Elektronenmikroskopische Untersuchungen zur Gestalt und zum makromolekularen Bau des Fibrinogenmolek�ls und der Fibrinfasern

Molecular and supramolecular structure of adsorbed fibrinogen and adsorption isotherms of fibrinogen at quartz surfaces

The adsorption of fibrinogen to quartz surfaces was measured by ellipsometry, ELISA, and electron microscopy. The initial adsorption at low concentrations was diffusion rate limited as determined by the ELISA and by counting the number of adsorbed molecules at electron micrographs. From ellipsometry, ELISA, and electron microscopy measurements it was found that the surface concentration of adsorbed fibrinogen increased continuously over four decades in bulk concentration of fibrinogen. At a hydrophilic quartz surface a plateau level of the adsorption isotherm was found at a surface concentration of 0.1 pmol/cm2 where the adsorbed molecules had a mean intermolecular distance of 10 +/- 5 nm between neighbors. At higher surface concentrations the molecules were densely packed and formed a layer where single molecules could not be identified. Adsorbed fibrinogen showed different structure at hydrophobic and hydrophilic quartz surfaces. At a hydrophilic surface, the fibrinogen molecules appeared as a 46 nm nodose rod consisting of 6-7 nodes with a diameter of 4 nm. At a hydrophobic surface, the molecule appeared as a binodular or trinodular rod with a node diameter of 5-9 nm, connected with a thin filament to form a 40-nm rod. Adsorption from higher concentrations of fibrinogen in solution resulted in adsorbed spheric structures with a diameter of 18-24 nm at the hydrophobic surface and in end-to-end polymers at the hydrophilic quartz membrane.

Quantitation of the inhibitory effect of fibrinogen and its degradation products on fibrin polymerization

Anticlotting activities of fibrinogen and its plasmin degradation products--fragments X,Y and D--have been measured. On the molar basis fragments Y and D are found equally active whereas fragment X acts about 2 times stronger. We suggest that the inhibitory effect depends on a set of specific binding sites characteristic of domain D. As fragment X possesses two such sets its activity is twice as high as that of the single-set fragments Y and D. In spite of its two domains D fibrinogen inhibits clotting much weaker than fragment X. This is probably due to the presence in fibrinogen of large COOH-terminal sections of the two A infinity-chains interfering with the inhibitory effect. The possible role of these A infinity-chain sections in fibrinogen-fibrin system is discussed.

Fibrinogen-fibrin transformations characterized during the course of reaction by their intermediate structures. A light scattering study in dilute solution under physiological conditions

Intermediate structures of human fibrin formed under physiological conditions were investigated by means of light scattering in the course of the polymer/network formation. Very low fibrinogen concentrations (c = 0.03--0.13 mg/ml) were used to lower the polymerization rate, and thrombin at five concentrations (0.0085--0.04 N.I.H./ml) was used for initiation. The light scattering data were evaluated from (i) a Zimm plot, (ii) a Holtzer plot, i.e., hRtheta/Kc vs. h2, and (iii) a Kratky plot, i.e., h2Rtheta/KC vs. h2. In the beginning of the polymerization process rod-like structures are formed. The dimensions of the rod-like monomeric unit in the fibrin polymer are 112 X 3.9 nm and agree with the dimensions of fibrinogen, which also was found to be a thin rod of 105 +/- 10 nm length and 3.9 nm diameter. The mass per unit length, obtained from the asymptote in the Holtzer plot, initially increases only slightly but for high thrombin concentrations increases steeply when a critical length of 1000 nm is exceeded. At this point also the total scattering behaviour changes considerably. The upturn in the Zimm plot and the occurrence of a maximum in the Kratky plot are clear indications for the onset of branching. At low thrombin concentrations the kink in the curve of Mw/Lw against Mw becomes smoothed out because of nonspecific side-by-side aggregation of fibrin strands. The results are discussed and compared with earlier findings by others, and lead to the following conclusions. (i) Fibrinogen is a polymer with some flexibility and can exist in conformations of a stretched rod 105 nm in length, a folded rod of 45 nm in length, and a banana-like conformation of 94 nm circumference. (ii) Under the conditions of the present work, fibrinogen has the thin stretched rod conformation, and has the same dimensions as the repeating unit in the fibrin polymer. (iii) After approx. 10--12 units, end-to-end aggregated monomer branching occurs. (iv) The end-to-end aggregation is promoted by the cleavage of A peptides, branching is caused by the cleavage of B peptides while side-by-side aggregation of strands is caused by nonspecific van der Waals interaction.

Proteolytic fragmentation of fibrinogen. II. kinetic modeling of the digestion of human and bovine fibrinogen plasmin or trypsin

The kinetic data presented in the previous paper (Mihalyi, E., et al. (1976), Biochemistry 15, preceding paper in this issue), with respect to the fragmentation of human the bovine fibrinogen by either plasmin or trypsin, were compared with several chemical kinetic models. The models were derived mathematically on the basis of the three-nodular structure of fibrinogen (Hall, C.E., and Sayter, H.S. (1959), J. BiophysBiochem. Ctyol. 5, 11) and the asymmetrical cleavage sequence first proposed by Marder, V.J., et. al. ((1969) J. Biol. Chem. 244, 2111). The parameters were determined by nonlinear curve fitting. The whole process could be described accurately by only two rate constants. Several variant models were tested and, although a clear cut choice cannot be made, one of these, the protected three-bonds model, appears to give the best fit in most cases. This model assumes that the chain segment that distinguishes F from X protects certain other chains (the bonds) from proteolytic cleavage.