The basic proteins of cobra venom. I. Isolation and characterization of cobramines A and B.

Cobra venoms contain heat stable, basic, proteins that inhibit iodide accumulation by thyroid slices. Activity is not related to the content of phospholipase A or various other enzymatic activities. These proteins are present only in Elapid venoms and not in snakes of the Crotalidae or Viperidae families. Two such basic proteins, named cobramines A and B, have been purified from the crude venom of the Indian cobra (Naja naja) by carboxymethyl cellulose chromatography, gel filtration, and ammonium sulfate crystallization. Together they constitute -40% of the venom protein. Their isoelectric points are N11.9 and -12.6, respectively. Cobramine B was found to be homogeneous in paper and disc gel electrophoresis and by ultracentrifugation (s~~,~ = 0.98). The molecular weight was 6400 from equilibrium centrifugation measurements and 5840 on the basis of amino acid analysis (52 residues).