Activation of Glu-plasminogen by urokinase in the presence of fibrinogen, fibrin, and SK-potentiator

Maggot Kinase and Natural Thrombolytic Proteins

Thrombolytic enzymes constitute a class of proteases with antithrombotic functions. Derived from natural products and abundant in nature, certain thrombolytic enzymes, such as urokinase, earthworm kinase, and streptokinase, have been widely used in the clinical treatment of vascular embolic diseases. Fly maggots, characterized by their easy growth and low cost, are a traditional Chinese medicine recorded in the Compendium of Materia Medica. These maggots can also be used as raw material for the extraction and preparation of thrombolytic enzymes (maggot kinase). In this review, we assembled global research reports on natural thrombolytic enzymes through a literature search and reviewed the functions and structures of natural thrombolytic enzymes to provide a reference for natural thrombophilic drug screening and development.

Kringle domains and plasmin denaturation

The rate of plasmin denaturation was in the order of Lys-plasmin greater than miniplasmin greater than microplasmin. Fibrinogen degradation products (FDP) dose dependently increased the denaturation rate of Lys-plasmin and mini-plasmin with a maximal rate constant at the FDP/plasmin ratio of about 0.5. The denaturation rate constant of microplasmin was not affected. FDP increased the rate of plasmin denaturation was in parallel with its effect on the interaction among kringle domains. Without FDP only trace amounts of plasminogen dimer could be detected by cross-linking with bis-(sulfo-succinimidyl)-suberate followed by SDS gel electrophoresis. In the low concentration of FDP significant amounts of oligomers of Glu-, mini-plasminogens, kringle 1-3 and kringle 1-5 were observed. High concentration of FDP, however, decreased plasminogen oligomer.

Kinetic analyses of the activation of Glu-plasminogen by urokinase in the presence of fibrin, fibrinogen or its degradation products

The kinetics of the activation of Glu-plasminogen (Glu-plg) and Lys-plasminogen (Lys-plg) by urokinase (UK) were studied in purified systems. The activation of plasminogen by UK in the purified systems followed Michaelis-Menten kinetics with a Michaelis constant (Km) of 1.45 microM and a catalytic rate constant (kcat) of 0.93/sec for Glu-plg as compared to 0.25 microM (Km) and 0.82/sec (kcat) for Lys-plg. In the presence of fibrin and fibrinogen or its plasmin degradation products (fragment D and fragment E), Km for Glu-plg hardly changed, whereas kcat for Glu-plg increased. Effect on increase in kcat was in the order of fibrin greater than fibrinogen greater than D greater than E. Fibrin, fibrinogen, D and E did not influence the activation of Lys-plg by UK. These results indicate that Glu-plg bound to fibrin, fibrinogen, D or E becomes easily activatable by UK. The activation of Lys-plg, however, is not influenced in the presence of fibrin, fibrinogen, D or E.

Differences in the activation rates of plasminogen by tissue plasminogen activator and urokinase

The activation of a native form of plasminogen (Glu-plg) by tissue plasminogen activator(t-PA) was enhanced when the plasma was clotted by the addition of thrombin or thrombin plus Ca++. Cross-linking of fibrin in the clotted plasma did not inhibit the fibrin-associated enhancement of the activation of plasminogen by t-PA. When fibrinolysis induced by t-PA in the clotted plasma was measured using enzyme immunoassay, lysis of non cross-linked fibrin in the clotted plasma was faster than lysis of cross-linked fibrin, however such decrease in the extent of fibrinolysis was observed in cross-linked fibrin even in the absence of alpha 2antiplasmin (alpha 2AP) in a purified system. When Glu- or Lys-plg (modified plg) was activated by t-PA, the presence of fibrin enhanced significantly the extent of activation of both Glu- and Lys-plg, but the activation of Glu-plg by urokinase (UK) was enhanced in the presence of fibrin. The activation of Lys-plg by UK was rather inhibited in the presence of fibrin.

Release of B beta peptides from fibrinogen or fibrin in the presence of alpha 2 antiplasmin

When Glu-plasminogen (plg) was activated by urokinase (UK) in the presence of fibrinogen or fibrin, B beta peptides (B beta 1-42) were released faster from fibrinogen than from fibrin (B beta 15-42). These results were contrary to faster release of B beta 15-42 from fibrin in the UK-activated clotted plasma in comparison to the release of B beta 1-42 from UK-activated plasma. The addition of plasma or lysine-Sepharose pass through fraction to the above system resulted in faster release of B beta peptides from fibrin than fibrinogen. The addition of alpha 2 antiplasmin (alpha 2AP) to the mixture of Glu-pig, UK and fibrinogen or fibrin resulted in faster release of B beta peptides from fibrin than from fibrinogen. These results indicate that fibrin protected plasmin from inactivation by alpha 2AP, leading to cleavage of Arg(42)-Ala(43) bond in beta-chain of fibrin which seems to be less susceptible to plasmin than the same bond in fibrinogen.

