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. The bond between streptavidin and biotin is rapid and essentially non-reversible, unaffected by most extremes of pH, organic solvents, and denaturing reagents. It is the strongest known noncovalent biological interaction (Ka = 1015 M-1) between protein and ligand.
This conjugate recognizes streptavidin conjugates. MonoBiotin-ZAP (BT-ZAP) is a chemical conjugate of saporin labeled with biotin in a 1:1 chemically-determined average molar ratio. MonoBiotin-ZAP uses YOUR streptavidinylated targeting agent to target and eliminate cells.