EFFECT OF PROTEOLYTIC ENZYMES ON FIBRIN STABILIZING FACTOR

Fibrin stabilizing factor, an inactive precursor of the enzyme responsible for introducing cross-links into fibrin polymers, was exposed to the action of the following enzymes: plasmin (EC 3.4.4.14), trypsin (EC 3.4.4.4), chymotrypsin (EC 3.4.4.5) elastase (EC 3.4.4.7), pronase, thrombin (EC 3.4.4.13), reptilase, staphylocoagulase and an enzyme present in the venom of Echis carinatus. The first five enzymes have been prepared in water-insoluble forms by trapping them in a polyacrylamide gel. This allows the removal of the enzymes by centrifugation after incubation with the fibrin stabilizing factor, and their effects on the latter can be studied without the proteolytic degradation of fibrin. In agreement with the findings of others, our results indicate that besides thrombin and reptilase, a short exposure to trypsin also leads to activation of the stabilizing factor. Staphylocoagulase and the venom of E. carinatus neither activate nor destroy this factor. Prolonged incubation with trypsin, elastase and pronase destroys the fibrin stabilizing factor whereas it appears to be resistant to plasmin and is only partially destroyed by chymotrypsin. A hypothesis is presented that the activation of the fibrin stabilizing factor is due to a limited proteolysis resembling that taking place in the conversion fibrinogen to fibrin. © 1969.