Staphylococcal Coagulase: the Nature of Plasma Activator in the Clotting Process

Abstract

IN 1944, Smith and Hale¹ showed that the clotting of fibrinogen by coagulase depends on an activator present in the plasma of certain animals, notably humans and rabbits. Since a fibrinogen–prothrombin complex prepared from human plasma by Mellanby's² acid precipitation method, which could be clotted by tissue kinase, could not be clotted by coagulase, they concluded that the activator was not prothrombin. Later, Tager³ and Tager and Hales⁴ noted certain resemblances between the physical properties of activator and prothrombin, both being precipitated with the globulin fractions in the region of pH 5.0 and by 50 per cent saturation with ammonium sulphate. In ethanol-precipitated fractions of plasma prepared by the method of Cohn⁵, activator was present in fractions III-1, III-2 and IV-1, whereas prothrombin is believed to occur only in III-2. Both prothrombin and activator were absorbed from plasma by barium sulphate; but considerable dissociation followed repeated Seitz filtration of human plasma, prothrombin activity being lost without comparable loss of activator. Studies by Kaplan and Spink⁶ disagreed with these findings, inasmuch as they found activator to be associated with the albumin fraction in ammonium sulphate fractionation, and to lie mainly in IV-4 of the ethanol precipitate.