Sphingolipids are important membrane signalling molecules involved in many different cellular functions in eukaryotes. Sphingolipid delta 4-desaturase catalyzes the formation of (E)-sphing-4-enine. Some proteins in this family have bifunctional delta 4-desaturase/C-4-hydroxylase activity. Delta 4-desaturated sphingolipids may play a role in early signalling required for entry into meiotic and spermatid differentiation pathways during Drosophila spermatogenesis. This small domain associates with FA_desaturase pfam00487 and appears to be specific to sphingolipid delta 4-desaturase.