ABSTRACT
Cardiotoxin II of the Indian cobra (Naja naja) contains approximately four Mg2+ per mol. Complete demetallation of the toxin is achieved by three cycles of treatment with ethylenediamine tetraacetate and gel filtration. Reconstitution of toxin by treatment of the apo-protein with Mg2+ restores metal content and inorganic pyrophosphatase activity only to the extent of two atoms/mol and 65%, respectively. Use of Mg (II)-EDTA in the reconstitution experiment yields restoration of half the original enzyme activity. Mg2+ is required for the inorganic pyrophosphatase action of the toxin. A definitive statement on the non-essentiality of Mg2+ for the lethal toxicity of the toxin is not possible at present, although experimental observations indicate that demetallated toxin is as toxic as the native toxin. Based on this and the differing sensitivities of the enzyme and toxic activities of the toxin to heat, it is suggested that the reaction centres in the toxin for the two activities are different and that the pyrophosphatase activity is not causally connected with the lethal toxicity of the toxin.
ABSTRACT
An inorganic pyrophosphatase has been purified to apparent homogeniety from Indian cobra (Naja naja) venom, with a ten fold increase in specific activity. The enzyme activity is intrinsic to a protein fraction in the venom which is normally termed cardiotoxin, cobramine, cytotoxin and so on. The enzyme shows a low Km (70 μΜ) and high heat stability. The enzyme was active against sodium pyrophosphate; it also hydrolyses a few mononucletides and sugar phosphates at much lower rates. The physiological significance of inorganic pyro phosphatase in venom is discussed.