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Toxicon. 1991;29(11):1315-27.

Lethal toxins and cross-neutralization of venoms from the African water cobras, Boulengerina annulata annulata and Boulengerina christyi.

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  • 1Pathophysiology Division, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011.


Venoms of the water cobras, Boulengerina, were assayed for lethality, proteolytic activity and protein content. Boulengerina annulata annulata and B. christyi venoms averaged 89% protein and lacked proteolytic activity. The murine i.p. LD50 of B. a. annulata and B. christyi venoms were 0.143 and 0.120 mg/kg, respectively. Polyvalent antivenom produced by the South African Institute of Medical Research neutralized 575 and 200 LD50 of B. a. annulata and B. christyi venoms/ml antivenom, respectively. Cation exchange chromatography resolved four lethal peaks from B. a. annulata venom and six lethal peaks from B. christyi venom. The major lethal peaks (about 12% of total venom protein) were purified further with molecular sieve chromatography and were characterized as 61 (B. a. annulata toxin) and 62 (B. christyi toxin) residue polypeptides with four half-cystines. Elucidation of the complete amino acid sequences indicated that these toxins belonged to the short-chain class of postsynaptic neurotoxins. Short-chain neurotoxins 1 from B. a. annulata and B. christyi had murine i.p. LD50 of 0.052 and 0.083 mg/kg, respectively, and showed over 80% homology with N. nigricollis alpha toxin. Reverse-phase analysis of another peak present in both venoms resolved a toxin that had an N-terminus identical to B. christyi short-chain neurotoxin 1. These fractions also contained toxins readily separable from the short-chain isotoxin by preparative reverse-phase chromatography. Amino acid sequencing of the first 28 residues indicated that both toxins were long-chain neurotoxins with identical N-termini. The LD50 of long-chain neurotoxins 2 from B. a. annulata and B. christyi venoms were 0.086 and 0.090 mg/kg, respectively. The venoms of these little-known elapids have the lowest LD50 of any African proteroglyph studied thus far and have high concentrations of potent postsynaptic neurotoxins.

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