Isolation of the Anticomplementary Protein from Cobra Venom and its Mode of Action on C3

Abstract

Cobra factor, a protein of the venom of Naja naja, was isolated. It was characterized as a glycoprotein with a molecular weight of 144,000 and an electrophoretic mobility of a β globulin at pH 8.6. Added to whole human serum it converted and inactivated C3. The effect on C3 was found to be dependent upon a non-complement plasma protein and on bivalent cations. To generate C3-directed enzymatic activity, cobra factor had to enter into a firm complex with the plasma protein, a 5S thermolabile β pseudoglobulin.