[Ricin, the toxic protein of the castor-oil plant (Ricinus communis L). Structure and properties (author's transl)].

Ricin is an extremely toxic phytotoxin from the castor-oil plant seeds. This toxin is different from the two phyto-hemagglutinins or lectins which are also present in the seeds and can be purified in two chromatographic steps. Studies on the physical and chemical properties of pure ricin are given (molecular weight: 65 750 daltons, glycoproteic nature, oses composition: 15 moles of mannose and 8 moles of N-acetyl-glucosamine per mole of ricin, aminoacids composition: 545, bicatenary structure: the toxin is formed by two polypeptide A and B chains linked together by a disulfure bond). Though ricin is resistant to proteolytic enzymes under normal conditions, we have found conditions in which tryptic hydrolysis of the toxin gives several peptides which retain toxicity. Two of them were purified. The LD50 on mice of ricin and its isolated toxic peptides were determined, the symptoms of ricin's intoxication were established on animals which died from a dramatic hepatonephritic injury, but always after a lag. Ricin has a cytostatic, and then a cytotoxic effect on cells in culture which are highly damaged (important membranous protrusions). The mechanism of ricin's action was studied. It inhibits elongation in protein synthesis in vivo as well as in vitro, by acting on ribosomes whether cytoplasmic, mitochondrial or chloroplastic. To act, the ricin A-chain must be activated by ribosomes which split the ricin molecule into its polypeptide chains; these ribosomes are then frozen by the toxin and became inefficients in protein synthesis.