TOXICITY AND CYTOTOXICITY OF NIGRIN-B, A 2-CHAIN RIBOSOME-INACTIVATING PROTEIN FROM SAMBUCUS-NIGRA - COMPARISON WITH RICIN

Nigrin b, a lectin isolated from the bark of elderberry (Sambucus nigr a L.), has structure and enzymatic activity similar to that of ricin a nd other type 2 ribosome-inactivating proteins (RIPs), and yet is much less toxic to cells and animals. III an attempt to explain this diffe rence, we studied (1) the cytotoxicity of both lectins at 18 and 37 de grees C: and in the presence of substances interfering with intracellu lar routing, and (2) the binding of nigrin b to, and its uptake and de gradation by HeLa cells, in parallel with ricin. As compared with the latter, (1) less nigrin b was bound and more was degraded by cells, wi th a resulting lower concentration remaining inside the cells, and (2) there is evidence for a different intracellular routing followed by t he two lectins. These results may explain at least partly the differen t cytotoxicity and consequently the lower toxicity to mice of nigrin b compared with ricin.