[Antithrombin III. Functional role and methods of determination (review)]. / Antitrombin III. Funktsional'naia rol' i metody opredeleniia (obzor).

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. AT III and heparin cofactor are synonyms and designate the same substance. Modern procedures for estimation of AT III in blood plasma are reviewed.

[Inhibition of fibrin assembly by fragment D and its dimer derived from fibrinogen and stabilized fibrin. Evidence for the two-step type of inhibition]. / Tormozhenie sborki fibrina fragmentom D, poluchennym iz fibrinogena, i ego dimerom iz stabilizirovannogo fibrina. Podtverzhdenie dvukhfaznosti effekta tormozheniia.

The influence of purified fragments D and DD on fibrin monomer polymerization has been studied. When applied separately, DD is less strong an inhibitor than D. An addition of small amounts of DD to the reaction mixtures containing D does not change the inhibitory effect, when the concentration of the latter fragment is low. At high concentrations of D the contribution of DD becomes more pronounced. Small amounts of D added to DD-containing systems strongly enhances the inhibition. These properties of the D--DD mixtures are unpredictable and puzzling; they contradict the generally accepted view that the specific inhibitors of fibrin polymerization, to which D and DD belong, act in a simple competitive way. The whole incomprehensible situation may be clarified in terms of a hypothesis on a two-step mechanism of inhibition. It is assumed that at the first (preliminary) step of the inhibitor effect DD is less competent than D, whereas at the second step DD possessing a high affinity for the fibrin monomer, functions as the most effective competitive inhibitor.

[Isolation of the fragment D dimer from stabilized fibrin and a study of its antipolymerization action]. / Vydilennia dymeru frahmenta D zi stabilizovanoho fibrynu ta doslidzhennia ioho antypolimeryzatsiinoï diï

The dimer of fragment D is isolated preparatively by CM-cellulose chromatography (in neutral medium) from dialyzed tryptic hydrolyzate of stabilized fibrin. Contrary to the fragment D monomer obtained from fibrinogen under the same conditions, the dimer itself cannot inhibit polymerization of monomeric fibrin. However with the presence of monomer D in the amount sufficient for essential inhibition of the fibrin polymerization the addition of dimer D produces the further delay in polymerization. Under these conditions dimer D is highly effective inhibitor if its amount is not too little, as its small doses are not effective.

[New data on the structure of fibrinogen]. / Novye dannye otnositel'no struktury fibrinogena

The results of physical and chemical investigations show the closeness of fibrinogen to globular proteins, but some differences from globular proteins in certain characteristic features are found resulted from high asymmetry or high hydration of the molecule. The results of electron microscopy cannot be interpreted in a simple way, but nevertheless they show the presence of conformational mobility and existence of configurational isomers. The amino acid sequence of the most important parts of a fibrinogen molecule is known now: "the N-terminal disulphide knot" including peptides A and B being splitted by thrombin, and the part of the gamma-chain participating in covalent binding of fibrin. The study of plasmin and CNBr split products is a fruitful approach to the study of fibrinogen structure and the chemical models of fibrinogen are based on them. In the latest models the N-terminal parts of all 6 polypeptide chains of fibrinogen are located in the centre of a molecule, so the earlier concepts on monomeric fibrin polymerization in the end-to-end way must be reconsidered. None of the existing models produces a definite description of the functional properties of fibrinogen; the appearance of such a model is expected in the nearest future.