[Mechanism of self-assembly of soluble fibrin oligomers and the role of fibrinopeptides A and B in this process].

Three-dimensional organization of intermediate soluble forms of fibrin-polymers--a product of fibrin-monomer assembly--in the presence of non-denaturating urea concentrations has been studied. Hydrodynamic parameters of fibrinogen and fibrin-polymers were obtained by viscosimetry, dynamic light scattering and analytic ultracentrifugation. Using Yamakawa's hydrodynamic theory and considering fibrinogen molecule as an oblate ellipsoid of revolution made it possible to estimate the concentration effect on the coefficient of translational friction in the first, according to concentration, linear approximation. Hydrodynamic constants against polymer molecular weights were plotted using Swedberg's and Kuhn--Mark's equation. This made it possible to prove the existence of equilibrium single-stranded protofibrils formed by fibrin-monomer "end-to-end" association. It was concluded that local conformational transformations in fibrin-monomer molecule result in diminishing the complementarity of lateral binding sites; less specific D--D contacts remaining the only means of the "end-to-end" association. Experimentally obtained data give evidence that polymerization region is shifted towards much lower urea concentration, fibrinopeptide B being preserved. Therefore, the possibility of several conformational states of protein molecules during fibrinogen--fibrin transformation is discussed. It is supposed that changes in structure concern not only the central E-, but also the peripheral D- or alpha C-domains.