Characterization of a form of bovine factor VIII which does not aggregate human platelets

Fractionation of partially purified bovine factor VIII on tricalcium citrate columns produces a material which contains high levels of factor VIII procoagulant activity and factor VIII-related antigen, but does not aggregate human platelets. The procoagulant activity can be blocked by human inhibitors of factor VIII: C and by rabbit antibody to bovine factor VIII. Its activity can be increased by thrombin modification. The apparent molecular weight of this form of factor VIII is significantly lower than that of the forms of factor VIII which contain platelet aggregating activity, and it exhibits a higher mobility on agarose electrophoresis.