Estimation of the Third Component (C'3) of Complement. ∗

Abstract

The third component of complement (C'3) has been defined in terms of its role in a hemolytic system. It is also known as the component which is inactivated by cobra venom or by yeast. In an attempt to discover which fraction of yeast inactivated C'3, Pillemer and Ecker 1 succeeded in isolating an insoluble carbohydrate from yeast which destroys or removes the activity of C'3 in amounts vastly smaller than the whole yeast or the zymin preparation of Whitehead, Gordon and Wormall. 2 For the sake of simplicity this insoluble carbohydrate will henceforth be called zymosan † It was suggested that the inactivation of complement by yeast was due to the adsorption of C'3 on this carbohydrate. In a subsequent paper Ecker, Jones and Kuehn 3 noted that in the presence of 10% NaCl zymin did not inactivate C'3. Likewise, it has since been found that 10% NaCl suppresses the adsorption of C'3 by zymosan.

In the light of these facts it was therefor proposed to study the adsorbate with regard to the uptake of nitrogen. A stock suspension of the zymosan was made by placing it in saline (0.9%) in the proportion of 1 mg per ml. This lot of carbohydrate contained 3.14% N. Five ml of this zymosan suspension was added to each of a series of tubes, centrifugalized, and the supernates discarded. Varying amounts of pooled guinea pig serum were then added (in duplicate) to tubes containing the zymosan. Making use of the fact that the zymosan did not inactivate C'3 in the presence of 10% NaCl, duplicate tubes containing enough solid NaCl to make 10% were run parallel to each given quantity of serum.