title: Formation and function of a complex of the C3 proactivator with a protein from cobra venom.
abstract: The role of C3 proactivator (C3PA) and a factor isolated from cobra venom (CoF) in the formation of a principle able to cleave C3 was investigated. The results clearly demonstrate two modes of interaction of C3PA with CoF. In isolated form, C3PA and CoF were found to form a reversible protein-protein complex in free solution. This complex had some C3 cleaving activity. In the presence of minute amounts of a partially purified normal serum substance, factor D, the C3PA-CoF complex was stabilized and its efficiency in cleaving C3 was greatly increased. Factor D is thus an activator of C3PA. A firm complex composed of C3PA and CoF, and possessing C3 cleaving activity, was also formed by addition of CoF to serum.
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D003165:Complement System Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007456:Iodine Isotopes; D010587:Phagocytosis; D012911:Snakes; D014688:Venoms
chemical_list: D007456:Iodine Isotopes; D014688:Venoms; D003165:Complement System Proteins