title: Transport of ricin A chain after prior treatment of mouse leukemia cells with ricin B chain.
abstract: Ricin A chain acts to inhibit protein synthesis only if it penetrates the plasma membrane, and this requires the participation of the B chain. The two chains are held together in ricin by a single disulfide bond. In this paper, it is shown that the addition of A chain to mouse leukemia cells (AKR SL3) after the cells were first reacted with purified ricin B chain also results in efficient inhibition of protein synthesis. The data indicated that B chain bound to the cell surface was capable of causing the transport of A chain. The quantities of ricin and of B chain (in the presence of a saturating amount of A chain) required to inhibit protein synthesis by 50% are nearly identical, indicating that there is little difference in the toxicity to cultured cells between ricin and the A chain-B chain heterodimer formed from purified subunits. However, if the addition of A chain to B chain-treated cells was delayed sufficiently long (90 to 120 min), B chain was no longer able to cause A chain transport and the consequent inhibition of protein synthesis. Direct binding studies indicated that only a fraction of the bound 125I-B chain was internalized during this time. No proteolytic degradation of 125I-B chain could be detected after 3 h incubation with the cells.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D007942:Leukemia, Experimental / Q000378:metabolism*; D046911:Macromolecular Substances; D051379:Mice; D008854:Microscopy, Electron; D014176:Protein Biosynthesis; D012276:Ricin / Q000494:pharmacology*
chemical_list: D046911:Macromolecular Substances; D012276:Ricin