FIG. 3.

AC toxin renatured in the presence of calcium before addition to sheep RBC in EDTA binds to cells but at a reduced level. Sheep RBC were washed and resuspended in buffer A containing 2 mM EDTA or buffer A containing 3.2 mM calcium. AC toxin (10 μg/ml) was added to RBC as indicated below for 30 min at 37°C. Solid line, toxin renatured in the presence of EDTA upon its addition to cells in buffer A containing 2 mM EDTA; dotted line, AC toxin renatured in the presence of calcium as described in Materials and Methods but incubated with sheep RBC in buffer A containing EDTA; bold solid line, AC toxin renatured in the presence of calcium upon its addition to RBC in buffer A containing 3.2 mM calcium. Data are representative of five separate experiments.