Plasma membrane ceramidase that hydrolyzes sphingolipid ceramides into sphingosine and free fatty acids at neutral pH (PubMed:10753931, PubMed:10652340, PubMed:16380386). 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:14557071). Also catalyzes the reverse reaction allowing the synthesis of ceramides from fatty acids and sphingosine (PubMed:10652340, PubMed:21613224). Together with sphingomyelinase, participates in the production of sphingosine and sphingosine-1-phosphate from the degradation of sphingomyelin, a sphingolipid enriched in the plasma membrane of cells (PubMed:16126722). Also participates in the hydrolysis of ceramides from the extracellular milieu allowing the production of sphingosine-1-phosphate inside and outside cells (PubMed:16126722). This is the case for instance with the digestion of dietary sphingolipids in the intestinal tract (PubMed:16380386). an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine H2O + N-hexadecanoylsphing-4-enine = hexadecanoate + sphing-4-enine H2O + N-dodecanoylsphing-4-enine = dodecanoate + sphing-4-enine H2O + N-octadecanoylsphing-4-enine = octadecanoate + sphing-4-enine H2O + N-octanoylsphing-4-enine = octanoate + sphing-4-enine H2O + N-(hexanoyl)sphing-4-enine = hexanoate + sphing-4-enine H2O + N-tetradecanoylsphing-4-enine = sphing-4-enine + tetradecanoate H2O + N-(9Z-octadecenoyl)-sphing-4-enine = (9Z)-octadecenoate + sphing-4-enine H2O + N-(15Z-tetracosenoyl)-sphing-4-enine = (15Z)-tetracosenoate + sphing-4-enine hexadecanoate + sphinganine = H2O + N-hexadecanoylsphinganine H2O + N-(octadecanoyl)-sphinganine = octadecanoate + sphinganine Binds 1 zinc ion per subunit. Inhibited by D-erythro-MAPP. Optimum pH is 7.5. Lipid metabolism; sphingolipid metabolism. May interact with CAV1. Enriched in exosomes upon stimulation by cytokine (By similarity). Enriched in caveolae and lipid rafts (PubMed:12921776). Widely expressed (PubMed:10753931, PubMed:14557071). Strongly expressed in small intestine and to a lower extent in liver and kidney (PubMed:10753931). Highly expressed in duodenum, jejunum and ileum along the brush border of the small intestine (at protein level) (PubMed:16380386). Proteolytic cleavage of the N-terminus removes the signal-anchor and produces a soluble form of the protein. N-glycosylated. Required for enzyme activity. O-glycosylated. Required to retain it as a type II membrane protein at the cell surface. Phosphorylated. May prevent ubiquitination and subsequent degradation. Ubiquitinated, leading to its degradation by the proteasome. Ubiquitination is triggered by nitric oxide. Homozygous knockout mice have a normal life span and do not show obvious abnormalities or major alterations in total ceramide levels in tissues (PubMed:16380386). However, they are deficient in the intestinal digestion of dietary ceramides (PubMed:16380386). A decrease in total ceramides in liver is also observed (PubMed:21613224). Belongs to the neutral ceramidase family.