Lysosomal ceramidase that hydrolyzes sphingolipid ceramides into sphingosine and free fatty acids at acidic pH. an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine Lipid metabolism; sphingolipid metabolism. Heterodimer; disulfide-linked. The heterodimer is composed of the disulfide-linked alpha and beta chains produced by autocatalytic cleavage of the precursor. N-glycosylated. Proteolytically cleaved into two chains alpha and beta that remain associated via a disulfide bond. 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. The beta chain may undergo an additional C-terminal processing. Belongs to the acid ceramidase family.