[Estimating ability of dihydroquercetin to inhibit oxidation of fibrinogen by ozone].

The ability of dihydroquercetin to inhibit the oxidation of fibrinogen has been evaluated. It is established that dihydroquercetin inhibits oxidation of fibrinogen by ozone, thus preventing oxidative modification of fibrinogen and preserving its functional activity.

[Interaction of fibrinogen with magnetite nanoparticles].

The interaction between fibrinogen and magnetite nanoparticles in solution has been studied by the methods of spin labeling, ferromagnetic resonance, dynamic and Rayleigh light scattering. It was shown that protein molecules adsorb on the surface of nanoparticles to form multilayer protein covers. The number of molecules adsorbed on one nanoparticle amounts to approximately 65 and the thickness of the adsorption layer amounts to approximately 27 nm. Separate nanoparticles with fibrinogen covers (clusters) form aggregates due to interactions of the end D-domains of fibrinogen. Under the influence of direct magnetic field, nanoparticles with adsorbed proteins form linear aggregates parallel to force lines. It was shown that the rate of protein coagulation during the formation of fibrin gel under the action of thrombin on fibrinogen decreases approximately 2 times in the presence of magnetite nanoparticles, and the magnitude of the average fiber mass-length ratio grows.

[Mechanism of enzymatic crosslinking of fibrinogen molecules].

The mechanism of enzymatic covalent crosslinking of fibrinogen molecules under the effect of plasma transglutaminase (factor XIIIa) has been studied. Using the methods of elastic and dynamic light scattering combined with viscosimetry and electrophoresis of the reduced samples, it has been shown that fibrinogen oxidation strongly accelerates self-assembly of the covalently cross-linked fibrinogen polymers. IR-spectroscopy data indicate that the degree of fibrinogen oxidation positively correlates with the amount of epsilon/gamma(-glu)lys isopeptide covalent bonds whose formation is catalyzed by the factor XIIIa. The results of this and our previous studies cast doubt on the widespread concept that native fibrinogen is the substrate for factor XIIIa. In our opinion, only structurally defective fibrinogen molecules that have undergone oxidative structural conversion in the D-domain region are involved in the enzymatic reaction leading to the formation of covalent epsilon/gamma(-glu)lys isopeptide bonds and self-assembly of fibrinogen polymers.

[The effect of "aging" of fibrinogen molecule on the structure and properties of fibrin gel].

The effect of molecular "aging" of fibrinogen stimulated by preincubation in solution on the fibrin three-dimensional architecture, its ability to crosslink fibrin-stabilizing factor, and the sensitivity of fibrin gel to plasmin hydrolysis have been studied. The method of elastic light scattering was used to demonstrate that fibrin generated from "defective" fibrinogen had a coarser structure with a higher mean mass-length ratio of polymeric fibers compared to native fibrinogen (2.24 x 10(9) and 1.46 x 10(9) g/(mol x cm), respectively). Crosslinking had no effect on the architecture of both control and experimental fibrin samples. Spectrophotometric and electrophoretic analysis has shown a higher sensitivity of coarse fibrin gels to plasmin. A close correlation between spontaneous local conformational reconstructions in fibrinogen molecule and its functional activity is concluded.

[Protein inhibitors of fibrin stabilizing factor FXIII].

The ability of cysteine proteinase inhibitors (CPIs) isolated from tubers of potato (Solanum tuberosum) to suppress transpeptidase activity of fibrin stabilizing factor (FXIIIa) through the direct effect on the essential SH group of the enzyme active site has been studied. The formation of fibrin clots soluble in 5 M urea and 2% acetic acid as well as spectrophotometric turbidity analysis of the stabilization and resistance of fibrin clots formed in the presence of FXIIIa and CPIs from potato tubers to plasmin, and electrophoresis of reduced fibrin samples indicate the decrease or absence of covalent crosslinking of fibrin chains. In addition, CPIs added to the substrate proved to decelerate fibrinogen polymerization almost twice relative to control. It is concluded that natural CPIs can both take part in the regulation of FXIIIa transpeptidase activity in vitro and modify the substrate.

