Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sphingosine kinase 1 is an enzyme that in humans is encoded by the SPHK1 gene. Sphingosine kinase 1 phosphorylates sphingosine to sphingosine-1-phosphate (S1P) SK1 is normally a cytosolic protein but is recruited to membranes rich in phosphatidate (PA), a product of Phospholipase D (PLD). Sphingosine-1-phosphate (SPP) is a novel lipid messenger with both intracellular and extracellular functions. Intracellularly, it regulates proliferation and survival, and extracellularly, it is a ligand for EDG1. Various stimuli increase cellular levels of SPP by activation of sphingosine kinase (SPHK), the enzyme that catalyzes the phosphorylation of sphingosine.