Inhibition of fibrin polymerization by fibrinogen proteolysis products

The action of fibrinogen proteolysis products in inhibiting fibrinogen-fibrin conversion by thrombin has excited considerable interest because of its possible significance in blood coagulation. This reaction has been investigated by following the polymerization of highly purified fibrin monomer, in the presence and absence of fibrinogen proteolysis products, by a spectrophotometric procedure. Fibrinogen proteolysis products inhibited polymerization at low ratios of proteolysis products/monomer, and both early and late phases of polymerization were equally affected. Polymerization rates of fibrin monomer, as apart from the gel point, were little influenced by reaction temperature over the range 15–35 C, and the degree of inhibition produced by fibrinogen proteolysis products was likewise independent of temperature. A linear relationship was demonstrated between the degree of inhibition to polymerization and the ratio of fibrinogen proteolysis products to monomer. It is suggested that the inhibitory mechanism involves the coupling of fibrinogen proteolysis products with monomer in a "competitive" manner.