Hybrid toxin of the A chain of ricin toxin and a subunit of Wistaria floribunda lectin. Possible importance of the hydrophobic region for entry of toxin into the cell.

About 27% or more of the total amount of the A chain of ricin toxin associated with lipid vesicles, whereas less than 1.4% of the A fragment of diphtheria toxin associated with the vesicles under the various conditions tested. Two hybrid toxins were constituted from a subunit of Wistaria floribunda lectin and the A fragment of diphtheria toxin (Uchida, Y., Yamaizumi, M., Mekada, E., Okada, Y., Tsuda, M., Kurokawa, T., and Sugino, Y. (1978) J. Biol. Chem. 253, 6307-6310) and the A chain of ricin toxin, which has higher affinity to lipids than the A fragment of diphtheria toxin. The toxicity of the hybrid of the A chain of ricin and the subunit of W. floribunda lectin, estimated by measuring the inhibition of protein synthesis of cultured cells, was about 100 to 200 times that of the hybrid of the A fragment of diphtheria and the subunit of W. floribunda lectin. These findings may suggest that a hydrophobic region of the toxin is essential for entry of toxin into the cells.