyl group from L-DOPA, forming dopamine. It needs pyridoxal phosphate, the active form of vitamin B6. Source 4, 1
4. Dopamine → Noradrenaline Dopamine β-hydroxylase · Vitamin C, Copper In storage vesicles, dopamine β-hydroxylase attaches an OH group to dopamine. This copper-containing enzyme uses vitamin C (ascorbate) as an electron donor. Source 1, 5
5. Noradrenaline → Adrenaline PNMT · SAM In the adrenal medulla, PNMT transfers a methyl group from SAM (S-adenosylmethionine) to noradrenaline. The formation of this enzyme is regulated mainly by cortisol. Source 6, 1
6. DOPAC → Homovanillic acid COMT · SAM The enzyme COMT (catechol-O-methyltransferase) attaches a methyl group to DOPAC. This forms homovanillic acid, which is excreted in urine. Source 7
7. DHPG → MHPG COMT · SAM Outside the nerve cells, COMT attaches a methyl group to DHPG. This forms MHPG. Source 7
8. MHPG → Vanillylmandelic acid ADH, ALDH · NAD⁺ In the liver, alcohol and aldehyde dehydrogenases convert MHPG into vanillylmandelic acid. The metanephrines also lead into this substance via MAO. Source 7
9. Metanephrines → Vanillylmandelic acid MAO In the liver, alcohol and aldehyde dehydrogenases convert MHPG into vanillylmandelic acid. The metanephrines also lead into this substance via MAO. Source 7

Cofactors in this pathway

• Tetrahydrobiopterin (BH4) — Cofactor of phenylalanine and tyrosine hydroxylase when oxygen is inserted Source 3
• Iron — Sits in the active site of phenylalanine and tyrosine hydroxylase Source 1, 2In the ORY catalogue as a laboratory value: Eisen
• Vitamin B6 — As pyridoxal phosphate, cofactor of AADC, which converts L-DOPA into dopamine Source 4In the ORY catalogue as a laboratory value: Vitamin B6
• Copper — Metal at the centre of dopamine β-hydroxylase, which converts dopamine into noradrenaline Source 5In the ORY catalogue as a laboratory value: Kupfer (Cu)
• Vitamin C — Electron donor of dopamine β-hydroxylase inside the storage vesicle Source 5In the ORY catalogue as a laboratory value: Vitamin C (Ascorbinsäure)
• SAM (from methionine) — Methyl group donor of PNMT and of COMT Source 6, 7In the ORY catalogue as a laboratory value: Methionin
• Magnesium — Ion in the active site of COMT when catecholamines are converted Source 9In the ORY catalogue as a laboratory value: Magnesium
• NAD⁺ — Accepts hydrogen at the aldehyde dehydrogenases of the breakdown route Source 7In the ORY catalogue as a laboratory value: NAD⁺ (Nicotinamidadenindinukleotid)

What acts on this pathway

• Carbidopa — Carbidopa inhibits the decarboxylase outside the brain, so less L-DOPA is converted to dopamine there. Carbidopa does not enter the brain. The product information describes this mechanism. Source 8

Sources

1. Daubner SC, Le T, Wang S. Tyrosine hydroxylase and regulation of dopamine synthesis. Arch Biochem Biophys 2011 · PubMed 21176768
2. Flydal MI, Martinez A. Phenylalanine hydroxylase: function, structure, and regulation. IUBMB Life 2013 · PubMed 23457044
3. Werner ER, Blau N, Thöny B. Tetrahydrobiopterin: biochemistry and pathophysiology. Biochem J 2011 · PubMed 21867484
4. Paiardini A, Giardina G, Rossignoli G et al. New Insights Emerging from Recent Investigations on Human Group II Pyridoxal 5'-Phosphate Decarboxylases. Curr Med Chem 2017 · PubMed 27881066
5. Prigge ST, Mains RE, Eipper BA et al. New insights into copper monooxygenases and peptide amidation: structure, mechanism and function. Cell Mol Life Sci 2000 · PubMed 11028916
6. Wong DL. Epinephrine biosynthesis: hormonal and neural control during stress. Cell Mol Neurobiol 2006 · PubMed 16645894
7. Eisenhofer G, Kopin IJ, Goldstein DS. Catecholamine metabolism: a contemporary view with implications for physiology and medicine. Pharmacol Rev 2004 · PubMed 15317907
8. US prescribing information Sinemet (Carbidopa/Levodopa, DailyMed), section Clinical Pharmacology, Pharmacodynamics · Prescribing information
9. Ma Z, Liu H, Wu B. Structure-based drug design of catechol-O-methyltransferase inhibitors for CNS disorders. Br J Clin Pharmacol 2014 · PubMed 23713800

Related pathways

• Vitamin B6 — l-dopa
• Carnitine — Eisen, Vitamin B6
• Estradiol — Eisen, Methionin
• Estrogen breakdown — Eisen, Methionin
• Spermidine — Eisen, Vitamin B6

As of 2026-09-16. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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