[Polymeric systems with antithrombin activity for thermally activated targeting]. / Polimernye sistemy s antitrombinovoi aktivnost'iu dlia termoaktiviruemogo napravlennogo transporta.

Copolymers of N,N-diethylacrylamide and N-acryloylphthalimide with lower critical solution temperature (LCST) were synthesized by radical copolymerization. Polymeric systems with antithrombin activity and LCST were prepared via a reaction of amino groups of hirudin with phthalimide groups of the copolymers. On increasing hirudin content, LCST of the polymeric systems increased. The antithrombin activity of polymeric systems obtained by hirudin immobilization on copolymer carriers was inversely related to the content of the copolymer, amounting to 6% of the activity of native hirudin.

[Influence of end products of plasmin-mediated hydrolysis of fibrinogen and fibrin (EF and Ef fragments) on fibrinogen cross-linking]. / Vliianie konechnykh produktov plazminovogo gidroliza fibrinogena i fibrina--fragmentov EF i Ef na protsess perekrestnogo sshivaniia fibrinogena.

We studied the influence of the end products of plasmin-mediated hydrolysis of fibrinogen and nonstabilized fibrin (EF and Ef fragments) on covalent cross-linking of fibrinogen molecules catalyzed by a fibrin-stabilizing factor (factor XIIIa). The data on elastic and dynamic light scattering reveal no difference in the spatial structure of covalently linked fibrinogen molecules in the presence of the hydrolysis end products EF and Ef. In contrast to the inactive fragment EF, fragment Ef significantly accelerates the enzymatic reaction. This is also confirmed by electrophoresis of the reduced samples indicating a relatively fast accumulation of gamma-dimers and A alpha-polymers as compared to the control samples. Possible molecular mechanisms of this effect are discussed.

[Mechanism of cross-linking of fibrinogen and its early structural homolog fragment X]. / Mekhanizm perekrestnogo sshivaniia fibrinogena i ego rannego strukturnogo gomologa X-fragmenta.

We studied the mechanism of the cross-linking of fibrinogen as well as its closest structural homolog X fragment under the influence of a fibronectin-stabilizing factor (factor XIIIa). The data on elastic and dynamic light scattering indicate the formation of single-stranded polymers without any structural rigidity that acquire a ramified and compact structure upon reaching critical mass. The values of coefficients of translational diffusion, mean-mass molecular weight, averaged scattering factor, and the accumulation of gamma-dimers indicate that preincubation of fibrinogen and fragment X solutions significantly accelerates the enzymatic formation of a covalently bound macromolecular protein complex. We propose that enzymatic cross-linking proceeds only with the gradual accumulation of structurally imperfect molecules of fibrinogen and fragment X that are prone to intermolecular D-D end-to-end contacts.

[The structural transformations of X-oligomers]. / Strukturnye prevrashcheniia X-oligomerov.

Mechanism of self-assembly and the three-dimensional organization of the intermediate soluble forms of X-oligomers in the presence of non-denaturing urea concentration have been studied by dynamic light scattering, analytical ultracentrifugation, and viscometric methods. Swedberg and Kuhn-Mark-Hauwink analysis of the obtained hydrodynamic data accounting the concentration effect on translational friction demonstrated formation of equilibrium single-stranded rod-like protofibrils with end-to-end arrangement of the peripheral domains of X monomers. Upon elongation the single-stranded protofibrils form double-stranded structures through lateral aggregation. We infer that alpha C domains are involved in neither stabilization of the single-stranded structures nor their dimerization.

[The role of DL and DH degradation products in the reactions of the plasmin hydrolysis of fibrinogen and fibrin]. / Rol' produktov degradatsii DL i DH v reaktsiiakh plazminovogo gidroliza fibrinogena i fibrina.

