Fluorescence spectrophotometric studies on the conformational changes induced by omega-aminoacids in two isozymes of Glu-plasminogen (I and II)

Effects of heparan sulfate analogue or other sulfated polysaccharides on the activation of plasminogen by t-PA or u-PA

Effects of heparan sulfate analogue (HHS-5) and other sulfated polysaccharides on the fibrinolytic system were investigated. Activation rate of native plasminogen (Glu-plg) by tissue plasminogen activator (t-PA), urinary plasminogen activator (u-PA) and single-chain u-PA (scu-PA) was enhanced in the presence of HHS-5 dose dependently up to 10 micrograms/ml. Activation rate of Glu-plg by sct-PA was more enhanced than that by tct-PA in its presence. HHS-5 enhanced the activation of Glu-plg by t-PA or u-PA compared to the activation of Lys-plg. SDS-PAGE confirmed that the enhancement of the hydrolysis of S-2251 by the mixture of Glu-plg, sct-PA and HHS-5 was due to the facilitation of the conversion of Glu-plg to plasmin. HHS-5 only slightly enhanced the amidolytic activity of sct-PA or tct-PA. The enhancement of the activation of plasminogen by t-PA or u-PA was more significant in the presence of HHS-5 than in the presence of chondroitin sulfate C, dextran sulfate or heparin. It is possible that the enhancement of the activation of Glu-plg by activators in the presence of HHS-5 was due to the conformational change of Glu-plg upon interaction with HHS-5.

Conformational change of plasminogen: effects of N-terminal peptides of Glu-plasminogen

Seven peptides were synthesized to analyze the mechanism of the intramolecular binding of the N-terminal peptide of Glu-plasminogen (Glu-plg) to its kringles. They were Ala44-Lys50, Ala44-Glu51, Ala44-Ser49, Val17-Gly23, Lys19-Gly23, Lys19-Gln21 and Lys19-Lys20. Ala44-Lys50, Ala44-Glu51 and Lys19-Lys20.enhanced the activation of Glu-plg by tissue plasminogen activator (t-PA) or urinary plasminogen activator (u-PA). The activation of Lys-plg, however, was not influenced by these peptides. Therefore, it is suggested that these three peptides worked on Glu-plg in a similar manner as lysine analogue by making the conformation of Glu-plg looser. These peptides did not have any direct effects on u-PA and t-PA. Concerning the effect on fibrinolysis Ala44-Lys50 and Lys19-Lys20 prolonged euglobulin clot lysis time. These results indicate that Ala44-Glu51 may be a responsible binding site in the N-terminal portion of Glu-plg, and LBS of kringle 1 or 4 is the binding site of N-terminal portion of Glu-plg.

Effects of N-terminal peptide of Glu-plasminogen on the activation of Glu-plasminogen and its conversion to Lys-plasminogen

In order to analyze the mechanism of the intramolecular binding of the N-terminal peptide of Glu-plasminogen (Glu-plg) to its kringles, which results in its tight conformation, we synthesized peptides of the N-terminal portion of Glu-plg molecules and analyzed their effects on the activation of Glu-plg and its conversion to Lys-plasminogen (Lys-plg) by plasmin. Three peptides of Ala44-Lys50, Ala44-Glu51 and Ala44-Ser49 were synthesized in order to examine the effect of lysine residue in the peptide. Ala44-Lys50 and Ala44-Glu51 enhanced the activation of Glu-plg by urokinase, whereas the activation of Lys-plasminogen (Lys-plg) was slightly inhibited. The conversion of Glu-plg to Lys-plg by plasmin was also enhanced by these peptides. The results suggest that Ala44-Lys50 and Ala44-Glu51 worked on Glu-plg in a similar manner as lysine analogues by making its conformation looser. The third peptide Ala44-Ser49 did not have any effect on the activation of Glu-plg by urokinase or the conversion of Glu-plg to Lys-plg by plasmin. Ala44-Lys50 residue of Glu-plg is, therefore, strongly implicated as a candidate for the responsible site of the intramolecular binding in Glu-plg.

