VENOM COAGGLUTININ (VCA). THE PLATELET AGGREGATING PRINCIPLE OF BOTHROPS VENOMS: VON WILLEBRAND FACTOR-DEPENDENT PLATELET AGGREGATION

A review of the literature on snake venoms as they relate to blood coagulation and platelet aggregation is presented. A new snake venom fraction, venom coagglutinin (VCA), is introduced which aggregates animal platelets as well as those of man but only in the presence of von Willebrand factor (vWF). A survey of venoms for the presence of this fraction indicated it to be found mainly in the Bothrops venoms. A partial purification by chromatography was performed. VCA/vWF-induced aggregation was compared to that of ristocetin. Ristocetin-induced platelet aggregation was found to be limited to the aggregation of human platelets with human plasma and only a few animal plasmas. VCA caused aggregation of human and animal platelets with plasmas of both man and animal. The specificity of VCA as a vWF-dependent aggregator was evidenced by the ability of antibodies against vWF to inhibit VCA-induced aggregation.;VCA was partially characterized. Chromatography on a DEAE-cellulose column produced a highly active platelet-aggregating fraction. This fraction, with the procoagulant material removed, was stable at room temperature, heat labile and non-dialyzable. VCA has a molecular weight of approximately 29,000 as determined by polyacrylamide gel electrophoresis (PAGE) and stained for protein but not for carbohydrate. Treatment of VCA with trypsin caused loss of aggregating activity, further evidence that VCA is a protein. Disulfide reduction of VCA did not change its molecular weight on PAGE, but did result in a 75% loss of aggregating activity. VCA displayed no protease activity on casein and limited protease activity on N (alpha)-p-Tosyl-1-arginine methyl ester (TAME). Protease inhibitors and sulfhydryl inhibitors failed to interfere with VCA platelet aggregating ability. Weak fibrinolytic activity was present in the partially purified VCA, but was not related to the VCA platelet aggregating activity.;Quantitative bioassays of human and animal plasma vWF were made with VCA using both human and animal platelets. Aggregometric studies with human plasma, lyophilized animal platelets and VCA demonstrated the possibility of using animal platelets for human plasma vWF testing. Aggregation of animal platelet-rich plasma with VCA evidenced the importance of VCA as a probe for the study of plasma vWF.