Factor VIII and human platelet aggregation. IV. Effect of proteolytic enzymes on platelet aggregation by factor VIII.

During digestion of highly purified bovine factor VIII or neuraminidase-treated human factor VIII by plasmin the procoagulant activity is destroyed more rapidly than the aggregating activity. At an intermediate stage, fragments are transiently formed, which inhibit platelet aggregation by the respective undigested materials, but without corssed inhibition. During proteolysis by plasmin, human factor VIII retains antigenic and restocetin cofactor properties. Contrary to previous observations obtained with less purified preparations, plasmin digest of human or bovine factor VIII do not inhibit ADP-induced platelet aggregation. Thrombin and reptilase do not modify the aggragating activities of bovine and neuraminidase-treated human factor VIII.