Binding characteristics of a sea anemone toxin from Parasicyonis actinostoloides with crayfish leg nerves.

A sea anemone toxin from Parasicyonis actinostoloides which inhibits the inactivation process of the sodium channel was acylated by using cold or tritium labeled propionyl N-hydroxysuccinimide ester. Acylation changed the isoelectric point of the peptide but did not change the toxicity to the crayfish nerve. Propionyl-toxin bound to leg nerves with Kd of 310 nM and Bmax of 104 pmol/g of wet nerve. The binding affinity and physiological activity of the toxin to crayfish nerves were suppressed with a common dependence on membrane depolarizations induced by elevated external K+ concentrations.