Biochemistry · Topic
Transamination and deamination !
This is how amino acids lose their nitrogen: transaminases collect it on glutamate and glutamate dehydrogenase releases it as ammonia.
Updated 2026-11-01
Key facts
- Transamination: the amino group of an amino acid moves to α-ketoglutarate, leaving glutamate and the matching keto acid.
- All transaminases use pyridoxal phosphate (B6) and are reversible.
- Oxidative deamination: glutamate dehydrogenase releases NH₄⁺ from glutamate and regenerates α-ketoglutarate.
- Lysine and threonine are not transaminated.
In detail
- Step 1: a transaminase (ALT, AST and others) moves the amino acid's amino group to α-ketoglutarate.
- PLP takes the amino group and becomes pyridoxamine phosphate; it then hands it to the acceptor keto acid (ping-pong mechanism).
- Step 2: in liver mitochondria, glutamate dehydrogenase releases NH₄⁺ from glutamate.
- NH₄⁺ enters the urea cycle through CPS-I; the other urea nitrogen arrives as aspartate, made by AST.
- Peripheral tissues send their nitrogen as glutamine and muscle sends it as alanine (glucose–alanine cycle).
- The leftover carbon skeletons go to gluconeogenesis, ketogenesis or the Krebs cycle.
Clinical notes
- Blood ALT and AST are markers of liver damage; the AST/ALT ratio hints at the cause.
- B6 deficiency (isoniazid, alcohol use disorder) slows the transaminases and other PLP enzymes.
Pathways
Related conditions
Related
- Alanine aminotransferase (ALT, GPT)
- Aspartate aminotransferase (AST, GOT)
- Glutamate dehydrogenase (GDH)
- Glutamate (glutamic acid)
- Glutamine
- Ammonia (ammonium)
- Glutamine synthetase
- Glucogenic and ketogenic amino acids
Test yourself
Think of the answer, then tap the question to see it.
Which coenzyme do all transaminases use?
Pyridoxal phosphate, made from vitamin B6, which carries the amino group from one substrate to another.
What is transdeamination?
A transamination that collects the amino group on glutamate, followed by GDH deamination of glutamate, which releases it as NH₄⁺.
Which two amino acids are not transaminated?
Lysine and threonine; they lose their nitrogen by other routes.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Glutamate and glutamine metabolism (Reactome, 2026); Metabolism of amino acids and derivatives (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.