Relationship between release of plasminogen activator and estrogen by blastocysts and secretion of plasmin inhibitor by uterine endometrium in the pregnant pig

Pig blastocysts isolated between Days 10 and 16 of pregnancy release the protease, plasminogen activator (PA), into the medium in a time-dependent manner when cultured in vitro. Production is biphasic. The initial phase (Days 10-12) coincides with the early elongation stages, while release during the second phase (Days 14-16) occurs during a time at which the DNA content of the blastocysts is increasing markedly. Uterine flushings from these pregnant animals contain the zymogen substrate for PA, plasminogen, presumably as a serum transudate. Plasminogen is present in highest amounts at Day 12. The blastocyst, therefore, has the potential ability to generate the broadly specific protease, plasmin, within the uterine lumen. However, during this same period, the endometrium secretes an inhibitor of plasmin into the uterine lumen. In pregnant animals the amount of plasmin inhibitory activity rose 7-fold between Day 10.5, when the blastocysts were spherical, and Day 12, when they had become filamentous. At Day 12 each uterine horn contained about 3 to 4 mg of plasmin inhibitor. A similar release of inhibitor can be initiated in nonpregnant gilts given a single, intramuscular injection of estradiol valerate on Day 11 of the estrous cycle. It is suggested that the initiation of estrogen production by the elongating blastocyst triggers the release of plasmin inhibitor by the maternal endometrium and that the inhibitor serves to prevent a proteolytic cascade of reactions initiated by blastocyst PA, which might otherwise damage the uterine epithelium.

Phorbol ester and mitogens stimulate human fibroblast secretions of plasmin-activatable plasminogen activator and protease nexin, an antiactivator/antiplasmin

Tumor-promoting phorbol esters have been reported to greatly increase plasminogen activator (PA) activity produced in numerous cell types. Many of these studies have employed a widely used fibrinolysis assay for PA activity that involves large-scale dilution of cell lysates or conditioned medium (CM) into buffer containing plasminogen and the plasmin substrate 125I-fibrin. This assay indicates that phorbol ester and the mitogens epidermal growth factor (EGF) and thrombin all stimulate secretion of PA activity in our human foreskin fibroblast cultures. However, these effects are not observed in a modified fibrinolysis assay employing undiluted conditioned culture medium unless the medium is first treated at pH 3, which inactivates the secreted protease inhibitor, protease nexin (PN). Moreover, a direct assay for plasminogen activator activity based on cleavage of 125I-plasminogen indicates that conditioned culture medium contains little if any active plasminogen activator either before or after treatment of the cultures with phorbol ester or EGF. Phorbol ester and mitogens do stimulate secretion of (a) an inactive PA that can be activated by plasmin and (b) PN, which inhibits both the activated form of the PA and plasmin. Secretions of the inactive PA and PN are further correlated in that release of both is stimulated most by phorbol ester, somewhat less by EGF, and least by thrombin. Significantly, these effects are not accompanied by increases in total protein secretion. We propose that fibroblasts secrete PA in an inactive form in the presence of PN to confine PA activity to an as yet undefined location or event.

Inhibitory spectrum of mouse contrapsin and alpha-1-antitrypsin against mouse serine proteases

Contrapsin and alpha-1-antitrypsin have been recently characterized as major protease inhibitors in mouse plasma (Takahara, H. & Sinohara, H. (1982) J. Biol. Chem. 257, 2438-2446). We have studied the effects of the two inhibitors upon various serine proteases prepared from mouse tissues. Trypsin, plasmin and trypsin-like proteases of the submaxillary gland were inhibited by contrapsin but not by alpha-1-antitrypsin. On the other hand, chymotrypsin, elastase, and thrombin were inactivated by alpha-1-antitrypsin but not by contrapsin. Thus, their inhibitory spectra did not overlap each other in spite of their broad specificities. The inhibition of trypsin, chymotrypsin, and elastase was rapid and stoichiometric, whereas the inhibition of the other proteases was relatively slow. Contrapsin accounted for almost the total capacities of mouse plasma to inhibit both trypsin and submaxillary gland trypsin-like proteases, whereas alpha-1-antitrypsin was responsible for nearly all the capacities of plasma to inhibit both chymotrypsin and elastase.

