sfingomyeliini

Sfingomyeliini, known in English as sphingomyelin, is a family of sphingophospholipids composed of a ceramide backbone linked to a phosphocholine head group. They constitute a major component of animal cell membranes and are particularly abundant in the myelin sheaths surrounding axons in the central and peripheral nervous systems.

Chemically, the ceramide consists of a fatty acid amide-linked to a sphingosine base; the phosphocholine head group gives the molecule its zwitterionic character. Sphingomyelin is synthesized in the Golgi apparatus by sphingomyelin synthase, which transfers the phosphocholine group from phosphatidylcholine to ceramide, producing sphingomyelin and diacylglycerol. Degradation is performed by sphingomyelinases, which hydrolyze sphingomyelin to ceramide and phosphorylcholine.

In membranes, sphingomyelin contributes to lipid raft formation and membrane stability. Ceramide generated by hydrolysis acts as a second messenger in signaling pathways regulating cell growth, differentiation, and apoptosis; sphingomyelin turnover influences several cellular processes and stress responses.

Clinical significance: Altered sphingomyelin metabolism is implicated in lysosomal storage disorders, notably Niemann-Pick disease types A and B, caused by a deficiency of acid sphingomyelinase and resulting in accumulation of sphingomyelin in organs. Sphingomyelin levels are used in certain diagnostic contexts and research on neurodegenerative diseases.