Cholinesterase inactivation by snake venoms

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Abstract
Cholinesterase-inactivating activity (anticholinesterase) of the Formosan cobra venom (Naja venom) is reversibly inhibited by various cations. Mg is by far the most potent ion tested; Na and K are least active in this respect. Other activators or stabilizers of cholinesterase, such as cysteine, reduced glutathione, citrate, HCN, gelatin, albumin and gum acacia, are also inhibitors of the Naja-venom anticholinesterase. The inactivation of cholinesterase by the Naja-venom anticholinesterase is irreversible, since once the cholinesterase has been inactivated by the anticholinesterase, none of the anticholinesterase inhibitors can restore the activity. In addition to the inhibition of the Naja anticholinesterase, most of the inhibitors increase the cholinesterase activity beyond its original value. The possible cause is discussed. The optimum pH range for the Naja-venom anticholinesterase is between 6.0 and 8.5. It loses its activity completely below 5.0 or above 10. The Naja-venom anticholinesterase is completely destroyed by heating at 60[degree] for 10 min. Its activity disappears for the most part after dialysis of a 0.2[degree]/o solution. The anticholinesterase activity of Naja venom seems not to be due to a proteolytic enzyme, since no parallelism between the 2 types of activity of various snake venoms could be found. The Naja-venom anticholinesterase does not affect the cholinesterase preparations of various tissues of the rabbit such as erythrocyte, serum, heart muscle and brain, since they apparently contain some factors which inhibit the anticholinesterase completely. These factors are heat-resistant (100[degree], 10 min) and at least partially dialyzable.