Alkaline ceramidase that hydrolyzes phytoceramide and also dihydroceramide into phytosphingosine or dihydrosphingosine. Prefers phytoceramide. Has also reverse activity as acyl-CoA-independent ceramide synthase, catalyzing synthesis of phytoceramide and dihydroceramide from palmitic acid and phytosphingosine or dihydrosphingosine. Is not responsible for the breakdown of unsaturated ceramide (PubMed:10702247, PubMed:10900202, PubMed:11694577, PubMed:24866405). Preferentially uses very long chain fatty acids (C-24 and C-26) in vivo compared to C-16 in vitro (PubMed:24866405). H2O + N-hexanoyl-sphinganine = hexanoate + sphinganine hexadecanoate + sphinganine = H2O + N-hexadecanoylsphinganine H2O + N-hexadecanoyl-(4R)-hydroxysphinganine = (4R)-hydroxysphinganine + hexadecanoate H2O + N-hexadecanoylsphing-4-enine = hexadecanoate + sphing-4-enine an N-acyl-(4R)-4-hydroxysphinganine + H2O = (4R)-hydroxysphinganine + a fatty acid Localizes to the cortical ER. Belongs to the alkaline ceramidase family.