[Plasminogen activators: general aspects and recent developments]

Considerable interest in plasminogen activators as human thrombolytic drugs has stimulated rapid biotechnologic progresses. These enzymes have been classified in two immunochemically distinct groups: "urokinase-like" activators or u-PA which do not interact with fibrin and "tissue activator-like" activators or t-PA which interact with fibrin. Plasminogen activators are widely distributed in normal and malignant tissues and they are implicated in various physiological and pathological processes. They maintain the functional integrity of the vascular system and their presence may be of importance in tissue remodeling and cell migration. Urokinase and streptokinase are used in human thrombolytic therapy. However, the properties displayed by t-PA suggest that this enzyme may be a superior fibrinolytic agent. The primary structures of urokinase and t-PA are known; both enzymes have been synthesized by DNA technology. In order to produce t-PA in large quantities by gene cloning, intensive studies are conducted by pharmaceutical industries. Clinical trials using t-PA for dissolving thrombi in coronary heart disease, strokes and pulmonary embolism are in progress. This review presents the molecular and structural properties of plasminogen activators, as well as related physiological, pathological and therapeutic aspects.

Quantitative characterization of the binding of plasminogen to intact fibrin clots, lysine-sepharose, and fibrin cleaved by plasmin

The binding of human Glu- and Lys-plasminogens to intact fibrin clots, to lysine-Sepharose, and to fibrin cleaved by plasmin was quantitatively characterized. On intact fibrin clots, there was one strong binding site for Glu-plasminogen with a dissociation constant, Kd, of 25 microM and one strong binding site for Lys-plasminogen with a Kd of 7.9 microM. In both cases, the number of plasminogen binding sites per fibrin monomer was 1. Also, a much weaker binding site for Glu-plasminogen was observed with a Kd of about 350 microM. Limited digestion of fibrin by plasmin created additional binding sites for plasminogen with Kd values similar to the binding of plasminogen to lysine-Sepharose. This was predictable given the observations that plasminogen binds to lysine-Sepharose and can be eluted with epsilon-aminocaproic acid [Deutsch, D.G., & Mertz, E.T. (1970) Science (Washington, D.C.) 170, 1095-1096] and that plasmin preferentially cleaves fibrin at the carboxy side of lysyl residues [Weinstein, M.J., & Doolittle, R.F. (1972) Biochim. Biophys. Acta 258, 577-590], because the structures of the lysyl moiety in lysine-Sepharose and of epsilon-aminocaproic acid are identical with the structure of a COOH-terminal lysyl residue created by plasmin cleavage of fibrin. The Kd for the binding of Glu-plasminogen to lysine-Sepharose was 43 microM and for fibrin partially cleaved by plasmin 48 microM. The Kd for the binding of Lys-plasminogen to lysine-Sepharose was 30 microM. With fibrin partially cleaved by plasmin, there were two types of binding sites for Lys-plasminogen, one with a Kd of 7.6 microM and the other with a Kd of 44 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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

Glu-plasminogen I (Glu-plg I: with two carbohydrate chains) and Glu-plg II (with one carbohydrate chain) were separated by a gradient elution of 6 aminohexanoic acid (6AHA) through lysine-Sepharose. Each preparation was excited with ultraviolet light of wave length at 291 nm. The intensity of fluorescence was measured at 340 nm. The intensity of fluorescence increased to a small extent at 0.02 mM of tranexamic acid (t-x) for Glu-plg I and then quickly increased from 0.1 mM of t-x to reach the peak at 0.6 mM. The intensity of fluorescence for Glu-plg II started to increase at 0.2 mM to reach the peak at 0.7 mM. No small increase of fluorescence was observed at less than 0.2 mM of t-x for Glu-plg II. Kdobs of Glu-plg I for t-x and 6AHA were 0.34 mM and 1.35 mM, respectively, whereas Kdobs of Glu-plg II for t-x and 6AHA were 0.46 mM and 3.3 mM, respectively. When Glu-plg I and II were activated by urokinase (UK) and the hydrolysis of S-2251 was measured, the extent of hydrolysis increased in the presence of t-x and 6AHA. The rate of the increase of S-2251 hydrolysis (thus activation rate of Glu-plg I and II with UK) increased in parallel with increase in fluorescence intensity of Glu-plg I and II in the presence of omega-aminoacids. In conclusion, changes in the activation rate with UK and in fluorescence intensity were observed at lower concentrations of omega-aminoacids for Glu-plg I than for Glu-plg II.

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.

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.

Activation pathway of glu-plasminogen to Lys-plasmin by urokinase

When Glu-plasminogen (Glu-plg) was incubated with plasmin for various time intervals, and the mixture was activated by urokinase (UK), the activation rate increased gradually as incubation time increased. The presence of fibrin not only enhanced the activation rate of Glu-plg but also that of proteolytically modified form to some extent. The results of SDS-PAGE indicated that the release of N-terminal peptides from Glu-plg or Glu-plasmin takes place gradually when the concentration of plg was about 1 microM, and that Glu-plasmin I of larger molecular weight is more slowly converted to Lys-plasmin than Glu-plasmin II of smaller molecular weight. The amounts of carbohydrate moieties on the heavy chain of plasmin may influence the release of N-terminal peptide from Glu-plasmin. Kinetic studies indicate that Lys-plasmin has smaller km than Glu-plasmin, thus the former being better enzymatically than the latter.

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.