[Structural transformations of fibrin oligomers].

The morphology of equilibrium of soluble fibrin oligomers at different stages of assembly was studied. Results of Rauleigh's light scattering, analytical ultracentrifugation and viscosimetry show that fibrin-polymers throughout the entire homology range present rigid, rod-like structures dispersed by weight and dimensions. It was shown, that along with the traditional double-stranded chain protofibrills, where the monomer molecules are connected "end-to-center", there is an alternative variant, which is a result of single-stranded chain dimerization, where the monomers are formed up in an "end-to-end" fashion. Identity of physicochemical features of fibrin oligomers obtained by means of different enzyme activation of fibrinogen indicates that E1 and E2 sites interact with the complementary D1 and D2 sites only at the stage of protofibrill formation. It is suggested that the lateral aggregation is initiated by other sites that exist in fibrinogen and fibrin-monomer molecules in an accessible state. Thermodynamic reasons for the cooperative ability of protofibrill aggregation processes and gel-formation are discussed.