The Pre-Gelation Phase Of Fibrin Aggregation

So far, fibrin aggregation in solution has been studied by either static or dynamic light scattering and the data analyzed using a linear chain model. In the present study we have combined static and dynamic light scattering and compared the data with a model predicting a sol-gel transition. Fibrinogen solutions (cone. 2 mg/ml, Tris-NaCl buffer 0.15 M, pH 7.4) were incubated at 20°C with small amounts of Reptilase or thrombin, extending the polymerization process to 4-6 hours. The scattered intensity and correlation function were recorded for scattering angles 30° ≤ θ ≤ 150°. The measured data were compared with model calculations based on the Flory-Stockmayer distribution which predicts a sol-gel phase transition. This distribution is determined by a parameter λ indicating the extent of aggregation, λ = 0 corresponding to the monomeric solution and λ = 1 indicating sol-gel transition. Good agreement could be found for 75 nm long monomeric units aggregating: a) end-to-end for the beginning of the aggregation (0 0.3) and b) in a staggered overlap pattern as proposed by Ferry for the progressing polymerization (0.3 ≤ λ < 1). Prior to the gel point (λ = 1) no systematic difference was observed between the data obtained after activation with thrombin which splits both peptides A and B from fibrinogen and Reptilase which exclusively liberates fibrinopeptide A. This confirms that the release of fibrinopeptide A is the essential prerequisite for the aggregation process.