Hydrolyzes the sphingolipid ceramide into sphingosine and free fatty acid. an N-acylsphing-4-enine + H2O = a fatty acid + sphing-4-enine Expressed in the central midgut of late embryos. In brain, it is present at the interhemispheric junction and in groups of cells in the central brain. Discrete defect in the ellipsoid body. Belongs to the alkaline ceramidase family.