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  • 1985-1989  (6)
  • Chemistry  (6)
  • Polymer and Materials Science  (6)
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  • Chemistry  (6)
  • Polymer and Materials Science  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Rheological studies of creep and creep recovery of unligated fibrin clots: Comparison of clots prepared with thrombin and ancrod (1985)
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 461-482 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanical creep and creep recovery in small shearing deformations have been studied in unligated clots formed with both thrombin and ancrod. In thrombin clots, both A binding sites (which interact with “a” sites to link monomer units within a protofibril) and B sites (which interact with “b” sites to form links between protofibrils) are exposed to enable formation of linkages; in ancrod clots, only the A sites are exposed. Fine clots (with minimal lateral aggregation of protofibrils), coarse clots (with substantial aggregation of fibril bundles), and clots of intermediate coarseness were compared. Fine thrombin clots showed less creep at short times but more creep at long times than coarse or intermediate clots and had more irrecoverable deformation relative to the initial elastic deformation. Ancrod clots had greater irrecoverable deformation than the corresponding thrombin clots, both fine and coarse. The permanent deformation in fine ancrod clots was enormous, corresponding almost to fluid character; the rate of permanent deformation was larger than that in fine thrombin clots by more than two orders of magnitude. For all types of clots, differential measurements of compliance (or its reciprocal, elastic modulus), as well as the applicability of the Boltzmann superposition principle to calculation of creep recovery, showed that the overall density of structure remained constant throughout the mechanical history; i.e., if structural elements were breaking, they were reforming at the same rate in different configurations. The possibility that the weakness of ancrod clots is attributable to partial degradation of α-chains rather than absence of Bb linkages was eliminated by comparisons of clots made with thrombin, ancrod, and ancrod plus thrombin; the last two showed identical partial degradation of α-chains (by gel electrophoresis), but the first and third had essentially identical initial elastic moduli and creep behavior. Two alternative mechanisms for irrecoverable deformation in fine clots are discussed, involving rupture of protofibrils and slippage of twisted segments, respectively.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360240304
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Gel formation by fibrin oligomers without addition of monomers (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1337-1344 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Soluble fibrin oligomers were formed by reacting fibrinogen with thrombin under fine clotting conditions where the action of thrombin is the rate-determining step for polymerization, and by inhibiting the reaction shortly before gelation. Oligomeric fibrin was separated from unreacted fibrinogen and small oligomers by gel permeation chromatography. Electron microscopy revealed that the largest soluble fibrin oligomers resemble the protofibrils present in fine clots, but are somewhat shorter and entirely lack the twisted, trifunctional junctions that contribute to the elastic properties of fine clots. When thrombin was added to the soluble fibrin oligomers, polymerization resumed and clots were formed at a more rapid rate than from fibrinogen at the same concentration and resulted in a less-opaque clot under coarse clotting conditions. The results confirm a prediction of a theory for the polymerization of fibrin and provide additional evidence that the final state of a coarse fibrin clot depends on the mobility of protofibrils during its formation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250712
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Interaction of the fibrinogen-binding tetrapeptide gly-pro-arg-pro with fine clots and oligomers of α-fibrin; comparison with αβ-fibrin (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 775-788 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrapeptide Gly-Pro-Arg-Pro(GPRP) was introduced by diffusion into fine unligated clots formed from human fibrinogen at pH 8.5 and ionic strength 0.45 by batroxobin (αβ-fibrin) and by thrombin (α-fibrin). The α-fibrin clots were essentially liquefied at GPRP concentrations above 1 mM and αβ-fibrin clots above 15 mM, and the degree of polymerization of the resulting oligomers decreased progressively with increasing GPRP concentration as shown by γ-γ ligation with factor XIIIa and subsequent gel electrophoresis. Much smaller concentrations of GPRP, when introduced into unligated clots by diffusion, were sufficient to modify their mechanical properties profoundly. The shear modulus of elasticity G25 measured 25 s after imposition of stress fell, for example, by a factor of 0.4 at 0.1 mM GPRP in α-fibrin and at 1.1 mM in αβ-fibrin. The rate of shear creep under constant stress and the proportion of irrecoverable deformation also increased enormously. This behavior, and the corresponding decrease in steady flow viscosity, may be interpreted in terms of competition of GPRP with A sites on the E domains of fibrin monomers for bidning to “a” sites on the D domains, resulting in a moderate increase with increasing GPRP concentration of the average proportion of severed network strands and an enormous increase in the rate at which all strands dissociate and reassociate. Reassociation of severed strands in new configurations is a necessary corollary since the differential modulus or compliance remains constant during creep and creep recovery. The greater susceptibility of α-fibrin clots to interaction with GPRP is attributed to stabilization of contacts between monomer units by Bb associations in αβ-fibrin. Ligated clots, with or without GPRP, exhibited essentially no time-dependent creep and no irrecoverable deformation, corresponding to an absence of any severance of network strands.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270506
