Chemical Studies on the Poison of Formosan Cobra. III

Amino Acid Composition of Purified Poison (Neurotoxin)

Abstract

Poisonous component of Formosan cobra (Naja naja atra) was purified by acetone and ammonium sulfate to obtain a neurotoxin and its hydrolyzate with hydrochloric acid was submitted to two-dimensional chromatography and paper electrophoresis, from which 13 kinds of amino acid were detected. Since neurotoxin is positive to the Adamkiewitz reaction, it is known to contain tryptophan. Results of these determinations of amino acid are listed in Table I. As will be clear from this Table, neurotoxin contains a large amount of threonine, glycine, aspartic acid, glutamic acid, and arginine. It has been shown in the preceding paper that neurotoxin contains leucine as the N-terminal amino acid and glyine as the C-terminal amino acid in an unbranched polypeptide chain. From the quantitative determination of amino acids, this peptide is thought to be composed of 50 amino acid residues and its minimum molecular weight would be around 6000, while the presence of cystine, either as the terminal amino acid or in the peptide chain with free carboxyl, is denied. From these results, structural formulae presented in Figs. 1 and 2 are proposed for neurotoxin. The fact that neurotoxin can pass through ordinary cellophane membrane suggests that its true molecular weight would not be so large and the lysozyme-type structure with molecular weight of about 6000, as given in Fig. 1, seems to be the most appropriate.