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

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Abstract
The chain structure of cobra venom factor, whether isolated from Naja naja venom (CVFn) or from Naja Haje (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 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 non-denaturing 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.