Golgi ceramidase that catalyzes the hydrolysis of ceramides into sphingoid bases like sphingosine and free fatty acids at alkaline pH (PubMed:16940153, PubMed:18945876, PubMed:20207939, PubMed:20089856). 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 (PubMed:20207939). Has a better catalytic efficiency towards unsaturated long-chain ceramides, including C18:1-, C20:1- and C24:1-ceramides (PubMed:16940153, PubMed:18945876, PubMed:20207939, PubMed:20089856). Saturated long-chain ceramides and unsaturated very long-chain ceramides are also good substrates, whereas saturated very long-chain ceramides and short-chain ceramides are poor substrates (PubMed:20089856). Also hydrolyzes dihydroceramides to produce dihydrosphingosine (PubMed:20207939, PubMed:20628055). It is the ceramidase that controls the levels of circulating sphingosine-1-phosphate and dihydrosphingosine-1-phosphate in plasma through their production by hematopoietic cells (By similarity). Regulates cell proliferation, autophagy and apoptosis by the production of sphingosine and sphingosine-1-phosphate (PubMed:16940153, PubMed:26943039, PubMed:28294157, PubMed:29229990). As part of a p53/TP53-dependent pathway, promotes for instance autophagy and apoptosis in response to DNA damage (PubMed:26943039, PubMed:28294157, PubMed:29229990). Through the production of sphingosine, may also regulate the function of the Golgi complex and regulate the glycosylation of proteins (PubMed:18945876). H2O + N-(15Z-tetracosenoyl)-sphing-4-enine = (15Z)-tetracosenoate + sphing-4-enine H2O + N-eicosanoyl-sphing-4-enine = eicosanoate + sphing-4-enine H2O + N-octadecanoylsphing-4-enine = octadecanoate + sphing-4-enine H2O + N-hexadecanoylsphing-4-enine = hexadecanoate + sphing-4-enine H2O + N-tetradecanoylsphing-4-enine = sphing-4-enine + tetradecanoate H2O + N-dodecanoylsphing-4-enine = dodecanoate + sphing-4-enine H2O + N-tetracosanoyl-sphing-4-enine = sphing-4-enine + tetracosanoate H2O + N-(hexanoyl)sphing-4-enine = hexanoate + sphing-4-enine H2O + N-(9Z-octadecenoyl)-sphing-4-enine = (9Z)-octadecenoate + sphing-4-enine an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine an N-acylsphinganine + H2O = a fatty acid + sphinganine Specifically activated by lumenal, but not cytosolic Ca(2+). Inhibited by Zn(2+) or Cu(2+). Mg(2+) or Mn(2+) have no effect on ceramidase activity (PubMed:20089856). Inhibited by De-MAPP (PubMed:20207939). Optimum pH is 7.5-9.0. Lipid metabolism; sphingolipid metabolism. Highly expressed in placenta. Up-regulated upon serum deprivation (PubMed:16940153). Up-regulated by N-(4-hydroxyphenyl)retinamode/4-HPR (PubMed:20628055). Up-regulated upon DNA damage, in a p53/TP53-dependent manner, resulting in increased levels of sphingosine and sphingosine-1-phosphate (at protein level) (PubMed:26943039, PubMed:28294157, PubMed:29229990). Belongs to the alkaline ceramidase family.