Plasma membrane ceramidase that hydrolyzes sphingolipid ceramides into sphingosine and free fatty acids at neutral pH (PubMed:10781606, PubMed:16229686, PubMed:26190575). 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:15946935, PubMed:19345744, PubMed:24798654). Also catalyzes the reverse reaction allowing the synthesis of ceramides from fatty acids and sphingosine (PubMed:11278489, PubMed:17475390). 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:16061940). Also participates in the hydrolysis of ceramides from the extracellular milieu allowing the production of sphingosine-1-phosphate inside and outside cells (By similarity). This is the case for instance with the digestion of dietary sphingolipids in the intestinal tract (By similarity). an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine H2O + N-dodecanoylsphing-4-enine = dodecanoate + sphing-4-enine H2O + N-hexadecanoylsphing-4-enine = hexadecanoate + sphing-4-enine H2O + N-octanoylsphing-4-enine = octanoate + sphing-4-enine H2O + N-(hexanoyl)sphing-4-enine = hexanoate + sphing-4-enine H2O + N-octadecanoylsphing-4-enine = octadecanoate + 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 dithiothreitol (DTT) and 2-mercaptoethanol (PubMed:16229686). Activity is mildly stimulated by Ca(2+) and Mg(2+), but is not inhibited by EDTA (PubMed:10781606, PubMed:16229686). Activity is inhibited by millimolar levels of Fe(2+), Zn(2+) and Cu(2+) (PubMed:16229686, PubMed:17475390). Inhibited by cholesterol (PubMed:17475390). Optimum pH is 7.5-9.5 for N-hexadecanoylsphing-4-enine (PubMed:10781606). Optimum pH is 7.5 for D-erythro-C12-NBD-ceramide (PubMed:16229686). Optimum pH is 7.5 for N-octanoylsphing-4-enine (PubMed:17475390). Lipid metabolism; sphingolipid metabolism. Enriched in exosomes upon stimulation by cytokine (PubMed:24798654). Enriched in caveolae and lipid rafts (By similarity). The localization to the mitochondrion could not be confirmed (PubMed:15845354). Primarily expressed in intestine (PubMed:17334805). Ubiquitously expressed with higher levels in kidney, skeletal muscle and heart (PubMed:10781606). The ubiquitous expression observed for ASAH2 might be an experimental artifact due to the paralog ASAH2B (PubMed:17334805). Down-regulated by gemcitabine/GMZ (at protein level) (PubMed:19345744). Down-regulated upon serum starvation (PubMed:19345744). 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. Belongs to the neutral ceramidase family. Was proposed to be mitochondrial, based on experiments with an N-terminal GFP-tag (PubMed:10781606). The in vivo localization to the mitochondrion could not be confirmed (PubMed:15845354). However, it has been observed for the mouse (AC Q9JHE3) and rat (AC Q91XT9) orthologs. Truncated N-terminus.