ABSTRACT
Venoms from cobras and the African Ringhals snake contain several different kinds of toxic proteins. The most lethal are the α-neurotoxins, which are single-chain proteins of about 60 or 70 residues. These toxins bind to nicotinic acetylcholine receptors, and they cause death by paralyzing respiratory muscles. Cobra venoms also contain large quantities of other proteins that are similar in size to the neurotoxins, but do not bind to cholinoceptors. These proteins are toxic to mice, at intravenous median lethal dose values of about 1 µg/g body weight. Their toxicity is primarily associated with direct effects on the heart and, hence, they were named "cardiotoxins". Because cardiotoxins can have lytic effects on a wide range of cells, other names have been proposed for them: direct lytic factor, cytotoxin, cobramine, membrane-active polypeptide, membrane-disruptive polypeptide, membrane toxin, and membranotoxin. The cardiotoxin fraction had about 15 times the activity of the whole venom, and it was demonstrated to contain a basic protein.
