Saposins A-D localize primarily to the lysosomal compartment where they facilitate the catabolism of glycosphingolipids with short oligosaccharide groups.

[5] Saposins A–D are required for the hydrolysis of certain sphingolipids by specific lysosomal hydrolases.

[7] This helical structure is seen in all (especially with the first region), but saposin has been predicted to have β-sheet configuration due to it first 24 amino acids of the N-end.

[9] They probably act by isolating the lipid substrate from the membrane surroundings, thus making it more accessible to the soluble degradative enzymes.

The Saposin-B domains also occur in other proteins, many of them active in the lysis of membranes.