Complete amino acid sequences of two cardiotoxin-like analogues from Bungarus fasciatus (banded krait) snake venom

Three cardiotoxin-like proteins have been isolated from Bungarus fasciatus venom and the amino acid sequence of the major toxin (toxin VI) have been determined. The amino acid sequences of two other analogues (toxins V-2 and V-3) were investigated. The reduced and S-carboxymethylated toxins were digested with trypsin-TPCK and the resulting tryptic peptides were isolated by fingerprinting technique on paper. The amino acid compositions, N-terminal residues and partial amino acid sequences of some of the tryptic peptides were determined. Thirteen tryptic peptides were aligned by following the order of corresponding fragments of toxin VI. Toxins V-2 and V-3 contained 118 and 117 amino acid residues, respectively, in a single polypeptide chain cross-linked with six pairs of intramolecular disulphide bonds. There are only four (for toxin V-2) and five (for toxin V-3) places of differences in their primary structures when compared with that of the major toxin (toxin VI) of Bungarus fasciatus venom.