An improved method for the isolation from Naja naja venom of cobra factor (CoF) free of phospholipase A

An improved method is reported for the isolation from cobra (Naja naja) venom of cobra factor (CoF), the anticomplementary protein which is derived from cobra C3. Sequential chromatography on DEAE-Sepharose, Sephacryl-S200, and finally hydroxylapatite yielded 6.25 mg CoF per gram of crude venom. The purified CoF had 1 unit of functional anticomplementary activity per 1--2 micrograms of protein, and was homogeneous on gradient and non-reduced sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis (PAGE). In SDS-PAGE after reduction with mercaptoethanol there were two major bands (M.W. 75,000 and 51,000 daltons), three minor bands (M.W. 29--31,500 daltons) and two trace bands (36,500 and 41,500 daltons). By analogy with mammalian C3 it is suggested that the CoF consists of two polypeptide chains linked by disulphide bridges, one of which undergoes cleavage of the peptide chain at several points either in vivo or in vitro.