Chain Structure of Cobra Venom Factor from Naja naja and Naja haje venom

The chain structure of cobra venom factor, whether isolated from Naja naja venom (CVFn) or from Naja haje venom (CVFh), is similar. Both homologous proteins are composed of three disulphide‐linked chains (A, B, and C) with apparent molecular weights of 72,000, 54,000, and 27,000–35,000 for CVFn and 68,000, 51,000, and 30,000–32,000 for CVFh. That all three polypeptides are integral parts of CVF was demonstrated by investigation of the chain pattern after partial reduction. Reduction with 1–2 mM dithiothreitol under nondenaturing conditions yielded free B‐chain, together with an intermediate product composed of disulphide‐linked A‐ and C‐chains. The C‐chain was heterogenous when investigated by electrophoresis in polyacrylamide slab gels in the presence of SDS. Similarly, isoelectric focusing of CVFn and CVFh showed a multiplicity of bands in the pH range 5.2–6.4. Limited tryptic digestion resulted primarily in the fragmentation of the B‐chain. CVFh is much more sensitive to tryptic attack than CVFn. In all our preparations of CVFh a partial, trypsin‐like fragmentation of the B‐chain was detectable to various extents.