Figure 1.

Scheme of sphingolipid metabolism. Ceramide is formed either de novo starting from serine and palmitoylCoA or by hydrolysis of sphingomyelin or glycosphingolipids including gangliosides. In addition, its degradation product sphingosine can be recycled back to ceramide by ceramide synthase (CS). It is degraded by ceramidases (CDases) to yield sphingosine, which in turn is phosphorylated by sphingosine-kinases (SK) to generate sphingosine-1-phosphate (S1P). The latter is either cleaved by S1P-lyase (SPL) into hexadecenal and phosphoethanolamine or dephosphorylated back to sphingosine by S1P-phosphatases (SPP). SMS, sphingomyelin synthase; SMase, sphingomyelinase; SPT, serine palmitoyltransferase.