Isolation and study of murine C3.

C3 was isolated in purified form from fresh murine serum and plasma by precipitation as euglobulin followed by removal of other proteins on immunoadsorbent columns bearing antibodies raised against specifically C3 depleted serum. Recovery was 30--55% and the C3 was all in its native form. Functional activity was demonstrated by fixation of the C3 on EAC142gp cells and by interaction with lymphocyte C3 receptors. Mouse C3 in plasma and after isolation had a molecular weight of 240,000. Its cleavage by classical pathway and cobra factor induced C3 convertases and by trypsin yielded a major conversion product with molecular weight not less than 210,000, the electrophoretic mobility of which differed when it was generated from isolated C3 rather than in plasma.