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# Odd-chain fatty acids and propionate metabolism

Odd-numbered fatty acids end as propionyl-CoA, which biotin and vitamin B12 turn into succinyl-CoA.

Updated 2026-11-01

## Key facts

- The last β-oxidation turn of an odd-chain fatty acid leaves 1 propionyl-CoA (3 C) and 1 acetyl-CoA.
- Propionyl-CoA carboxylase (biotin, ATP) → D-methylmalonyl-CoA → racemase → L-methylmalonyl-CoA.
- Methylmalonyl-CoA mutase (adenosylcobalamin, B12) → succinyl-CoA, which enters the Krebs cycle.
- It is the only route by which part of a fatty acid gives net glucose.

## In detail

- Sources of propionyl-CoA: odd-chain fatty acids (dairy, ruminant fat), valine, isoleucine, methionine, threonine, the cholesterol side chain and gut fermentation.
- Propionyl-CoA carboxylase adds CO₂ with biotin and forms D-methylmalonyl-CoA.
- Methylmalonyl-CoA epimerase converts it to the L isomer.
- Methylmalonyl-CoA mutase rearranges the skeleton to form succinyl-CoA; it needs vitamin B12 as adenosylcobalamin.
- Succinyl-CoA follows the Krebs cycle to oxaloacetate, which can go to gluconeogenesis.

**Also called**
Propionyl-CoA pathway, Methylmalonyl-CoA pathway

## Clinical notes

- Propionic acidaemia (carboxylase missing): vomiting, acidosis, hyperammonaemia and ketosis in the newborn.
- Methylmalonic acidaemia (mutase or adenosylcobalamin synthesis missing): a similar picture with very high methylmalonic acid.
- Vitamin B12 deficiency: methylmalonic acid rises and helps tell it from folate deficiency (homocysteine rises in both).

## Pathways

- [Fatty acid β-oxidation](https://durgical.com/en/biochemistry/pathways/fatty-acid-oxidation/)
- [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/)
- [Propionyl-CoA to succinyl-CoA](https://durgical.com/en/biochemistry/pathways/propionyl-coa-to-succinyl-coa/)

## Related

- [Propionyl-CoA](https://durgical.com/en/biochemistry/molecules/propionyl-coa/)
- [Acetyl-CoA](https://durgical.com/en/biochemistry/molecules/acetyl-coa/)
- [Krebs cycle (citric acid cycle)](https://durgical.com/en/biochemistry/pathways/krebs-cycle/)
- [Fatty acid β-oxidation](https://durgical.com/en/biochemistry/pathways/fatty-acid-oxidation/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzyme of the propionate pathway needs vitamin B12?

Methylmalonyl-CoA mutase, which uses adenosylcobalamin.

## Which marker tells B12 deficiency from folate deficiency?

Methylmalonic acid, which rises in B12 deficiency but not in folate deficiency.

## Which Krebs cycle intermediate does propionyl-CoA end up as?

Succinyl-CoA.

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

Sources: [Propionyl-CoA catabolism](https://reactome.org/PathwayBrowser/#/R-HSA-71032) (Reactome, 2026); [Propionic acidemia: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/propionic-acidemia/) (MedlinePlus, US National Library of Medicine, 2026); [Methylmalonic acidemia: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/methylmalonic-acidemia/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/odd-chain-fatty-acids-and-propionate-metabolism/