Crystalline phospholipase A associated with a cobra venom toxin.

Abstract

COBRA venom has been used as a source of phospholipase A activity1–3, and Braganca and Sambray showed that there are multiple forms of phospholipase A in cobra venom4. In the course of a study of the toxic components of the venom of the Indian cobra, Naja naja, we discovered that a very potent central nervous system toxin (corticotoxin I) is associated with a high phospholipase A activity. This component was isolated by ammonium sulphate fractionation and chromatography on carboxymethyl ‘Sephadex G-25’ and finally crystallized. A photograph of the crystalline product is shown in Fig. 1. The specific phospholipase activity of the crystals, assayed in ether suspension by a modification of the technique described by Long and Penny5, was 150 U/mg. (A phospholipase unit is the amount of activity which results in the liberation of 1 µmole of fatty acid per min at 20° C.) There was no detectable myoneural toxic activity, as determined by the procedure described by Vick et al.6, using anaesthetized dogs. The crystals can be separated into two major components either by electrophoresis on cellulose acetate strips or by chromatography on DEAE cellulose. The specific phospholipase activity of both components was similar in the conditions of our assay. The amino-acid composition of the acid hydrolysates of the two components was nearly identical, as shown in Table 1. Amide content has not been determined so far, and there may be a difference in the number of free carboxyl groups. Work is now in progress to compare the substrate specificities, kinetic parameters and physicochemical properties of the two components.