Blocking of inhibition of fibrinolysin by mercurials and oxidizing agents

Abstract The effects of several substances upon inhibition of fibrinolysin by soybean trypsin inhibitor or antifibrinolysin have been studied. The decrease with time in turbidity of lysed fibrin mixtures, following the addition of saturated, neutralized ammonium sulfate, was used to measure fibrinolytic activity. Inhibitors of fibrinolysin or inhibitors with compounds to be tested for their blocking effects on the inhibitors were added immediately upon completion of visual lysis. Substances which were tested for their ability to restore inhibitory activity were added 3–3 1 2 minutes after visual lysis. Inhibition of fibrinolysin by antifibrinolysins or soybean trypsin inhibitor was blocked by low concentrations of mercurials, iodoacetate, iodine, or dichlorophenolindophenol. These agents, in the concentrations used, did not affect fibrinolytic activity in the absence of the inhibitors. The block to inhibition produced by mercurials was removed by the addition of cysteine or glutathione; the block to inhibition produced by iodine or iodoacetate was removed by cysteine, glutathione, NaHSO 3 , or Na 2 S 2 O 4 . Similar results were obtained with fibrinogen instead of lysed fibrin as the substrate for the enzyme. In additional experiments, clotting and lysing time of mixtures containing the inhibitors or inhibitors plus the blocking agents were determined.