Binding of 125I-alpha toxin of Staphylococcus aureus to erythrocytes

Alpha toxin purified from Staphylococcus aureus strain Wood 46 and radioiodinated by the lactoperoxidase method retained full haemolytic activity and was used to study factors affecting binding to rabbit and horse erythrocytes. A relatively fixed percentage of added toxin bound to both cell types; the percentage bound was independent of temperature, pH, cell concentration and toxin concentration. Neither a 50-fold excess of native toxin nor Concanavalin A inhibited the binding of iodinated toxin to erythrocytes. The results suggest that differences in the sensitivity of erythrocytes to haemolysis do not reflect the abundance of high affinity toxin receptors on sensitive cells, but are more probably the result of differences in the intrinsic stability of the membrane and its sensitivity to perturbation by amphiphilic agents.