EFFECT OF TEMPERATURE ON THE UPTAKE, EXCRETION AND DEGRADATION OF ABRIN AND RICIN BY HELA-CELLS

The effect of temperature on the uptake of abrin and ricin and on the subsequent excretion and degradation of the toxins was measured. Uptake was assessed either by monitoring the amount of cell-bound 125I-labelled toxin that could not be released with lactose or by measuring the time required for transport of the toxins into a state where they were protected against neutralizing antibodies. The presence of toxin in this state was monitored by measuring inhibition of protein synthesis after a subsequent prolonged incubation period. In the case of abrin, straight lines were found in both cases when the data were plotted according to Arrhenius. The activation energies estimated was 18-21 kcal/mol (75-88 kJ/mol) in the case of uptake of [125I]abrin and 15-19 kcal/mol (63-79 kJ/mol) when the indirect method was used. After internalization of [125I]abrin and ricin a fraction of the radioactive material is released to the medium. Most of this material can be precipitated by trichloroacetic acid (TCA). There is a rapid release during the first 30 min and then over the next few hours the release occurs at a constant, but lower rate. The release of ricin was not affected by addition of colchicine, cytochalasin B (CB), ammonium chloride, sodium azide or bovine serum albumin, whereas the degradation of ricin was reduced by the above mentioned compounds (except albumin). The release of ricin was strongly temperature-dependent with a sharp transition at about 20 °C. The activation energies for the release above and below 20 °C were found to be 2.5 and 31 kcal/mol (10.5 and 172 kJ/mol), respectively. © 1979.