Snake Venoms. The Amino Acid Sequences of TwoMelanoleuca-Type Toxins

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Abstract
Toxins CM-10 from Naja nivea and CM-9a from N. naja kaouthia venoms were purified by gel filtration followed by ion-exchange chromatography. Whereas toxin CM-10 contains 65 amino acids, toxin CM-9a contains only 64, but each includes 10 half-cystine residues. The complete primary structures of the toxins were established. The sequences and the invariant amino acids of toxins CM-10 from N. nivea and CM-9a from N. n. kaouthia venoms resemble those of the Melanoleuca-type toxins. In the 2 toxins the 10 structurally invariant amino acids of the neurotoxins and cytotoxins are conserved, but toxin CM-10 contains only 1 of the 3 functionally invariant amino acids of the neurotoxins, while toxin CM-9a contains none. As 8 of the 10 Cys residues of the Melanoleuca-type toxins are in similar locations to those of the neurotoxins and the cytotoxins of known structure, the residues from the 2 toxins investigated are presumed to link similarly. The remaining 2 Cys residues link differently.