Inhibition of the enzymatic activity of the first component of complement (C1) by heparin

Abstract Classical enzyme kinetic analyses were applied to define the mechanism of the effect of heparin on the cleavage of the fourth (C4) and second (C2) components of complement by the first component (C1) of complement. The data indicated that heparin was a noncompetitive inhibitor of both C4 and C2 cleavage; cleavage of C2 was more sensitive to the action of heparin than cleavage of C4. Heparin blocked the action of C 1 in serum and three preparations of purified C 1 , each isolated by different methods. Heparin also inhibited the increased vascular permeability produced in normal skin by activated C 1 , suggesting that it or other polyions might be effective in the treatment of hereditary angioneurotic edema attacks.