The interaction between fibrinogen and thrombin with the formation of fibrin is a key stage in the formation of a blood clot during blood coagulation, with the morphology of the clot being determined by the concentrations of the components. It has previously been shown that, at low thrombin concentrations, long fibrillar aggregates of fibrin are formed. In this paper, we consider the features of the formation of fibrin aggregates in the surface layers of aqueous solutions at relatively low concentrations of both fibrinogen (5 x 10(-9)-2 x 10(-7) M) and thrombin (5-25 U/L). At a low thrombin concentration (5 U/L), non-monotonic dependences of elasticity are observed probably due to the unfolding of protein macromolecules in the surface layer. At higher enzyme concentrations (10 and 25 U/L), these dependences become monotonic, and the dynamic surface elasticity reaches higher values that exceed those for pure protein solutions. Atomic force microscopic examinations have suggested that this effect is caused by the formation of fibrillar aggregates in the surface layer.
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