Table 1.

Key pathways of sphingolipid metabolism.

Pathways and Reactions of Ceramide Metabolism	Rate-Limiting Enzyme	Site of Production and Location	Other Main Involved Enzymes
De novo synthesis pathway	Serine palmitoyltransferase (SPT)	Endoplasmic reticulum	3-keto-sphingosine reductase Ceramide synthase (CerS) Dihydroceramide desaturase (Des1/DEGS1)
Sphingomyelinase pathway	Sphingomyelinases (Smases)	Plasma membrane; lysosomes	Sphingomyelin synthase (SMS)
Salvage pathway	Ceramide synthase (CerS)	Endo/lysosomes; mitochondria	Glucosylceramide synthase (GCS) Acid β-Glucosidase (β-GCase) Ceramidase
Ceramide kinase and ceramide 1 phosphate			Ceramide phosphate phosphatases (CPP)
Sphingosine kinase (SphK)/S1P phosphatase			Sphingosine kinase (SphK) Sphingosine 1-Phosphate Phosphatase (SPP) Lipid phosphate phosphatase (LPP)