Many types of venom contain components that activate complement. A major component of cobra venom is CVF which binds to the victim's factor B and this is then activated by factor D forming CVF,Bb. CVF, Bb is a serine protease specific for the victim's C3 and often C5 as well. The activity of this C3/C5 convertase is not affected by the complement regulatory proteins in blood and the complex is extremely stable (half-life approximately 7 hours).