Endoplasmic reticulum ceramidase that catalyzes the hydrolysis of ceramides into sphingosine and free fatty acids at alkaline pH. Ceramides, sphingosine, and its phosphorylated form sphingosine-1-phosphate are bioactive lipids that mediate cellular signaling pathways regulating several biological processes including cell proliferation, apoptosis and differentiation. May also hydrolyze dihydroceramides to produce dihydrosphingosine. an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine H2O + N-tetracosanoyl-sphing-4-enine = sphing-4-enine + tetracosanoate an N-acylsphinganine + H2O = a fatty acid + sphinganine H2O + N-(9Z-octadecenoyl)-sphing-4-enine = (9Z)-octadecenoate + sphing-4-enine H2O + N-(15Z-tetracosenoyl)-sphing-4-enine = (15Z)-tetracosenoate + sphing-4-enine Lipid metabolism; sphingolipid metabolism. Belongs to the alkaline ceramidase family.