Interaction of heparin with lipoproteins - role of the complex in the inactivation of thrombin and plasmin

Heparin forms a complex with human low density lipoprotein (LDL) in the presence of Ca2+. The complex is dissociable by 0.5 M NaCl. Thrombin and plasmin causes the dissociation of the LDL-heparin complex, whereas factor Xa does not. Heparin, complexed with LDL, retains its enhancing effect on the rate of thrombin and plasmin inactivation by antithrombin III. LDL isolated from the plasma of persons with different pathological conditions did not alter the rate of thrombin inactivation by antithrombin III either in the absence or in the presence of heparin. Heparin seems to maintain its biological functions when it is in a complex with LDL.

Nephelometric determination of plasminogen and plasmin inhibitors in human plasma using fibrin suspension as a substrate

A nephelometric method is described for determination of plasminogen and two types of plasmin inhibitors in human plasma having different affinity toward plasmin. This method is based on the kinetic analysis of effects of whole plasma and plasmin inhibitor fraction obtained from plasma on the activity of exogenously added plasminogen which was determined by measuring the decrease of light scattering of fibrin suspension. With this method we have determined the activity of plasminogen and two types of inhibitors in the plasma of normal subjects and patients with high fibrinogen degradation product values. They include patients with various malignant tumors with DIC, chronic renal failure, sepsis, vascular diseases, and liver cirrhosis with hepatoma.

Aromatic amidines: comparison of their ability to block respiratory syncytial virus induced cell fusion and to inhibit plasmin, urokinase, thrombin, and trypsin

Two series of amidine derivatives consisting of a total of 24 compounds were examined for a correlation between their blocking effect on respiratory syncytial virus induced cell fusion and their inhibitory activity against selected trypsin-like protease. Although no correlation was evident between the two activities, several potentially important discoveries were made. A highly selective inhibitor of plasmin over thrombin (compound 10) was obtained, and a potent new blocker of virus-induced cell fusion (compound 22) was identified.

Plasminogen activator activity and plasmin inhibition in nerves

Histochemical studies of the distribution of fibrinolytic activity in the vagus and sciatic nerves of rat, guinea pig, and rabbit showed large areas of diffuse lysis related to the fascicles of the nerve. Foci of lysis were also located in the perineurium, in the peripheral epineurium, and particularly in the epineurium between the fascicles of the nerve. The fibrinolytic activity was caused by a plasminogen activator. The activity was highest in the rat, lowest in the rabbit and intermediate in the guinea pig. Plasmin inhibitors were located histochemically by the fibrin slide 'sandwich' technique. In all three species plasmin inhibition was most pronounced in relation to the nerve fascicles, with the highest degree of inhibition in the guinea pig and less in the rat and rabbit. The discrete localization of plasminogen activator and plasmin inhibitor might be of importance in the control of fibrin deposition and tissue repair following nerve injury or in inflammatory demyelinating diseases.

The interaction of heparin with human plasmin

1. The interaction of heparin with human plasmin was investigated measuring plasmin activity and enzyme inactivation in the presence of heparin. Hydrolysis of synthetic substrates (H-D-Val-Leu-Lys-pNA, H-D-Val-Phe-Lys-pNA and H-D-Pro-Phe-Lys-pNA) by plasmin was enhanced by heparin through an increase in kcat values. 2. This effect was the consequence of a change of Vmax since Km values were not altered in the presence of heparin. The polysaccharide also enhanced the rate of enzyme inactivation using TLCK as an active site blocking reagent. 3. Furthermore, heparin increased the heat sensitivity of plasmin, when synthetic substrate H-D-Val-Leu-Lys-pNA was used but it did not affect enzyme activity towards N-benzoyl-L-arginine-ethylester substrate. 4. The data show that microenvironmental conformation around the active center of plasmin is influenced by heparin.

Kinetics of the inhibition of plasmin in acidified human plasma

Acid-treated human plasma is a competitive inhibitor of the hydrolysis of D-Val-Leu-Lys-Nan (S-2251) by plasmin. The rate of hydrolysis is decreased to 50% by 750 fold diluted acidified normal plasma and by 60 fold diluted acidified alpha 2-antiplasmin depleted plasma (alpha 2-antiplasmin concentration less than 2%). These findings suggest that alpha 2-antiplasmin is a contributary but not the main competitive inhibitor of acidified plasma. This interpretation is supported by the finding that alpha 2-antiplasmin depleted plasma reconstituted with purified alpha 2-antiplasmin inhibits the hydrolysis of S-2251 by plasmin at a 125 fold dilution following acidification and by the finding that in a purified system acid inactivated alpha 2-antiplasmin inhibits the hydrolysis of S-2251 by plasmin with a Ki of 25 nM. Thus, besides alpha 2-antiplasmin, other plasma proteins which are at least in part eliminated by the removal of alpha 2-antiplasmin from plasma by immunoadsorption appear to be competitive inhibitors for plasmin in acidified plasma. It is suggested that several competitive inhibitors for plasmin are present and/or generated in acidified plasma and that these inhibitors may at least in part be responsible for the variability in the results of measurements of plasminogen and/or plasmin in plasma following acidification.

