Studies on the Ultrastructure of Fibrin Lacking Fibrinopeptide B ( 9 - Fibrin )

Release of fibrinopeptide B from fibrinogen by copperhead venom procoagulant enzyme results in a form of fibrin ($-f,brin) with weaker self-aggregation characteristics than the normal product (a/9-fibrin) produced by release of fibrinopeptides A (FPA) and B (FPB) by thrombin. We investigated the ultrastructure of these two types of fibrin as well as that of $-fibrin prepared from fibrinogen Metz (Aal 6 ArgCys). a homozygous dysfibrinogenemic mutant that does not release FPA. At 1 4’C and physiologic solvent conditions (0.1 5 mol/L of NaCI, 0.01 5 mol/L of Tris buffer pH 7.4). the turbidity (350 nm) of rapidly polymerizing a/9-fibrin (thrombin 1 to 2 U/mI) plateaued in <6 mm and formed a “coarse” matrix consisting of anastomosing fiber bundles (mean diameter 92 nm). More slowly polymerizing a 9-fibrin (thrombin 0.01 and 0.001 U/mL) surpassed this turbidity after 60 minutes and concomitantly developed a network of thicker fiber bundles (mean diameters 1 1 8 and 1 86 nm, respectively). Such matrices also contained networks of highly branched, twisting, “fine” fibrils (fiber diameters 7 to 30 nm) that are usually characteristic of matrices formed at high ionic strength and pH.