Lysosomal ceramidase that hydrolyzes sphingolipid ceramides into sphingosine and free fatty acids at acidic pH (PubMed:10610716, PubMed:7744740, PubMed:15655246, PubMed:11451951). 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:10610716). Has a higher catalytic efficiency towards C12-ceramides versus other ceramides (PubMed:7744740, PubMed:15655246). Also catalyzes the reverse reaction allowing the synthesis of ceramides from fatty acids and sphingosine (PubMed:12764132, PubMed:12815059). For the reverse synthetic reaction, the natural sphingosine D-erythro isomer is more efficiently utilized as a substrate compared to D-erythro-dihydrosphingosine and D-erythro-phytosphingosine, while the fatty acids with chain lengths of 12 or 14 carbons are the most efficiently used (PubMed:12764132). Has also an N-acylethanolamine hydrolase activity (PubMed:15655246). By regulating the levels of ceramides, sphingosine and sphingosine-1-phosphate in the epidermis, mediates the calcium-induced differentiation of epidermal keratinocytes (PubMed:17713573). Also indirectly regulates tumor necrosis factor/TNF-induced apoptosis (By similarity). By regulating the intracellular balance between ceramides and sphingosine, in adrenocortical cells, probably also acts as a regulator of steroidogenesis (PubMed:22261821). May directly regulate steroidogenesis by binding the nuclear receptor NR5A1 and negatively regulating its transcriptional activity. an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine H2O + N-dodecanoylsphing-4-enine = dodecanoate + sphing-4-enine H2O + N-tetradecanoylsphing-4-enine = sphing-4-enine + tetradecanoate H2O + N-hexadecanoylsphing-4-enine = hexadecanoate + sphing-4-enine H2O + N-octadecanoylsphing-4-enine = octadecanoate + sphing-4-enine H2O + N-dodecanoyl-(4R)-hydroxysphinganine = (4R)-hydroxysphinganine + dodecanoate H2O + N-(dodecanoyl)-sphinganine = dodecanoate + sphinganine H2O + N-(acetyl)-sphing-4-enine = acetate + sphing-4-enine H2O + N-(hexanoyl)sphing-4-enine = hexanoate + sphing-4-enine H2O + N-octanoylsphing-4-enine = octanoate + sphing-4-enine H2O + N-(9Z-octadecenoyl)-sphing-4-enine = (9Z)-octadecenoate + sphing-4-enine H2O + N-dodecanoylethanolamine = dodecanoate + ethanolamine Activated by Ca(2+), Mg(2+) and Na(+) cations (PubMed:12764132). Inhibited by Zn(2+) (PubMed:12764132). Phosphatidylserine and phosphatidic acid stimulate while cardiolipin, phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and sphingomyelin inhibit the reverse ceramide synthase activity (PubMed:12764132). Phosphatidic acid, phosphatidylinositol and C16-ceramide inhibit the ceramidase/hydrolase activity (PubMed:12764132). Optimum pH is 3.8-5.0 for the hydrolysis of N-dodecanoylsphing-4-enine (PubMed:7744740, PubMed:12815059). Optimum pH is 5.5-6.5 for the synthesis of N-dodecanoylsphing-4-enine (PubMed:12815059). Lipid metabolism; sphingolipid metabolism. Heterodimer; disulfide-linked (PubMed:7744740, PubMed:11451951, PubMed:30525581, PubMed:29692406). The heterodimer is composed of the disulfide-linked alpha and beta chains produced by autocatalytic cleavage of the precursor (PubMed:7744740, PubMed:11451951, PubMed:30525581, PubMed:29692406). Isoform 2: May interact with NR5A1 in the nucleus; the direct interaction would negatively regulate NR5A1 transcriptional activity (Probable). Secretion is extremely low and localization to lysosomes is mannose-6-phosphate receptor-dependent. A localization to the nucleus and the cytoplasm has also been reported for ASAH1, most probably for isoforms devoid of a signal peptide. Broadly expressed with higher expression in heart. Up-regulated by Ca(2+). N-glycosylated. Proteolytically cleaved into two chains alpha and beta that remain associated via a disulfide bond (PubMed:7744740, PubMed:11451951, PubMed:30525581, PubMed:29692406). Cleavage gives rise to a conformation change that activates the enzyme. The same catalytic Cys residue mediates the autoproteolytic cleavage and subsequent hydrolysis of lipid substrates (PubMed:30525581, PubMed:29692406). The beta chain may undergo an additional C-terminal processing (PubMed:12815059). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Mutagenesis in position: 25:L->A (Loss of interaction with NR5A1). Belongs to the acid ceramidase family.