Differentiation of Plasma Antithrombin Activities.

Abstract

The antithrombin capacity of plasma can be differentiated into 4 main effects. Antithrombin I is the adsorption of thrombin on fibrin. Antithrombin II is the co-factor of heparin. Antithrombin III neutralizes thrombin activity even in the absence of heparin, while antithrombin IV destroys thrombin only while it is being formed from prothrombin. Some of the properties of antithrombins II, III, and IV were investigated, together with those of the factor which acts with heparin to inhibit the activation of prothrombin, and which is referred to as the ''39 factor. The 4 activities have the common property of resistance to heating at 60[degree]C for 3 min., but are destroyed by heating at 70[degree]C. They are not adsorbed on BaCC3. They are water soluble. None of these activities is found in a commercial crystalized bovine plasma albumin. Antithrombin III activity is the only one removed by ether treatment of plasma. In ammonium sulfate fractionation antithrombin II is found predominantly in the 50-70% fraction, while antithrombin III is found only in the 0-50% fraction. It is believed that these 2 factors are two distinct entities. The relation of antithrombin IV to these 2 is not yet clear. It is possible that the ''39 factor and antithrombin I1 are identical.