Snake venom toxins The isolation and purification of three cytotoxin homologues from the venom of the forest cobra ( Naja melanoleuca) and the complete amino acid sequence of toxin V II1

Abstract

Three proteins (V II1–V II3) have been isolated from the venom of Naja melanoleuca (Forest cobra). The complete amino acid sequence of V II1 has been established. The sequence of V II1 and the amino acid composition and other data for V II2 and V II3 indicate that the three proteins are homologoes of the cyto- or cardiotoxins which have been isolated from the venoms of other members of the Elapidae sub-family. Protein V II1 showed the intravenous toxicity level typical of cytotoxin type proteins, while V II2 and V II3 were considerably less toxic. The sequence of the first 34 residues, out of the total of 60, was determined using an automatic sequenator. The remaining 26 residues were aligned with the aid of tryptic and chymotryptic peptides and thermolysin produced sub-fragments of one tryptic peptide. It was found that V II1 consisted of a pair of isoproteins having leucine and isoleucine NH 2-terminal residues.