Isolation and characterization of granulocyte lysosomal proteins and study of their effects on the clotting system

Lysosomes (granules) of rabbit PMN leukocytes were extracted with either HCl or H2SO4, and the extracts were chromatographed over Sephadex to separate protein constituents. Some of the low molecular weight cationic proteins homogeneous on SDS PAGE (8% and 12.5% gels) were characterized by electrophoretic mobility in acid gels and by amino acid analysis. A 3,700 dalton polypeptide, rich in arginine and cysteine, prolonged the partial thromboplastin time of normal plasma. In low concentration, this protein shortened the clotting time of pure fibrinogen by thrombin. In high concentration this lysosomal cationic protein precipitated fibrinogen from solution; no fibrinopeptides were released to suggest cleavage of fibrinogen. Fibrinolytic protease activity was detected in crude H2SO4 extracts but not in crude HCl extracts. Two separate plasminogen activators, differing from kallikrein or prekallikrein, were isolated from the H2SO4 lysosomal extract and were partially characterized; neither exhibited proteolytic activity on fibrinogen free of plasminogen.