Erabutoxin c, a minor neurotoxic component of the venom of a sea snake Laticauda 
semifasciata, was isolated in pure form by repeated column chromatography on 
CM-cellulose columns. The toxin was crystallizable and monodisperse in 
rechromatography, disc electrophoresis and isoelectric focusing (isoelectric 
point, pH9.23-9.25). The molecular weight of the toxin, as estimated by gel 
filtration, was 7000. The toxin showed the same lethal activity to mice 
(0.13mug/g body wt., intramuscular injection) and the same effect on isolated 
frog muscle as erabutoxins a and b, the main toxic components of the venom. The 
toxin inhibited the acetylcholine contracture but not the potassium chloride 
contracture of muscle. Erabutoxin c consisted of 62 amino acid residues, 
containing one fewer lysine and one more histidine than erabutoxin a and one 
fewer lysine and one more aspartic acid (or asparagine) than erabutoxin b. 
Erabutoxin c was reduced, S-carboxymethylated and hydrolysed with trypsin. The 
only fragment different from the corresponding fragments from erabutoxin b was 
hydrolysed further with pepsin. One of the peptic fragments, which was assumed 
to have the aspartic acid (or asparagine) residue in question at the C-terminal 
end, was treated with carboxypeptidase A. The C-terminal residue was found to be 
an asparagine. It was therefore concluded that erabutoxin c was 
[51-asparagine]-erabutoxin b.