Biochemistry · Topic
Molecules derived from amino acids !
Besides building proteins, amino acids give hormones, neurotransmitters, pigments and key molecules such as nitric oxide, creatine and haem.
Updated 2026-11-01
Key facts
- Tyrosine → catecholamines (dopamine, noradrenaline, adrenaline), melanin and thyroid hormones.
- Tryptophan → serotonin, melatonin and niacin; histidine → histamine; glutamate → GABA.
- Arginine → nitric oxide, creatine (with glycine and SAM), urea and polyamines (via ornithine).
- Glycine → haem (with succinyl-CoA), creatine, glutathione and bile acid conjugation.
- The decarboxylases that make dopamine, serotonin, histamine and GABA use pyridoxal phosphate (B6).
In detail
- Catecholamines: tyrosine → L-DOPA (tyrosine hydroxylase, BH4) → dopamine (DOPA decarboxylase, B6) → noradrenaline (dopamine β-hydroxylase, vitamin C and copper) → adrenaline (PNMT, SAM; induced by cortisol).
- Serotonin and melatonin: tryptophan → 5-hydroxytryptophan (tryptophan hydroxylase, BH4) → serotonin (B6) → N-acetylserotonin → melatonin in the pineal gland.
- Niacin: tryptophan passes through kynurenine and forms NAD⁺; the route needs B6 and B2.
- Histamine: histidine decarboxylase (B6) makes it in mast cells, basophils and stomach cells.
- GABA: glutamate decarboxylase (B6) makes it in inhibitory neurons.
- Nitric oxide: nitric oxide synthase (BH4, NADPH) turns arginine into citrulline and NO, which relaxes smooth muscle via cGMP.
- Creatine: arginine + glycine → guanidinoacetate (kidney); SAM methylates it in the liver; muscle phosphorylates it, and its product creatinine is excreted at a nearly constant rate.
Clinical notes
- Phaeochromocytoma: excess catecholamines; metanephrines are measured.
- Carcinoid tumour: excess serotonin; urinary 5-HIAA is measured.
- Blood creatinine is used to estimate glomerular filtration.
- B6 deficiency can cause seizures (less GABA) and anaemia (less haem).
Pathways
Related conditions
Related
- Tyrosine
- Tryptophan
- Glutamate (glutamic acid)
- Tyrosine hydroxylase
- Tetrahydrobiopterin (BH4)
- S-adenosylmethionine (SAM)
- NAD⁺ (nicotinamide adenine dinucleotide)
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme turns noradrenaline into adrenaline, and which donor does it use?
Phenylethanolamine N-methyltransferase (PNMT), with SAM as methyl donor; cortisol induces it in the adrenal medulla.
Which amino acid gives rise to nitric oxide?
Arginine; nitric oxide synthase turns it into citrulline and NO.
Which vitamin do the dopamine, serotonin, histamine and GABA decarboxylases share?
B6, as pyridoxal phosphate.
Which urinary metabolite is measured to look for a carcinoid tumour?
5-Hydroxyindoleacetic acid (5-HIAA), the breakdown product of serotonin.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Catecholamine biosynthesis (Reactome, 2026); Serotonin and melatonin biosynthesis (Reactome, 2026); Creatine metabolism (Reactome, 2026); Histidine catabolism (Reactome, 2026); GABA synthesis, release, reuptake and degradation (Reactome, 2026).
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Representative model, for educational purposes only.