The Preparation and Physicochemical Characterization of the Serum Protein Components of Complement

1. Methods for the separation from guinea pig serum in highly purified form of three of the components of complement are described. These substances are the so called mid-piece, end-piece, and 4th component. 2. Mid-piece has been separated as a euglobulin, with an electrophoretic mobility of 2.9 x 10(-5) in phosphate buffer of ionic strength 0.2 at pH 7.7, and with a sedimentation constant of 6.4 x 10(-13) in potassium chloride of ionic strength 0.2. 3. End-piece and 4th component were found together in a euglobulin fraction of serum which contained 10.3 per cent carbohydrate and had an electrophoretic mobility of 4.2 x 10(-5) in phosphate buffer of ionic strength 0.2 at pH 7.7.