Interaction between sphingomyelin and a cytolysin from the sea anemone Stoichactis helianthus

The cytolytic toxin from the sea anemone Stoichactis helianthus was inhibited up to 90--95% by suspensions of sphingomyelin but not by phosphatidylcholine or other membrane lipids. When the toxin was incubated with sphingomyelin and the mixture fractionated either by isoelectric focusing or Sephadex gel filtration, the residual hemolytic units migrated together with the lipid and not as free toxin. Incubation with phosphatidylcholine, however, did not shift the toxin peak in either type of column. A toxin-ferritin conjugate retaining hemolytic activity was observed by negative staining to bind to liposomes prepared with sphingomyelin but not with liposomes containing phosphatidylcholine. The results provide evidence that the membrane binding site of the toxin is sphingomyelin.