Structure and toxicity of pure ricinus agglutinin

Highly purified ricinus agglutinin was found to inhibit protein synthesis in HeLa cells. This effect could be prevented by the addition of the specific antiricinus agglutinin serum, whereas specific anti-ricin serum did not protect the cells, demonstrating that the toxic effect of ricinus agglutinin is not due to contamination with ricin. After reduction of ricinus agglutinin with 2-mercaptoethanol in the presence of 0.5 M galactose the constituent peptide chains were separated by chromatography on a DE-52 column. The B'-chain passed through the column, whereas the A'-chain bound and was eluted with a salt gradient. The B'-chain was further purified by chromatography on a CM-52 column. The shortest chain, the A'-chain, was found to inhibit cell-free protein synthesis whereas the B'-chain did not have this ability. On the other hand, the B'-chain was able to induce agglutination of erythrocytes when tested together with anti-ricinus agglutinin serum indicating that the "b'-chains bind to the cells. Ouchterlony immunodiffusion tests with crude anti-ricin and anti-ricinus agglutinin sera revealed that the two constituent chains of ricinus agglutinin are immunologically partial identical and that they also show reaction or partial identity with both chains of the toxic lectin ricin. The data indicate that a similar structure-function relationship exists in ricinus agglutinin as in ricin. The reason for the much lower toxicity of ricinus agglutinin than of ricin in living animals is discussed.