Endoplasmic reticulum ceramidase that catalyzes the hydrolysis of ceramides into sphingosine and free fatty acids at alkaline pH (PubMed:12783875). 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:12783875). Exhibits a strong substrate specificity towards the natural stereoisomer of ceramides with D-erythro-sphingosine as a backbone and has a higher activity towards very long-chain unsaturated fatty acids like the C24:1-ceramide (PubMed:12783875). May also hydrolyze dihydroceramides to produce dihydrosphingosine (By similarity). ACER1 is a skin-specific ceramidase that regulates the levels of ceramides, sphingosine and sphingosine-1-phosphate in the epidermis, mediates the calcium-induced differentiation of epidermal keratinocytes and more generally plays an important role in skin homeostasis (PubMed:27126290, PubMed:29056331). 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 Inhibited by sphingosine (PubMed:12783875). Inhibited by Mn(2+), Zn(2+), and Cu(2+) in a dose-dependent manner (PubMed:12783875). Slightly activated by Ca(2+) in a dose-dependent manner (PubMed:12783875). Optimum pH is 8.0. Lipid metabolism; sphingolipid metabolism. Highly expressed in skin. Weakly or not expressed in other tissues (PubMed:12783875). Expressed by granular layer of interfollicular epidermis, sebaceous glands and infundibulum (PubMed:29056331). Homozygous knockout mice are viable and fertile, with a normal lifespan but display several postnatal skin phenotypes (PubMed:27126290, PubMed:29056331). It includes an increase in total ceramide levels in the dorsal skin, tail epidermis and dermis (PubMed:27126290, PubMed:29056331). This is associated with hair shafts and sebaceous glands abnormalities, cyclic alopecia, a progressive loss of hair follicle stem cells, hyperproliferation, inflammation and abnormal differentiation of the epidermis and results in increased transepidermal water loss and reduction of fat content during aging (PubMed:27126290, PubMed:29056331). Belongs to the alkaline ceramidase family.