Proteolytic activation of influenza WSN virus in cultured cells is performed by homologous plasma enzymes

The effect of chick embryo allantoic fluid, porcine plasma or canine plasma on virus progeny was studied in cultured chicken, porcine and canine cells infected with influenza WSN virus. Cells incubated either without plasma or with heterologous plasma produced virions which had uncleaved haemagglutinin and low infectivity. Cells incubated with homologous plasma produced highly infectious virions with cleaved haemagglutinin. Little increase of progeny virus infectivity was observed in canine cell-porcine plasma and porcine cell-canine plasma host systems. The addition of protease inhibitors to culture containing homologous plasma, in particular epsilon-amino-n-caproic acid (an inhibitor of plasminogen activation), suppressed cleavage of haemagglutinin, and virions which had uncleaved haemagglutinin and low infectivity were produced by the cells. It therefore follows that haemagglutinin cleavage and activation of influenza WSN virus infectivity in cultured cells is most efficiently performed by homologous plasma proteolytic enzyme(s). The mechanism of selective plasma-mediated influenza virus proteolytic activation in homologous cells is discussed.

Pumpkin seed inhibitor of human factor XIIa (activated Hageman factor) and bovine trypsin

A strong inhibitor of human Hageman factor fragment (HFf, beta-factor XIIa) and bovine trypsin was isolated from pumpkin (Cucurbita maxima) seed extracts by acetone fractionation, by chromatography on columns of diethyl-aminoethylcellulose and carboxylmethyl-Sephadex C-25, and by Sephadex G-50 gel filtration. Pumpkin seed Hageman factor inhibitor (PHFI) is unusual in its lack of inhibition of several other serine proteinases tested--human plasma, human urinary, and porcine pancreatic kallikreins, human alpha-thrombin, and bovine alpha-chymotrypsin. Human plasmin and bovine factor Xa are only weakly inhibited. PHFI also inhibits the HFf-dependent activation of plasma prekallikrein and clotting of plasma. Other properties of PHFI are a pI of 8.3, 29 amino acid residues, amino-terminal arginine, carboxyl-terminal glycine, 3 cystine residues, undetectable sulfhydryl groups and carbohydrate, and arginine at the reactive site. The minimum molecular weight of PHFI is 3268 by amino acid analysis. PHFI may be the smallest protein inhibitor of trypsin known.

Mouse plasma trypsin inhibitors: inhibitory spectrum of contrapsin and alpha-1-antitrypsin

We have studied the effects of murine alpha-1-antitrypsin and contrapsin, a new trypsin inhibitor (Takahara, H. and Sinohara, H. (1982) J. Biol. Chem. 257, in press), on several serine proteases participating in blood clotting, fibrinolysis, kinin generation, and complement activation. Bovine plasmin and human plasma kallikrein were inactivated by contrapsin but not by alpha-1-antitrypsin, whereas bovine alpha-thrombin and porcine pancreas kallikrein were inhibited by alpha-1-antitrypsin but not by contrapsin. Heparin protected thrombin from inactivation by alpha-1-antitrypsin. Both inhibitors had virtually no effects on canine C1 esterase.

Purification and properties of a progesterone-induced plasmin/trypsin inhibitor from uterine secretions of pigs and its immunocytochemical localization in the pregnant uterus

The porcine uterus secretes a group of basic, low molecular weight protease inhibitors under the influence of progesterone, but not estrogen. One of these inhibitors (Mr approximately 14,500) which inhibits trypsin, plasmin, and chymotrypsin, but not other proteases tested, has been purified 10- to 15-fold from uterine secretions of pseudopregnant pigs using Sephadex G-100 chromatography, CM-cellulose ion exchange chromatography, and Sephadex G-50 or Bio-Gel P-10 chromatography. The inhibitor which is relatively heat- and pH-stable forms a 1:1 molar complex with trypsin which is not dissociated in sodium dodecyl sulfate except by boiling. Chymotrypsin appears to bind at the same site on the inhibitor as trypsin. The inhibitor is high in half-cysteine residues and basic amino acids, and appears not to be a glycoprotein. Antiserum has been raised against the purified inhibitor in rabbits and used to test its distribution in pigs using the immunoperoxidase-staining technique on tissue sections. The inhibitor is associated only with the glandular and surface epithelium of the uterus. Endometrial explants from pseudopregnant animals, cultured in presence of L-[3H]leucine, release the inhibitor in radioactive form indicating that it is a uterine product. The antiserum against the inhibitor cross-reacts with at least three other, basic, low molecular weights plasmin/trypsin inhibitors in porcine uterine secretions, suggesting that a family of isoinhibitors exists which may constitute up to 15% of the protein in porcine uterine secretions. The inhibitor(s) appears to coat and to be taken up by the trophoectoderm cells of the elongating blastocyst during pregnancy. It is suggested that the inhibitors may serve to protect the uterus from proteases released by the porcine trophoblast or to prevent degradation of essential macromolecules, such as uteroferrin, which have to be taken up by the conceptus.

