Interaction between ricin and Zajdela ascitic hepatoma cells

The binding to and toxicity of ricin on Zajdela hepatoma ascites cells were studied. The kinetic analysis of 125I]-ricin binding to hepatoma cells indicated that maximal specific binding was reached within 30 min. at 4 degrees C and 60 min. at 25 degrees C and that toxin binding to hepatoma cells was saturable. When the binding data were plotted according to the method of Scatchard, curvilinear graphs were obtained suggesting that hepatoma cells have both high and low affinity receptors for ricin. The number of high and low affinity receptors was identical at 4 and 25 degrees C, i.e., 8 x 10(5) and 1.2 x 10(7) sites per cell respectively. However, the capacity of hepatoma cells to bind ricin is stronger at 4 degrees C than at 25 degrees C. The toxic activity of ricin was totally abolished in the presence of lactose suggesting that ricin binding to cells occurs through binding sites containing galactosyl residues.