Saporin is obtained from the seeds of the Soapwort plant (Saponaria officinalis), a plant that grows wildly in Britain and other parts of Europe. Saporin is a plant enzyme with N-glycosidase activity that depurinates a specific nucleotide in the ribosomal RNA 28S, thus irreversibly blocking protein synthesis. It belongs to the well-characterized family of ribosome-inactivating proteins (RIPs). There are two types of RIPs: type I, which are much less cytotoxic due to the lack of the B chain and type II, which are distinguished from type I RIPs by the presence of the B chain and their ability to enter cells on their own. However, type I RIPs can still be internalized by fluid-phase endocytosis. Upon internalization, the ribosomes are inactivated, resulting in cell death.
Saporin (molecular weight 30 kDa) has no known specificity. Saporin is purified from the seeds of the Soapwort plant (Saponaria officinalis). The product is routinely tested for activity by a protein synthesis inhibition assay.
Saporin serves as a control for targeted saporin immunotoxins or ligand toxins.