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[Biochemistry](https://durgical.com/en/biochemistry/) · Protein

# Apolipoprotein B (ApoB-100 and ApoB-48)

ApoB is the structural protein of chylomicrons, VLDL, IDL and LDL: each of these particles carries a single copy.

Updated 2026-11-01

## Key facts

- One gene gives two proteins: ApoB-100 in the liver and ApoB-48 in the gut, through mRNA editing (APOBEC-1 creates a stop codon).
- ApoB-48 (48% of the length) builds chylomicrons; ApoB-100 builds VLDL, IDL and LDL.
- Only ApoB-100 has the domain that binds the LDL receptor.
- To form a particle it needs MTP, which loads it with lipid in the ER.
- One atherogenic particle carries one ApoB: measuring ApoB counts the particles.

**Also called**
ApoB

**Genes**
APOB

## Structure

- ApoB-100 is huge (4,563 residues, about 515 kDa) and non-exchangeable: it stays on the particle for life.
- It wraps the particle like a belt; there is no complete crystal structure.

## Regulation

- It is made continuously; what is regulated is how much is degraded before secretion, depending on available lipid and insulin.

## Inhibitors and toxins

- Lomitapide inhibits MTP and slows secretion of ApoB particles
- Mipomersen, an antisense oligonucleotide against APOB mRNA (withdrawn in many countries)

## Clinical notes

- APOB variants that impair receptor binding (such as Arg3500Gln) cause familial hypercholesterolaemia (familial defective ApoB).
- Truncating variants cause familial hypobetalipoproteinaemia; loss of MTP causes abetalipoproteinaemia.
- ApoB and non-HDL cholesterol estimate risk better when triglycerides are high or in diabetes.

## Related conditions

- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)
- [Abetalipoproteinemia (Bassen–Kornzweig syndrome)](https://durgical.com/en/conditions/abetalipoproteinemia/)
- [Atherosclerosis and dyslipidaemia](https://durgical.com/en/conditions/atherosclerosis-and-dyslipidaemia/)

## Related

- [LDL (low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/ldl/)
- [VLDL (very-low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/vldl/)
- [Chylomicron](https://durgical.com/en/biochemistry/topics/chylomicron/)
- [LDL receptor](https://durgical.com/en/biochemistry/enzymes/ldl-receptor/)
- [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/)

## Test yourself

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

## How do two proteins, ApoB-100 and ApoB-48, come from one gene?

In the gut, APOBEC-1 edits the mRNA and creates a stop codon: the protein ends at 48% of its length.

## Why are chylomicron remnants not taken up via ApoB-48?

ApoB-48 lacks the LDL receptor-binding domain; remnants enter via ApoE.

## What does blood ApoB measure?

The number of atherogenic particles, since each VLDL, IDL, LDL or Lp(a) carries one ApoB.

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

Sources: [APOB: Apolipoprotein B-100 (human)](https://rest.uniprot.org/uniprotkb/P04114.txt) (UniProt, 2026); [APOB gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/apob/) (MedlinePlus, US National Library of Medicine, 2026); [MTTP gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/mttp/) (MedlinePlus, US National Library of Medicine, 2026); [Chylomicron assembly (R-HSA-8963888)](https://reactome.org/PathwayBrowser/#/R-HSA-8963888) (Reactome, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/apolipoprotein-b/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/apolipoprotein-b/