Effects of cobra neurotoxin on membrane properties of synaptosomes

Abstract

Investigations presented in this paper deal with effects of cobra venom neuro­toxin on functional and membrane properties of synaptosomes relating to its neurotoxic action. Cobra venom is a complex mixture of biologically active proteins, many of which are enzymes and these have been well characterised. The lethal action of this venom is brought about by two neurotoxic protein components. They are known to cause death by paralysis of the respiratory muscles. Numerous studies including those of Kellaway, Cherry and Williams, (1932) have demonstrated that cobra neurotoxin blocks neuromuscular trans­mission. A great deal is known about the protein structure of snake venom neurotoxins and some of these have been sequenced (Lee, 1972). The cobra (Naja naja) venom neurotoxin used in the experiments described here, is a low molecular weight (10,000) protein. It has seven disulphide linkages which probably explains its high solubility in water. It is very stable and can be heated to 100°C for 10 min at pH 5.0 without loss of activity. In addition to the neuro­toxins which are responsible for its lethal action, this venom contains several other cytotoxins. Among these may be included a whole family of isoenzymes having phospholipase A activity (Braganca and Sambray, 1967) which seem to differ in their ability to attack particular fatty acids in the phospholipids, and a cytotoxic protein which has no enzymic activity but is preferentially lytic to certain cells including some tumour cells.