Title: Bungarotoxins
Literature References: Constituent proteins of the venom of the Elapidae snake, Bungarus multicinctus (Southeast Asian banded krait). Separation of the crude venom yields several fractions, the most important being a-bungarotoxin (a-Bgt) and b-bungarotoxin (b-BuTX): C. C. Chang, C. Y. Lee, Arch. Int. Pharmacodyn. Ther. 144, 241 (1963). a-Bgt is a single polypeptide chain of mol wt about 8,000 containing 74 amino acid residues with 5 disulfide bridges: D. Mebs et al., Biochem. Biophys. Res. Commun. 44, 711 (1971); eidem, Z. Physiol. Chem. 353, 243 (1972). Purification, characterization, immunochemical studies: D. G. Clark et al., Biochemistry 11, 1663 (1972). It is a post-synaptic neurotoxin with curare-like action that binds irreversibly to acetylcholine receptor sites, producing neuromuscular blockade and skeletal muscle paralysis. Activity and use as a probe for acetylcholine receptors: C. C. Chang, Nature 215, 1177 (1967); J. P. Changeux et al., Proc. Natl. Acad. Sci. USA 67, 1241 (1970); R. E. Oswald, J. A. Freeman, Neuroscience 6, 1 (1981). b-Bungarotoxin has been shown to contain several components, the major protein being designated as b1- or b-bungarotoxin. It is composed of 2 subunits of mol wts of about 13,000 and 7,000, linked by disulfide bonds. The larger chain contains 120 amino acid residues including 13 half-cystine; the smaller chain contains 60 residues including 7 half cystine. Purification: T. Abe et al., Eur. J. Biochem. 80, 1 (1977); eidem, Proc. R. Soc. London Ser. B 207, 487 (1980). Chemical properties, and amino acid sequence of the two polypeptide chains: K. Kondo et al., J. Biochem. 83, 91, 101 (1978). Complete purification and characterization of its action on synaptosomal accumulation and release of acetylcholine: J. W. Spokes, J. O. Dolly, Biochim. Biophys. Acta 596, 81 (1980). b-BuTX is a pre-synaptic neurotoxin that prevents acetylcholine release at skeletal neuromuscular junctions without affecting the sensitivity of the post-synaptic membrane. Its proposed phospholipase A2 activity is believed to be responsible for some of its effects at motor nerve terminals. Activity studies: P. N. Strong et al., Proc. Natl. Acad. Sci. USA 75, 1029 (1976); T. Abe, R. Miledi, Proc. R. Soc. London Ser. B 200, 225 (1978); M. T. Alderdice, R. L. Volle, Arch. Pharmacol. 316, 126 (1981). Review: A. T. Tu, Venoms: Chemistry and Molecular Biology (Wiley, New York, 1977) pp 185-187, 240-251.
Properties: The crude venom of Bungarus multicinctus is quite toxic, having an LD50 in mice (mg/g): 0.16 s.c. (Chang, Lee); also reported as 0.33 s.c. (Mebs, 1972). LD50 of a-Bgt in mice (mg/g): 0.21 s.c.; 0.15 i.p. (Mebs, 1972). LD50 of b-BuTX in mice (mg/g): 0.019 i.p. (Kondo).
Toxicity data: LD50 in mice (mg/g): 0.16 s.c. (Chang, Lee); also reported as 0.33 s.c. (Mebs, 1972); LD50 of a-Bgt in mice (mg/g): 0.21 s.c.; 0.15 i.p. (Mebs, 1972); LD50 of b-BuTX in mice (mg/g): 0.019 i.p. (Kondo)
Use: As exptl tools in investigating neuromuscular processes.

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