Figure 1.

Schematic diagram illustrating sphingolipid synthesis and metabolism. 1) Serine palmitoyltransferase catalyzes the condensation of serine and palmitoyl CoA. 2) 3-Ketosphinganine reductase catalyzes sphinganine formation. 3) Dihydroceramide synthases add a second acyl chain to sphinganine resulting in dihydroceramide formation. 4) Dihydroceramide desaturase catalyzes formation of bioactive ceramide. 5) Ceramidase deacylates ceramide to form sphingosine and fatty acid. 6) Ceramide kinase phosphorylates ceramide to form ceramide 1-phosphate. 7) Glucosylceramide synthase adds glucose, an initial step in ganglioside formation. 8) Sphingomyelin synthase promotes the addition of phosphocholine to ceramide. 9) Sphingomyelinase regenerates ceramide and choline from the breakdown of sphingomyelin.