Background：Saposin-A and saposin-C stimulate the hydrolysis of glucosylceramide by beta-glucosylceramidase(EC 3.2.1.45) and galactosylceramide by beta-galactosylceramidase(EC 3.2.1.46). Saposin-C apparently acts by combining with the enzyme and acidic lipid to form an activated complex, rather than by solubilizing the substrate.
Saposin-B stimulates the hydrolysis of galacto-cerebroside sulfate by arylsulfatase A(EC 3.1.6.8), GM1 gangliosides by beta-galactosidase(EC 3.2.1.23) and globotriaosylceramide by alpha-galactosidase A(EC 3.2.1.22). Saposin-B forms a solubilizing complex with the substrates of the sphingolipid hydrolases.
Saposin-D is a specific sphingomyelin phosphodiesterase activator(EC 3.1.4.12).
Prosaposin: Behaves as a myelinotrophic and neurotrophic factor, these effects are mediated by its G-protein-coupled receptors, GPR37 and GPR37L1, undergoing ligand-mediated internalization followed by ERK phosphorylation signaling.
Saposins are specific low-molecular mass non-enzymic proteins, they participate in the lysosomal degradation of sphingolipids, which takes place by the sequential action of specific hydrolases.
