Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sphingosine-1-phosphate (S1P) is a signaling sphingolipid. It is also referred to as a bioactive lipid mediator. Sphingolipids at large form a class of lipids characterized by a particular aliphatic aminoalcohol, which is sphingosine. Sphingosine can be released from ceramides, a process catalyzed by the enzyme ceramidase. Phosphorylation of sphingosine is catalyzed by sphingosine kinase, an enzyme ubiquitously found in the cytosol and endoplasmatic reticulum of various types of cells. S1P can be dephosphorylated to sphingosine by sphingosine phosphatases and can be irreversibly degraded by an enzyme, Sphingosine phosphate lyase.