The solubility and polymerization of preformed human des-AA and des-AABB fibrin monomers (prepared from fibrinogen in urea by insolubilized reptilase or thrombin) was studied. In solutions of purified fibrinogen, des-AA fibrin to approximately 17% of the fibrinogen concentration could be kept solubilized (I=0.15, pH 7.4, temp.+20°C) If calcium ions (2.5 mM) were present, or if fibrinogen-boosted serum was used, only 3.5% were soluble. The solubility of des-AA fibrin monomers in fibrinogen-boosted, heat-defibrinogenated, citrated plasma was about 10%. Since the ionic strength of fibrinogen-boosted serum and fibrinogen-boosted, heat-defibrinogenated, citrated plasma was measured to be nearly identical, the higher fibrin solubility in the latter milieu is either due to: the presence of citrate, or the calcium-binding effect of citrate, or both. The corresponding figures for the solubility of des-AABB fibrin monomers were 13%, 3% and 8%, respectively. In the abscence of fibrinogen, identical polymerization rates for both types of fibrin monomers (as judged by light scattering at 605 nm) were observed, but the polymerization of des-AA fibrin monomers was more retarded by the presence of fibrinogen than was polymerization of des-AABB fibrin monomers, thus reflecting the higher solubility of the former. The present findings suggest that fibrinogen is capable of retarding fibrin polymerization on a molar basis. © 1979.