Inhibition by tranexamic acid of the conversion of single-chain tissue plasminogen activator to its two chain form by plasmin: the presence on tissue plasminogen activator of a site to bind with lysine binding sites of plasmin

The addition of tranexamic acid inhibited the conversion of single chain tissue plasminogen activator (sct-PA) to its two chain form (tct-PA) by plasmin. Increase in the concentrations of tranexamic acid resulted in more inhibition of the conversion, with 50% inhibition being obtained at 0.251 mM of the concentration of tranexamic acid. The addition of the fragments of plasminogen such as kringle 1 to 3 (K1-3), and K4 resulted in the facilitation of the conversion of sct-PA to tct-PA by plasmin. The addition of tranexamic acid to the mixture of sct-PA and K4 inhibited the rate of the conversion of sct-PA by plasmin. These results suggest that binding of lysine binding sites of plasmin or plasminogen with sct-PA enhanced its conversion to tct-PA by plasmin, and that there is a site on a t-PA molecule to bind to plasminogen or plasmin.

Autoradiographic and immunoblotting analyses of the activation pathways of plasminogen by urokinase and tissue plasminogen activator in the plasma or clotted plasma

The activation pathway of Glu-plasminogen (Glu-plg) was analyzed by using immunoblotting and autoradiography. Glu-plg was slowly activated to Glu-plasmin by urokinase (UK) and tissue plasminogen activator (t-PA) in the plasma. Significant amounts of a complex of alpha 2AP with plasmin were found. On the other hand, UK and t-PA rapidly activated Glu-plg in the clotted plasma. The major form of plasmin was Lys-form, and significant amounts of alpha 2M complexed with plasmin were found. A complex of alpha 2AP with plasmin was not so significantly formed in the clot, confirming ineffective inhibition of plasmin by alpha 2AP in the presence of fibrin. Glu-plg was directly activated by UK or t-PA to Glu-plasmin and further to Lys-plasmin in the plasma or clotted plasma.

Effects of fibrin on the enhanced activation of plasminogen by urokinase and tissue plasminogen activator: role of cross-link

When human plasma was activated by urokinase (UK) in the presence of thrombin, thrombin plus Ca++, Ca++ or in their absence and the plasmin activity was measured by the hydrolysis of S-2251, plasmin activity was higher in the presence of cross-linked or non cross-linked plasma clot. The results of similar experiments utilizing plasma after severe exercise indicated that the hydrolysis of S-2251 by plasma containing tissue plasminogen activator (t-PA) was also higher in cross-linked or non cross-linked plasma clot. Fibrinolysis was faster in thrombin-induced plasma clot, but was later shown significantly in plasma clot induced by thrombin and Ca++, whereas practically no fibrinogenolysis was shown in plasma. When Glu-plasminogen (Glu-plg) was activated by UK in the presence of cross-linked or non cross-linked fibrin and alpha 2 antiplasmin (alpha 2AP), fibrinolysis was faster in cross-linked fibrin than non cross-linked fibrin in the presence of alpha 2AP. No fibrinogenolysis was shown either. Plasmin activity measured by the hydrolysis of S-2251 was also higher in cross-linked or non cross-linked fibrin than in fibrinogen in the presence of alpha 2AP. These results indicate that enhanced activation of Glu-plg by UK or t-PA in the presence of fibrin was a more significant event than the inactivation of plasmin in the plasma clot or purified clot by alpha 2AP cross-linked to fibrin.

Effects of tranexamic acid on the conversion of Glu-plasminogen I and II to its Lys-forms

Glu-plasminogen (Glu-plg) was incubated with plasmin. It took more than 2 hr incubation for the conversion of Glu-plg to a modified form (Lys-plg) to take place. Especially the conversion of Glu-plg II to Lys-plg II by plasmin took place very slowly. On the other hand, the conversion of Glu-plg I to Lys-plg I took place faster than that of Glu-plg II. In the presence of 1 mM tranexamic acid, the conversion of both Glu-plg I and II to their Lys-forms by plasmin was accelerated and completed in 30 min incubation. Fifty percent increase in the rate of the conversion of Glu-plg I to Lys-plg I was observed in the presence of 0.18 mM tranexamic acid. For the conversion of Glu-plg II to Lys-plg II, larger concentration of tranexamic acid was needed. Another observation was that tranexamic acid protected the degradation of plasminogen by plasmin, indicating the involvement of the lysine binding sites (LBS) of plasmin in the proteolytic attack against plg.

