Structure and action of heteronemertine polypeptide toxins. Primary structure of Cerebratulus lacteus toxin B-IV.

The amino acid sequence of Cerebratulus toxin B-IV, a crustacean-selective axonal toxin occurring in the marine worm C. lacteus, was determined by Edman degradation of the tryptic and staphylococcal protease peptides obtained from the reduced, carboxymethylated toxin. All four of the anticipated maleylated tryptic peptides, ranging in size from 8 to 23 residues, and three staphylococcal protease peptides, ranging from 9 to 35 residues, were isolated in pure form by gel filtration followed by either ion exchange chromatography or preparative paper electrophoresis. The order of the maleylated tryptic peptides was based upon the sequences of the staphylococcal protease peptides. As might be expected, toxin B-IV displays no homology with the elapid nicotinic receptor toxins. In addition, toxin B-IV is structurally unrelated to a group of scorpion neurotoxins which, like B-IV, affect action potential generating mechanisms.