Characterization of soluble polymerized fibrin formed in the presence of excess fibrinogen fragment D

Abstract

Polymerization of [human] fibrin is inhibited in the presence of excess fibrinogen fragment D. The proposal that these inhibited solutions contain short linear polymers of fibrin (protofibrils) whose further polymerization is prevented as a result of attachment of a molecule of fragment D at each end was tested. Negative-stain electron micrographs, intrinsic viscosities, angular dependence of light scattering intensity, and kinetics of the increase of the scattered intensity with polymerization all were found to support the above model of the inhibited polymer and to reflect the presence of a broad distribution of the lengths of the inhibited fibrin polymers. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of polymers stabilized with .gamma.-dimer cross-links introduced by factor XIIIa demonstrates cross-linking of fragment D to fibrin oligomers. Cross-linked polymers were separated from excess fragment D by gel exclusion chromatography in 1 M urea. In the absence of urea, the purified polymers very slowly associate to fibers. The observation of the relative stability of short isolated inhibited protofibrils and the decrease or absence of inhibition of fibrin gelation when fragment D was added to solutions in which fibrin was given time to polymerize to long protofibrils demonstrate that the inhibitory effect of fragment D occurs as a result of inhibition of the 1st fibrin polymerization step.