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 cleaved by sphingosine phosphatase. S1P is a blood borne lipid mediator, in particular in association with lipoproteins such as high density lipoprotein (HDL). It is less abundant in tissue fluids. This is referred to as the S1P gradient which seems to have biological significance in immune cell trafficking.
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