SODIUM IONS AS THE EFFECTOR OF CATALYTIC ACTION OF -THROMBIN
M. V. Kololdzeyskaya, G. L. Volkov
A process of thrombin interaction with synthetic and natural substrates in the presence of Na+ ions has been analyzed in the survey. Molecular bases of this interaction have been presented, interrelation between the structure and function of thrombin has been noted; the nature of the unique site of its active centre which determines high thrombin affinity for the substrates and increase of its catalytic activity defined by the term of “specificity to univalent cations” have been considered in detail. Na+ ions play the role of allosteric effector in realization of two informational states of thrombin which penform, respectively, two fundamental and competing functions in the process of hemostasis. The molecular basis of the process of Na+ binding with thrombin is rather simple and depends only on the single site which importance for the enzyme function is marked by numerous investigations of a number of authors, and it is shown that Na+-binding site is distributed in the other zone of thrombin molecule as compared to exosites I and II, which do not take part in Na+-binding and allosteric transduction. Considerable attention was given to conformational conversions of a thrombin molecule caused by Na+ ions binding. It was shown that the transition slow ? fast of the enzyme forms leads to formation of the ion pair Arg-187: Asp-222, optimal orientation of Asp-189 and Ser-195 for binding of substrates and considerable shift of the lateral chain Glu-192 determined by the disturbance of the lattice of water molecules which connects Na+-binding site with aminoacid Ser-195 of the active centre of the enzyme. New data have been presented which indicate that the changes in the lattice of water molecules and allosteric nucleus of Na+-binding site of the enzyme are the basic link of raising the affinity between the thrombin and substrate and mechanism of the enzyme activation by Na+-ions. The survey touches some problems of creation of allosteric inhibitors of thrombin which can take essential effect on Na+-binding site and favor stabilization of the anticoagulant slow-form of thrombin, and of enzyme rational mutants with selective specificity in respect of protein C which display effective and safe anticoagulant and antithrombotic effects in vivo.
Key words: thrombin, univalent cation specificity, Na+-binding site, thrombin activity modulations, allosteric molecule nucleus, anticoagulant activity, procoagulant activity, protein C.
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