The Demonstration in Human Serum of “Conglutinogen-Activating Factor” and its Effect on the Third Component of Complement

Abstract

It has been found that the intermediate complex EAC′1a,4,2a,3, if built-up with purified complement components, fails to react with bovine conglutinin. The participation of a further serum factor, distinct from the hitherto described complement components, is required for the reactivity toward conglutinin to be acquired. To this factor the name conglutinogen-activating factor (or KAF) has been provisionally given. KAF has been partially purified from human serum and has been found to be a β-globulin with a molecular weight of approximately 100,000. It appears to be present in serum in very small quantities. KAF reacts specifically with bound C′3 and no other complement components are necessary for the reaction to occur. The nature of the reaction on bound C′3 is unclear, but it seems more likely that KAF produces some change, possibly enzymatically, in the bound C′3 molecule than that KAF is bound stoichiometrically on the alexinated complex. Besides activating the conglutinogen, KAF makes bound C′3 very much more sensitive to enzymatic attack.