The Role of Plasmin for Kinin Formation in Human Plasma / Die Bolle von Plasmin bei der Eininbildung in menschlichem Plasma
Plasmin has been envisaged as a kininogenase by several authors whereas others did not see any kinin-liberating effects. An explanation for the existing discrepancies was offered by the finding that in dog plasma (fractions) plasmin induced kinin formation only indirectly, by activating plasma kallikrein (Vogt ). However, Back and Steger  as well as Henriques et al.  reported kinin liberation in incubates of plasmin and kininogen preparations which were apparently free of (pre-)kallikrein. It has now been found that activation and stabilisation of plasmin in human plasma, by treatment with streptokinase and p-iodobenzoate (von Kaulla ) leads to kinin formation. The induced kinin-liberating potency is lost, however, after heating the plasma to 61°, at pH 4, for 60 min, although this treatment does not impair the plasmin activity as measured by caseinolysis. Conversely, the kinin-liberating potency is not inhibited by lima bean inhibitor (LBI) (0.5–1.0 mg/ml) although this inhibitor blocks plasmin (Back and Steger ). It is concluded, therefore, that the kinin formation by plasmin activated in human plasma is effected indirectly, by activation of an enzyme which like plasma kallikrein but unlike plasmin, is destroyed by heating and not inhibited by LBI.