Lack of C5 Convertase-Generating Activity in Naja haje Cobra Factor

Abstract Commercial cobra factor is prepared from the venom of either Naja naja, the Indian cobra, or Naja haje, the Egyptian cobra, and is not marked as to source. Cobra factor from Naja haje (CVFh), although able to generate C3-cleaving activity, does not support passive lysis. Cobra venom from Naja naja (CVFn), upon incubation with normal human serum, depletes C3 through C9, and causes conversion of C3 and B as observed in immunoelectrophoresis. CVFh also causes conversion of C3 and B and depletes C3; but C5 through C9 are spared. CVFh and CVFn were found to be equally resistant to C3bINAhu. When CVFn was incubated with normal human or guinea pig serum, an activity was generated which was detectable as a zone of hemolysis in agarose plates containing guinea pig erythrocytes and EDTA, when placed near a well containing human or rat, but not guinea pig, CEDTA. Experiments with partially purified components showed that this activity corresponded to the CVFn-Bb complex, in that it could be generated from B, D, CVFn and Mg++ and required all of these. CVFh did not generate such an activity, showing that CVFh-B, if formed, is not a C5 convertase. Incubation mixtures of factors, B, D, and CVF destroyed C5hu and generated C56 from C5hu + C6hu only if formed from CVFn and not if formed from CVFh, whether or not additional C3 was present.