The role of lysine, histidine and carboxyl residues in biological activity of equinatoxin II, a pore forming polypeptide from the sea anemone Actinia equina L.

Equinatoxin II, a pore forming polypeptide from the sea anemone Actinia equina L. was subjected to chemical modifications with group specific reagents. Lysine residues were modified with pyridoxal-5'-phosphate, histidine residues with diethyl pyrocarbonate and carboxyl groups with the use of a water soluble carbodiimide. Modification of charged residues had no significant influence on the toxin interaction with serum lipoproteins. Lysine 5'-phosphopyridoxylated and histidine carbethoxylated derivatives of the toxin retained lethal and hemolytic activities, but the pH profile of hemolytic activity of 5'-phospho-pyridoxylequinatoxin II was markedly altered. Modification of the toxin carboxyl groups impaired both hemolytic and lethal activities, the latter, however, to the greater extent.