[Interaction of fibrinogen and fibrin with protamine sulfate].

Fibrinogen and fibrin sedimentation by different protamine sulphate preparations have been studied. Ionic strength and protamine sulphate concentration are found to influence the sedimentation reaction (paracoagulation). High sedimentation activity is inherent in protamine sulphate preparations with the lower electrophoretic mobility, that is with the higher molecular weight.

[Antithrombin III. Functional role and methods of determination (review)].

Antithrombin III (AT III) is the most important inhibitor of thrombin and other serine proteinases in the system of blood coagulation. AT III not only removes the excess of thrombin from blood but it inhibits the enzyme synthesis. AT III became functionally active in presence of heparin, which operates as a catalyst and accelerates significantly the formation of inactive complexes between AT III and proteinases, which usually developed slowly in absence of the activator.

[The role of complementary E2 and D2 centers in the reaction between fibrin and fibrinogen].

The effect of fibrinogen on the two steps of polymerization of two fibrin forms differing in the set of polymerization sites (fibrin-desAA and fibrin-desAABB) was studied. It was shown that fibrinogen inhibited the protofibril growth and fibril formation at the stage of lateral aggregation more effectively with fibrin-desAABB than with fibrin desAA. When the fibrinogen D2-site was blocked by tetrapeptide Gly-His-Arg-Pro, the key structure of the E2-site, the inhibitory activity of fibrinogen diminished.

[Interaction of an analog of the E1 site of tetrapeptide Gly-Pro-Arg-Pro with the D1 site of two forms of monomeric fibrin].

Two monomeric fibrin forms differing in a set of polymerization sites (fibrin desAA and fibrin-desAABB) are inhibited to a different extent by tetrapeptide Gly-Pro-Arg-Pro which simulates a moiety of polymerization site E1. The lesser sensitivity of fibrin-desAABB polymerization to the inhibiting tetrapeptide is due to the presence of active site E2 in it. A shape of the concentration dependence curve of the inhibitory effect of tetrapeptide Gly-Pro-Arg-Pro on the polymerization of both fibrin types is similar to the previously found curve for fibrinogen and its fragments--specific inhibitors of polymerization.