Sphingolipids are abundant components of the myelin sheath, a multilayered structure that protects and insulates cells of the central nervous system. Sphingolipids are also found in plant cells and yeast. Sphingolipids are derivatives of the base sphingosine (phytosphingosine in plants). They include ceramides, sphingomyelin, and glycosphingolipids. Glycosphingolipids include cerebrosides and gangliosides.

Ceramides are the precursors of sphingomyelin and the glycosphingolipids.

Ceramides are made as shown in Figure 19.13. Initially, palmitoyl-CoA is joined to serine, with loss of CoASH and CO2. Following reduction of the ketone group of the 3-ketosphinganine intermediate and acylation of the amine (from serine), a ceramide is produced.

Cerebrosides arise from ceramides by glycosylation (via UDP-glucose), as shown in Figure 19.13 and Figure 19.14. Globosides arise also from ceramides via a series of additions of glucose, galactose, and N-acetyl galactose to a ceramide (Figure 19.14).

Sphingomyelin arises from ceramide by transfer of a phosphocholine moiety from phosphatidylcholine to the ceramide (Figure 19.13).

1. Sphingolipid Metabolism

2. Sphingoglycolipid Metabolism