Studies on the Nature of the Circulating Anticoagulant Directed against Antihemophilic Factor: With Notes on an Assay for Antihemophilic Factor

Abstract

Modification of the kaolin clotting time has produced a reliable, simple assay system for antihemophilic factor. This system has been utilized for an investigation of the nature and mode of action of the circulating anticoagulant directed against antihemophilic factor. The anticoagulant has been shown to be present in equal amounts in plasma and serum, to be associated with fractions II and III of plasma prepared by the method of Cohn, to be relatively heat stable and to be stable for prolonged periods at -20 C. Investigation of the kinetics of the anticoagulant-antihemophilic reaction has demonstrated its temperature, time, pH, and substrate concentration dependency. The anticoagulant is not inactivated during the reaction with antihemophilic factor, and there is a proportional relationship between the anticoagulant and the antihemophilic factor during their interaction. No antigen-antibody manifestations could be detected during the anticoagulant-antihemophilic factor reaction. These characteristics support the hypothesis that the inactivation of antihemophilic factor by specific circulating anticoagulants is enzymatic.