ON THE INACTIVATION OF THROMBIN BY PLASMA PROTEIN

Abstract

A study is made in vitro of the inactivation of thrombin by constituents of the plasma. In the clotting of fibrinogen by thrombin, inactivation of the residual thrombin does not occur; in the clotting of plasma, however, the excess thrombin is rapidly inactivated, and the reaction proceeds exponentially. Serum also contains the inactivating agent, and by testing different serum protein fractions, maximal inactivating power resides in the albumin fraction soluble at 2.60 M. but precipitated at 2.80 M. (NH4)2SO4. The inactivation phenomenon is probably enzymatic in nature and is an essential feature of normal blood clotting. The possible relationship to vit. K is discussed.