PLATELET EXTRACTS, FIBRIN FORMATION AND INTERACTION OF PURIFIED PROTHROMBIN AND THROMBOPLASTIN

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Abstract
With the use of purified clotting agents, it was shown that bovine platelet extracts contain an accelerator of prothrombin activation. They contain only a small amt. of thromboplastin. The accelerator is apparently present in platelets in the active form and acts similarly to serum Ac-globulin. The platelet accelerator is apparently a protein. It is destroyed by heating at 53 C, is non-dialyzable and is precipitated by half-saturation with ammonium sulfate. It is sharply distinguished from Ac-globulin by being mostly sedimented by centrifuga-tion at 32,000 g. Bovine platelets also contain a substance which hastens the 2d stage of clotting. This substance is non-dialyzable, stable to heat at 53 C for 30 min., precipitated by half-saturation with ammonium sulfate, and is not sedimentable by centrifugation at 32,000 g. Platelet extracts shorten considerably the clotting time of bovine plasma. It has been postulated that platelets aid in the initial formation of thrombin primarily by catalyzing the interaction of prothrombin and thromboplastin. This thrombin then activates the inert plasma Ac-globulin to its active counterpart, serum Ac-globulin, which acts as the principle accelerator of the 1st stage of clotting.