On the interaction of fibrinolysin (plasmin) with the inhibitors antifibrinolysin and soybean trypsin inhibitor

Abstract A turbidimetric technique was used to measure the activity of fibrinolysin (FL). The substrates used were fibrinogen and the fibrin derivatives produced during visual lysis of fibrin. With fibrinogen as a substrate, the Michaelis constant was estimated to be 3.6 × 10 −5 M . Inhibition of fibrinolysis and the process after visual lysis was obtained with crystalline soybean trypsin inhibitor and an antifibrinolysin preparation from bovine plasma (estimated M.W. 57,000). Th calculated dissociation constant of the complex between FL and antifibrinolysin was 7 × 10 −7 . The dissociation constant for the complex between FL and trypsin inhibitor must be considerably less. Effects of heparin and epsilon-amino-caproic acid were also studied. We have estimated that at low FL concentrations in plasma the concentrations of bound FL is one hundred times larger than the concentration of free FL. The increase in lysis times in the presence of inhibitors can be partly reversed with mercurials.