PAP2_like proteins, sphingosine-1-phosphatase subfamily. Sphingosine-1-phosphatase is an intracellular enzyme located in the endoplasmic reticulum, which regulates the level of sphingosine-1-phosphate (S1P), a bioactive lipid. S1P acts as a second messenger in the cell, and extracellularly by binding to G-protein coupled receptors of the endothelial differentiation gene family.