The Binding of Abrin and Ricin by Ehrlich Ascites Tumor Cells

Abrin and ricin cause 50% agglutination of Ehrlich ascites tumor cells (5*10⁶/ml) at a concentration of 8 and 4 μg/ml, respectively. Addition of D-galactose or its derivatives, lactose or raffinose, inhibits the agglutinating activity of the toxic proteins. Binding of ¹³ I-toxic proteins on the tumor cells was shown to be specific, pH dependent, and concentration dependent. Native ricin, abrin, D-galactose, and its sterically related saccharides inhibit this specific binding, while concanavalin A, bovine serum albumin, heat-denatured abrin or ricin, and other saccharides do not. In the presence of D-galactose, the inhibition of protein biosynthesis by ricin does not occur in vitro.