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[Biochemistry](https://durgical.com/en/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

- [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/)

## Related conditions

- [Hyperammonaemia](https://durgical.com/en/conditions/hyperammonaemia/)
- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)

## Related

- [Alanine aminotransferase (ALT, GPT)](https://durgical.com/en/biochemistry/enzymes/alanine-aminotransferase/)
- [Aspartate aminotransferase (AST, GOT)](https://durgical.com/en/biochemistry/enzymes/aspartate-aminotransferase/)
- [Glutamate dehydrogenase (GDH)](https://durgical.com/en/biochemistry/enzymes/glutamate-dehydrogenase/)
- [Glutamate (glutamic acid)](https://durgical.com/en/biochemistry/molecules/glutamate/)
- [Glutamine](https://durgical.com/en/biochemistry/molecules/glutamine/)
- [Ammonia (ammonium)](https://durgical.com/en/biochemistry/molecules/ammonia/)
- [Glutamine synthetase](https://durgical.com/en/biochemistry/enzymes/glutamine-synthetase/)
- [Glucogenic and ketogenic amino acids](https://durgical.com/en/biochemistry/topics/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.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Glutamate and glutamine metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-8964539) (Reactome, 2026); [Metabolism of amino acids and derivatives](https://reactome.org/PathwayBrowser/#/R-HSA-71291) (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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