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# Mitochondrial NADH shuttles

Glycolytic NADH cannot cross the inner membrane; two shuttles carry its electrons into the mitochondrion, with different ATP yields.

Updated 2026-11-01

## Key facts

- Malate–aspartate: liver, kidney and heart; electrons arrive as matrix NADH and yield about 2.5 ATP.
- Glycerol-3-phosphate: skeletal muscle and brain; electrons arrive as FADH₂ at ubiquinone and yield about 1.5 ATP.
- That is why the total per glucose is given as 30 or 32 ATP depending on the shuttle.
- The malate–aspartate shuttle is reversible and needs transaminases (AST) with vitamin B6.

## In detail

- Malate–aspartate, step 1: in the cytosol, malate dehydrogenase reduces oxaloacetate to malate using NADH.
- Step 2: malate enters the matrix on a carrier in exchange for α-ketoglutarate.
- Step 3: in the matrix, malate dehydrogenase oxidises it and regenerates NADH, which goes to complex I.
- Step 4: oxaloacetate is transaminated to aspartate, which leaves for the cytosol and becomes oxaloacetate again.
- Glycerol-3-phosphate: the cytosolic enzyme reduces dihydroxyacetone phosphate to glycerol-3-phosphate using NADH.
- Mitochondrial glycerol-3-phosphate dehydrogenase (GPD2, with FAD) on the outer face of the inner membrane passes the electrons to ubiquinone.

**Also called**
Malate–aspartate shuttle, Glycerol-3-phosphate shuttle

## Clinical notes

- When the shuttles cannot keep up (intense exercise), cytosolic NADH is reoxidised by making lactate.
- The AST of the malate–aspartate shuttle is the same transaminase measured in liver tests.

## Pathways

- [Electron transport chain and oxidative phosphorylation](https://durgical.com/en/biochemistry/pathways/electron-transport-chain-and-oxidative-phosphorylation/)
- [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/)
- [Malate–aspartate shuttle](https://durgical.com/en/biochemistry/pathways/malate-aspartate-shuttle/)

## Related

- [NAD⁺ (nicotinamide adenine dinucleotide)](https://durgical.com/en/biochemistry/molecules/nad/)
- [FAD (flavin adenine dinucleotide)](https://durgical.com/en/biochemistry/molecules/fad/)
- [Ubiquinone (coenzyme Q₁₀)](https://durgical.com/en/biochemistry/molecules/ubiquinone/)
- [Complex I (NADH dehydrogenase)](https://durgical.com/en/biochemistry/enzymes/complex-i/)
- [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/)

## Test yourself

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

## Why do NADH shuttles exist?

The inner mitochondrial membrane is impermeable to NADH; the shuttles move only its electrons.

## Which shuttle yields less ATP, and why?

The glycerol-3-phosphate shuttle: it delivers the electrons as FADH₂ to ubiquinone and skips complex I (about 1.5 ATP).

## In which tissues does the malate–aspartate shuttle predominate?

In the liver, kidney and heart.

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

Sources: [Malate-aspartate shuttle](https://reactome.org/PathwayBrowser/#/R-HSA-9856872) (Reactome, 2026); [GPD2: Glycerol-3-phosphate dehydrogenase, mitochondrial (human)](https://www.uniprot.org/uniprotkb/P43304/entry) (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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