Rapid isolation of endogenous inhibitor of factor B

An inhibitor of mouse factor B was purified from lysate of L cells by a human factor B-affinity column. The purified inhibitor was found to be homogeneous with a molecular weight of about 25,000 and identical to the 25K protein isolated from L cell-lysate by the coprecipitation method with anti mouse factor B. Hemolytic titration of the activity and PAGE-analysis of the inhibitor-factor B complex showed that 1 mol of inhibitor reacted with 1 mol of mouse factor B and inactivated its hemolytic activity.