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Interaction of fibrinogen-binding tetrapeptides with fibrin oligomers and fine fibrin clots (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1315-1336 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of fibrin, at pH 8.5 and ionic strength 0.45, and under conditions where the action of thrombin on fibrinogen was the rate-determining step, was interrupted by inactivating thrombin with p-nitrophenyl-p′-guanidinobenzoate (NPGB). Addition of the tetrapeptide Gly-Pro-Arg-Pro (GPRP) partially dissociated the fibrin oligomers as shown by subsequent ligation with Factor XIIIa and calcium ion followed by denaturation and gel electrophoresis; polyacrylamide gel electrophoresis with reduction showed a decrease in the proportion of γ-γ ligation compared with controls untreated by GPRP, and agarose gel electrophoresis showed a shift in the distribution of oligomer sizes. The dissociation was accomplished within 15 min and its extent was consistent with establishment of an equilibrium in which two molecules of GPRP react to sever an oligomer. When GPRP was introduced into fine unligated fibrin clots by diffusion, there was some dissociation as shown by differences in the degree of γ-γ ligation after treatment by Factor XIIIa; but the action of GPRP was much slower and less complete than on soluble oligomers. However, even a small amount of dissociation affected the mechanical properties of fine clots profoundly. The shear modulus (measured 25 s after application of stress) decreased progressively with increasing concentration of GPRP introduced by diffusion. The rate of shear creep under constant stress and the proportion of irrecoverable deformation also increased enormously. If the steadystate creep rate is interpreted in terms of an effective viscosity, the latter is decreased by up to three orders of magnitude by the presence of GPRP. In terms of transient network theories of viscoelasticity, the average lifetime of a network strand is greatly diminished. However, the total density of strands remains constant during creep and creep recovery as shown by constancy of the differential modulus or compliance. Removal of GPRP by diffusion only partially restores the original shear modulus and creep behavior of the original clot. Some limited data on the effect of the tetrapeptide Gly-His-Arg-Pro are also reported.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250711
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  • 5
    Electronic Resource
    Electronic Resource
    Small-angle x-ray scattering studies of fibrin film: Comparisons of fine and coarse films prepared with thrombin and ancrod (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 1011-1018 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 Å. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 Å. In unstretched fine films, only the 77-80 Å spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 Å reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 Å spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280508
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Ligation of fibrinogen by factor XIIIa with dithiothreitol: Mechanical properties of ligated fibrinogen gels (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 703-713 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Human fibrinogen (concentration 8.4 mg/mL) was ligated (cross-linked) with factor XIIIa and dithiothreitol (DTT) at pH 8.5, ionic strength 0.45. With 7.5 μg/mL of factor XIIIa alone, there was almost no γ-γ ligation, but with 2 mM DTT added, oligomers appeared, and γ-γ and Aα-Aα ligation was nearly complete after 3 days. At 38 μg/mL of factor XIIIa, some γ-γ and Aα-Aα ligation occurred even without DTT. For fibrinogen concentrations of 4.0 and 8.4 mg/mL, 38 μ/mL factor XIIIa, 2.0 mM DTT, clot-like gels formed and the shear modulus of elasticity increased slowly over several days to a constant value. The final modulus was similar in magnitude to those of ligated clots of α-fibrin (clotted by thrombin) and α-fibrin (clotted by batroxobin) under the same conditions. However, the opacity was somewhat higher; whereas in fine fibrin clots there is minimal lateral association of the protofibrils, in fibrinogen gels at the same pH and ionic strength the protofibrils (which are presumably single chains of fibrinogen monomers joined end to end at their D domains) are evidently associated in bundles (although not to the degree seen in coarse fibrin clots). Creep and creep recovery measurements showed almost perfect elastic behavior, with essentially no creep under stress and complete recovery after removal of stress. The modulus was scarcely affected by introduction of lithium bromide by diffusion to a concentration of 0.6M, which in unligated fibrin clots causes substantial softening. Whereas in fine fibrin clots (both αβ-fibrin and α-fibrin) factor XIIIa causes only γ-γ ligation, addition of 2 mM DTT produced some α-α ligation in these also.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270412
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