IDENTIFICATION OF A THROMBOPLASTIN INHIBITOR IN SERUM AND IN PLASMA 1

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Abstract
A clotting system is descr. consisting of easily prepd. stable clotting components which is sensitive to tissue thromboplastin. Incubation of known quantities of purified human thromboplastin with human serum or plasma (barium sulfate-adsorbed) results in a progressive loss of thromboplastic activity as measured by this clotting system. Potent thromboplastin prepns. are almost completely inactivated in this manner. The inactivating factor has been identified as a thromboplastin inhibitor which requires Ca for its action. Its effect can be easily reversed by temporary removal of the calcium. The inhibitor is heat labile at 56[degree]C and can be separated from adsorbed serum by ammonium sulfate fractiona-tion between the levels of 40 and 50% saturation. It is water-soluble, non-dialyzable and appears to be fairly stable in serum. It does not appear to be analogous to the lipid inhibitors descr. by others. The reversal of the effect of this inhibitor by removal of calcium appears to offer an explanation for the reported coagulant effect of reduction in calcium concn. The inhibitor may play a significant role in maintaining the normal fluidity of blood in vivo.