A weak reversibly acting neurotoxin, fasciatoxin, was found in the venom of Bungarus fasciatus. The sequencing was completed by manual and automated Edman analyses of the reduced and carboxymethylated protein and of the peptides obtained from enzyme digestions. It is composed of 63 amino acid residues with four disulphide bonds and a unique sequence at the C-terminal end. According to the criteria set by Ryden, Gabel & Eaker [(1973) Int. J. Pept. Protein Res. 5, 261-273], fasciatoxin lacks all of the five functionally invariant residues of neurotoxins. The hydropathy index indicates that fasciatoxin is devoid of a strong hydrophilicity domain for binding to the receptor site. Structural comparison with some typical neurotoxins also reveals the uniqueness of fasciatoxin in that the extent of similarity is only about 30%.
The amino acid sequence of a short chain neurotoxin obtained from Bungarus fasciatus venom consists of 64 amino acid residues: Arg-Ile-Cys-Leu-Asn-Gln-Gln-Gln-Ser- Thr-Pro-Glu-Asp-Gln-Pro-Thr-Asn-Gly-Gln-Cys-Tyr-Ile-Lys-Thr-Asp-Cys-Gln- Asn-Lys - Thr-Trp-Asn-Thr-His-Arg-Gly-Ser-Arg-Thr-Asp-Arg-Gly-Cys-Gly-Cys-Pro-Lys- Val-Lys - Pro-Gly-Ile-Asn-Leu-Arg-Cys-Cys-Lys-Thr-Asp-Lys-Cys-Asn-Glu. The above result was obtained primarily from the amino acid analyses and sequencing of tryptic peptides accompanied with the necessary analyses and sequencing of the chymotryptic and lysyl endopeptidic peptides for alignment.
Two phospholipases were found in the venom of Bungarus fasciatus, one in fraction III, the other in fraction X of the chromatographic separation. A neutral PLA2(III) purified from fraction III was subjected to amino acid sequencing by means of an automated sequenator applied to the intact RCM‐PLA2 (III) and the individual peptides obtained from HPLC separation of the three types of enzymatic peptides. PLA(III) was shown to consist of 118 amino acid residues with 14 half‐cystines. It is 65% homologous to the basic PLA2 obtained from fraction X.
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