The amino acid sequence of cobrotoxin

Abstract

Reduced S-carboxymethylated cobrotoxin was digested with trypsin and chymotrypsin. Nine peptides were isolated from the tryptic digest by a combination of electrophoresis and chromatography on paper. The amino acid sequence in these peptides was determined by applying the Edman degradation and by using proteolytic enzymes, leucine aminopeptidase and carboxypeptidases. The arrangement of nine peptides in a linear structure was determined by comparing the amino acid compositions of the overlapping peptides isolated from the chymotryptic digest of reduced S-carboxymethylated cobrotoxin. The striking distributional regularities of the basic and hydrophilic residues in the sequence and the importance of the positions of half cystinyl residues which form the disulfide bonds for maintaining the protein in its active configuration, are considered in connection with the structure-activity relationship of the protein.