Enzymatic properties of plasmins converted from acid-treated and native Glu- and Lys-plasminogens by urokinase

Effects of tranexamic acid on fibrinolysis, fibrinogenolysis and amidolysis

When Glu-plasminogen (Glu-plg) was activated by urokinase (UK) in the presence of fibrinogen or fibrinogen plus tranexamic acid (1 mM), or else tranexamic acid (1 mM), the activation as measured by the hydrolysis of S-2251 was enhanced by tranexamic acid or fibrinogen or both. When plasma or clotted plasma was activated by UK in the presence of 1 mM tranexamic acid, fibrinolysis was completely inhibited. When Lys-plg was activated by UK in the presence of tranexamic acid and fibrin or fibrinogen, fibrinolysis was completely inhibited by 1 mM tranexamic acid, but some inhibition of fibrinogenolysis was observed. The release of B beta 15-42 from fibrin in clotted plasma activated by UK was inhibited to some extent by 1 mM tranexamic acid. The release of B beta 15-42 from fibrin after UK-activation of Lys-plg was partly inhibited by tranexamic acid. In conclusion, tranexamic acid in the concentration of 1 mM enhanced amidolysis, but inhibted fibrinolysis measured by the generation of fibrin-degradation products. Fibrinogenolysis and the release of B beta 15-42 from fibrin were partly inhibited.

Effects of pH on the conformation and activation of plasminogen

Glu-plasminogen (plg) or Lys-plg solution was kept at pH 2.0 for various time intervals, and then readjusted to pH 7.0. The activation rate and conformational changes of such acid-treated plg were measured using the hydrolysis of S-2251, spectrofluorometry and spectropolarimetry (circular dichroism). The activation rate of acid-treated Glu-plg increased after readjustment to pH 7.0. The increase was not reversible even after keeping acid-treated Glu-plg for 24 hrs at neutral pH. The activation rate of acid-treated Lys-plg rather decreased. The fluorescence intensity at 340 nm of acid-treated plg decreased, and the intensity of fluorescence induced by the interaction of plasminogen with ANS (1-anilino-8-naphthalene sulfonate) increased after keeping plasminogen for longer than 24 hrs at pH 2.0. Circular dichroism spectra indicated that the secondary and tertiary structure of Glu-plg changed after acidification, and that only the tertiary structure of Lys-plg changed.

Effects of fibrinogen and fibrin on the activation of Glu- and Lys-plasminogen by urokinase

Glu- and Lys-plasminogen (plg) were mixed with fibrinogen or fibrinogen plus thrombin in the presence of various units of urokinase (UK) and S-2251 (H-D-Val-Leu-Lys-pNA). Time course of the hydrolysis of S-2251 and the increment of OD405/min were monitored by using a spectrophotometer. Glu-plg was activated better by UK in the presence of fibrinogen and fibrin than in their absence. The effects of fibrin were larger than those of fibrinogen in the activation of Glu-plg. When Lys-plg was used for the similar experiments, the activation rate of Lys-plg was slightly increased in the presence of fibrinogen and fibrin (fibrin greater than fibrinogen), but their effects were smaller than in the case of the activation of Glu-plg.

The activation of two isozymes of glu-plasminogen (I and II) by urokinase and streptokinase

Glu-plasminogen (Glu-plg) was eluted through lysine-Sepharose by using a gradient of 6 aminohexanoic acid, and two peaks corresponding to Glu-plg I and II were obtained. Glu-plg I has a molecular weight of 93,000 and Glu-plg II has a molecular weight of 89,000. When these plgs were activated by urokinase (UK) or streptokinase (SK) in the presence of S-2251 (H-D-Val-Leu-Lys-pNA0, the hydrolysis of S-2251 by Glu-plg I activated by UK or SK was larger than that by Glu-plg II activated by UK or SK. The results of SDS-PAGE indicate that the conversion of Glu-plg I to plasmin by UK was faster than that of Glu-plg II. It may be concluded that Glu-plg I is activated better to plasmin by activators than Glu-plg II.

Potentiation of the activation of Glu-plasminogen by streptokinase and urokinase in the presence of fibrinogen degradation products

When Glu-plasminogen was activated by streptokinase (SK), the presence of early degradation products of fibrinogen (FgDP) enhanced the rate of activation. When various fragments of FgDP were fractionated, FgDP-Y and E fragments had a potentiating activity while D fragment did not. When Glu-plasminogen was activated by urokinase (UK), the activation rate was enhanced by every fragment of FgDPs, i.e. X, Y, D and E. Although both D and E fragments seem to be able to bind with lysine binding sites of Glu-plasminogen, and to enhance the activation rate by UK, only binding of E fragment with plasminogen can result in enhancement of the activation of Glu-plasminogen by SK.