Biochemistry · Molecule
Sphingomyelin !
Sphingomyelin is the sphingolipid with phosphate: rich in myelin and the outer leaflet of membranes. It builds up in Niemann–Pick disease.
Updated 2026-11-01
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Key facts
- Ceramide + phosphocholine; it is both a sphingolipid and a phospholipid.
- It is made in the Golgi: sphingomyelin synthase moves phosphocholine from phosphatidylcholine to ceramide.
- Lysosomal acid sphingomyelinase breaks it into ceramide + phosphocholine; its deficiency causes Niemann–Pick A and B.
- With cholesterol it forms the lipid rafts of the outer leaflet.
- Also called
- N-stearoyl sphingomyelin (3D model)
- Formula
- C₄₁H₈₃N₂O₆P
- PubChem
- CID 6453725
Structure
- The 3D model (PDB A1H8M) is C18 sphingomyelin: sphingosine + stearate + phosphocholine.
- The same phosphocholine head as lecithin, but on a sphingosine backbone instead of glycerol.
Clinical notes
- In Niemann–Pick A/B it accumulates in macrophages (foam cells) of liver, spleen, lung and bone marrow.
- An amniotic fluid lecithin/sphingomyelin ratio above 2 indicates mature fetal lungs.
Related conditions
Related
- Ceramide
- Acid sphingomyelinase
- Phosphatidylcholine (lecithin)
- Sphingolipids and sphingolipidoses
- Membrane structure
- Phospholipids
Test yourself
Think of the answer, then tap the question to see it.
How does sphingomyelin differ chemically from phosphatidylcholine?
Both carry phosphocholine, but sphingomyelin is built on ceramide (sphingosine) and lecithin on glycerol.
Which enzyme breaks down sphingomyelin in the lysosome?
Acid sphingomyelinase (SMPD1 gene), which splits it into ceramide and phosphocholine.
What does an amniotic lecithin/sphingomyelin ratio above 2 indicate?
Enough surfactant: the fetal lungs are mature.
Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: N-Stearoylsphingomyelin (CID 6453725) (PubChem, NCBI, 2026) · Public domain; RCSB PDB - A1H8M Ligand Summary Page (RCSB Protein Data Bank, 2026); Sphingolipid metabolism (Reactome, 2026); SMPD1 gene: MedlinePlus Genetics (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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Representative model, for educational purposes only.