The mechanism of effect of plasmin hydrolysis degradation products, fragments DL and DH, on fibrinolysis and fibrinogenolysis processes was investigated on the basis of their various structural and functional characteristics. Using electrophoresis of unreduced samples and degradation products concentrations changing kinetics, DH was shown to be the only fragment which possessed an antifibrinolytic effect. Rauleigh's light scattering analysis indicated the ability of fragments DL and DH to co-form with plasminogen reversible equimolar complexes.

Mechanism of aggregation of fibrinogen molecules: the influence of fibrin-stabilising factor.

The physicochemical mechanism of aggregation of fibrinogen has been investigated in the presence and absence of fibrin-stabilising factor (factor XIIIa). Data from elastic and inelastic light-scattering and viscometry show that molecules of fibrinogen undergo a spontaneous modification of their carboxyl terminals and bind 'end to end' into flexible polymer chains. On attaining a critical length, the single-filament polymers twist into a coil and aggregate to form branched molecules in which the segments are packed sufficiently densely to resemble strongly hydrated globular particles. The formation, under the influence of factor XIIIa, of epsilon/gamma-glutamyl-lysine covalent bonds produces only insignificant changes in the spatial organisation of the fibrinogen aggregates. Covalent dimerisation of the gamma-chains restricts the structural flexibility of the polymers, but linking of the alpha-chains provides progressive compaction of the structure with increase in molecular weight. Electrophoresis of reconstituted samples shows that the coil-shaped chains of fibrinogen oligomers prevent the complete enzymatic linking of the gamma-chains. The results of this work suggest that the accelerated assembly of multimolecular aggregates, seen in the presence of factor XIIIa, may be explained by the stabilisation of intermediate complexes of fibrinogen, which makes the spontaneous transition from a stable native state to the activated state irreversible.

[The effect of fragment D on the aggregation of fibrinogen molecules in solution]. / Vliianie fragmenta D na agregatsiiu molekul fibrinogena v rastvore.

The mechanism of fibrinogen aggregation in the presence of fragment D has been studied. The values of translational diffusion coefficients, specific viscosity, average molecular masses, and Zimm factor of light scattering indicate that fragment D accelerated assembly of fibrinogen molecules that form flexible polymeric chains with tail-to-tail association due to spontaneous structural modification of COOH-terminal regions. Electrophoresis did not reveal the presence of fragment D in polymer fraction of non-reduced samples. The data obtained allowed to conclude that at initial stages fragment D forms unstable complexes with structurally modified fibrinogen molecules. These complexes serve as intermediates in the multistep process of assembly of supermolecular protein complex.

[The antifibrinolytic action of the D-dimer fragment]. / Antifibrinoliticheskoe deistvie fragmenta D-dimera.

The effect of D-dimer on the process of plasmin hydrolysis of unstabilized and crosslinked fibrin has been studied. Less degraded early, intermediate, and late products of fibrin cleavage have been revealed by electrophoresis of reduced and nonreduced samples. The molecular mechanism of antifibrinolytic effect of the D-dimer is supposed to be determined by shielding of peptide regions of monomer fibrin, localized both in N-terminal area of beta chain and in alpha, beta, and gamma chains between D and E domains. A notion has been proposed of autoinhibition of fibrinolytic reaction as a phenomenon related to the physical-chemical regulation of fibrinogen transformation into fibrin.

[Multidomain structure of fibrinogen and its transformations]. / Mul'tidomennaia struktura fibrinogena i ego prevrashcheniia.

Generalized concepts of some structural peculiarities of fibrinogen, its transformation into fibrin and assembly have been considered on the basis of author's and published data. The role of local conformational changes in different areas of fibrinogen molecule and of separate reaction centers in formation of single- and double-stranded rod-like equilibrium fibrin oligomers and flexible branched copolymers of fibrinogen with fibrin E fragment has been considered. The mechanism of compactization has been discussed.