Fig. 1. Effect of thapsigargin on the sulfation of (A) ricin sulf-2 and (B) STxB-Sulf₂. MDCK II cells were incubated with radioactive sulfate for 3 hours at 37°C, and during the last 30 minutes thapsigargin was added. Then ricin sulf-2 (200 ng/ml) (A) or STxB-Sulf₂ (2.8 µg/ml) (B) was added to the medium and the incubation was continued for 2 hours. The cells were subsequently washed, lysed and immunoprecipitated with rabbit anti-ricin antibodies (A) or rabbit anti-Shiga toxin antibodies (B). The adsorbed material was analyzed by SDS-PAGE (12%) before autoradiography (details in Materials and Methods).