Binding and cytotoxicity of Ricinus communis lectins to HeLa cells, Sarcoma 180 ascites tumor cells and erythrocytes

The binding of Ricinus communis lectins to HeLa cells, Sarcoma 180 ascites tumor cells and human erythrocytes was studied in detail. Scatchard plots of binding of 125I-lectins to these cells gave biphasic lines except for HeLa cells at 0 degree C. The association constants of lectins for the three cell types at 37 degrees C were lower than those at 0 degree C. The numbers of total binding sites were estimated to be 7 to 16 X 10(7) per HeLa cell, 3 to 4 X 10(7) per Sarcoma 180 ascites tumor cell and 0.4 to 1 X 10(6) per erythrocyte. A fraction, 16 to 27% of the total amount of cell-bound lectin at 37 degrees C, appeared to be bound irreversibly as judged by non-removal on washing with 0.1 M lactose, whereas no lectin was irreversibly bound at 0 degree C. In the case of erythrocytes, no lectin became irreversibly bound even at 37 degrees C. The toxicity of lectins on HeLa cells and Sarcoma 180 ascites tumor cells was investigated. The toxicity of ricin D was 50 times for Sarcoma 180 ascites tumor cells and 140 times for HeLa cells as much as that for castor bean hemagglutinin. As to the sensitivities of both cell types to these lectins, it became apparent that Sarcoma 180 ascites tumor cells were more susceptible than HeLa cells.