Snake venoms. The amino acid sequences of two Melanoleuca-type toxins

Toxins CM-10 from Naja nivea and CM-9a from Naja 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 they each include ten half-cystine residues. The complete primary structures of the toxins have been 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 two toxins the ten structurally invariant amino acids of the neurotoxins and cytotoxins are conserved, but toxin CM-10 contains only one of the three functionally invariant amino acids of the neurotoxins while toxin CM-9a contains none. As eight of the ten cysteine 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 two toxins investigated are presumed to link similarly. The remaining two cysteine residues link differently.