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.

Glu-plasminogen I and II: their activation by urokinase and streptokinase in the presence of fibrin and fibrinogen

Two isozymes of a native form of human plasminogen (plg), Glu-plg I and II, were isolated. Glu-plg I or II was activated by urokinase (UK) or streptokinase (SK) in the presence of fibrinogen or fibrin. The activation of Glu-plg I was enhanced more than that of Glu-plg II in the presence of fibrin. Fibrin caused better activation of both Glu-plg I and II than fibrinogen. When fibrinolysis or fibrinogenolysis was measured, fibrin was degraded faster than fibrinogen after the activation of Glu-plg I and II by UK. These results suggest that the activation of Glu-plg I was enhanced more than that of Glu-plg II in the presence of fibrin or to less extent fibrinogen.

The activation of Glu- and Lys-plasminogens by streptokinase: effects of fibrin, fibrinogen and their degradation products

Studies were performed on the activation of a native form of human plasminogen (Glu-plg) or its degraded form (Lys-plg) by streptokinase (SK) in the presence of fibrin, fibrinogen, SK-potentiator, fragment D or E. When Glu-plg (0.1 microM) was activated by 0.5 u/ml of SK in the presence of 100 micrograms of S-2251 and 0.1 microM of fibrin, fibrinogen or their degradation products (potentiating agents), fibrin enhanced the rate of the hydrolysis of S-2251 to the largest extent. Fragments D and E only slightly enhanced it. The order of effectiveness of enhancement was fibrin greater than SK-potentiator greater than fibrinogen greater than D greater than E. When Lys-plg (0.1 microM) was activated by 0.5 u/ml of SK in the presence of potentiating agents, SK-potentiator enhanced the hydrolysis of S-2251 to the largest extent. The enhancement was far less in comparison to the enhancement of the hydrolysis by Glu-plg and SK. The measurement of delta OD405/min at the time of 50% hydrolysis of the substrate was performed in order to compare the effects of concentrations of potentiating agents. The maximum enhancement was obtained at almost an equimolar ratio of plasminogen and fibrin. Fifty percent enhancement was obtained at 0.05 microM for SK-potentiator, 0.072 microM for fibrinogen, 0.21 microM for D and 0.35 microM for E. Fibrin caused the largest extent of enhancement among other potentiating agents. These results may indicate that a trimolecular complex between SK, plasminogen and potentiating agents hydrolyzes S-2251 more effectively than SK-plasminogen complex, thus a trimolecular complex being a better activator than SK-plasminogen complex. Although D and E enhanced only slightly the rate of hydrolysis of S-2251 at equimolar ratio to plasminogen, increase in their concentration resulted in the same extent of enhancement as shown in the presence of fibrinogen or SK-potentiator.

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.

Fluorescence polarization and spectropolarimetric studies on the conformational changes induced by omega-aminoacids in two isozymes of Glu-plasminogen (I and II)

Conformational changes of two isozymes of Glu-plasminogen (Glu-plg I and II) induced by omega-aminoacids were studied by using fluorescence polarization and spectropolarimetry. The rotational relaxation times (Pn) of FITC labeled Glu-Plg I and II decreased in the presence of 6 aminohexanoic acid (6AHA) or tranexamic acid (t-x), which may mean increase in Brownian motion of FITC labeled region (possibly N-terminal region) of Glu-plg I and II when 6AHA or t-x binds with lysine binding sites (LBS) of these plasminogens. Glu-plg II seems to have longer rotational relaxation time compared to that of Glu-plg I, which may mean smaller extent of Brownian motion of FITC labeled region of Glu-plg II in comparison to that of Glu-plg I. The far ultraviolet circular dichroism (CD) spectra indicate that there may be some difference in the polypeptide backbone between Glu-plg I and II, possibly more of beta-structure and less of random coil structure in Glu-plg II in comparison to Glu-plg I. The presence of 6AHA or t-x gave rise to larger change of the negative ellipticity at around 208 nm in Glu-plg I in comparison to its change in Glu-plg II, which may mean the larger extent of conformational change of Glu-plg I induced by 6AHA or t-x than that of Glu-plg II.