AskDefine | Define sphingomyelin

User Contributed Dictionary

English

Noun

  1. a phospholipid, derived from sphingosine and choline, found in nerve tissue

Extensive Definition

Sphingomyelin(SPH) is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath which surrounds some nerve cell axons. It usually consists of phosphorylcholine and ceramide. In humans SPH represents ~85% of all sphingolipids.

Composition

In humans, it is the only membrane phospholipid not derived from glycerol.
Like all sphingolipids, SPH has a ceramide core (sphingosine bonded to a fatty acid via an amide linkage). In addition it contains one polar head group, which is either phosphocholine or phosphoethanolamine.

Function and location

The function of sphingomyelin remained unclear until recently when it was found to have a function in signal transduction.
Sphingomyelin is only found in the exoplasmic face of the cell membrane.

Abnormalities and associated diseases

Sphingomyelin can accumulate in a rare hereditary disease called Niemann-Pick Disease, types A and B. It is a genetically-inherited disease caused by a deficiency in the enzyme Sphingomyelinase, which causes the accumulation of Sphingomyelin in spleen, liver, lungs, bone marrow, and the brain, causing irreversible neurological damage. Of the two types involving Sphingomyelinase, type A occurs in infants. It is characterized by jaundice, an enlarged liver, and profound brain damage. Children with this type rarely live beyond 18 months. Type B involves an enlarged liver and spleen, which usually occurs in the pre-teen years. The brain is not affected. Most patients present with <1% normal levels of the enzyme in comparison to normal levels.
An excess of spingomyelin in the red blood cell membrane (as in abetalipoproteinemia) causes excess lipid accumulation in the outer leaflet of the red blood cell plasma membrane. This results in abnormally shaped red cells called acanthocytes.

Additional images

Image:Sphingomyelin-horizontal-3D-balls.png|Ball-and-stick model of sphingomyelin Image:Sphingomyelin-horizontal-2D-skeletal.png|Skeletal formula of sphingomyelin Image:Ceramid.svg |ceramide Image:Sphingosine-2D-skeletal.png |Sphingosine

External links

sphingomyelin in German: Sphingomyeline
sphingomyelin in Italian: Sfingomielina
sphingomyelin in Japanese: スフィンゴミエリン
sphingomyelin in Polish: Sfingomielina
sphingomyelin in Russian: Сфингомиелин
Privacy Policy, About Us, Terms and Conditions, Contact Us
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2
Material from Wikipedia, Wiktionary, Dict
Valid HTML 4.01 Strict, Valid CSS Level 2.1