Placental protein 5 is related to blood coagulation and fibrinolytic systems

Previous studies have shown that placental protein 5 (PP5) forms complexes with heparin. In order to further elucidate the biological role of PP5 we studied the effect of plasmin and thrombin on the immunoreactivity of PP5, and the possible functional antiplasmin and antithrombin effects of purified PP5. Varying concentrations of plasmin and thrombin were added to pregnancy plasma, and the PP5 levels, measured by radioimmunoassay, were found to be elevated by 558% (plasmin and 48-87% (thrombin). Incubation of radiolabeled PP5 with plasmin resulted in the formation of radioactive fragments with smaller molecular weights. Functional studies using a chromogenic substrate confirmed that purified PP5 has an antiplasmin activity. An average increase of 15% was observed in the antiplasmin activity when 200 ng purified PP5 was added to 150 microliters of pregnancy serum. Thus, there are certain similarities between PP5 and antihrombin III. Both form complexes with heparin and have antiplasmin properties, and both were found to be heat labile. But, functional studies utilizing a chromogenic substrate failed to demonstrate any antithrombin III-like activity in the purified PP5 preparation that had antiplasmin activity. Our results show that the function of PP5 is related to the blood coagulation and fibrinolytic systems, at least through its inhibitory action on plasmin.

The dexamethasone-induced inhibitor of fibrinolytic activity in hepatoma cells. A cellular product which specifically inhibits plasminogen activation

Dexamethasone induces an inhibitor of plasminogen-dependent fibrinolysis in rat hepatoma (HTC) cells. The specificity of the inhibitor for urokinase and plasmin was investigated using both fibrinolytic and esterolytic assays. Urokinase, but not plasmin, was inhibited by serum-free conditioned medium from cells incubated with 0.1 microM dexamethasone. The specificity of the inhibitor for plasminogen activator was demonstrated directly by the inhibition of the urokinase-catalyzed activation of 125I-plasminogen to 125I-plasmin. The inhibitory activity was stable to pH 3 for 2 h at 37 degrees C, a condition which inactivated fibrinolytic inhibitors in serum, suggesting a cellular origin for the inhibitor. Further evidence for the cellular origin was the constant daily production of inhibitor throughout a 4-day incubation with dexamethasone in serum-free medium. SF HTC-H1 cells, selected for their ability to grow in serum-free medium (Thompson, E. B., Anderson, C. U., and Lippman, M. E. (1975) J. Cell Physiol. 86, 403-412), were grown for 76 days (at least 30 generations) in the presence or absence of serum; dexamethasone induced equivalent amounts of inhibitory activity in cells which had been grown under both conditions. We conclude that the dexamethasone-induced inhibitor from HTC cells is a cellular product which is specific for the inhibition of plasminogen activation and which differs from other reported fibrinolytic inhibitors.

[Synthetic inhibitors of serine proteinases. Part 26: Inhibition of trypsin, plasmin and thrombin by amides of N alpha-arylsulfonylated 2-amino-4-(4-amidino-phenyl) butyric acid and 2-amino-5-amidinophenyl valeric acids (author's transl)]

Among the derivatives of the N alpha-arylsulfonylated omega-amidinophenyl-alpha-aminoalkyl carboxylic acids, the primary amides of N alpha-arylsulfonylated 2-amino-4-(4-amidinophenyl) butyric acid proved to be compounds with strong antiplasmin and antitrypsin activity, they exert, however, only slight inhibitory effect on thrombin. So far, no benzamidine derivatives with strong inhibitory effects on plasmin but with weak antithrombin activity have been known. The secondary amides of the N alpha-arylsulfonylated 2-amino-4-(4-amidinophenyl)butyric acid possess slight inhibitory effects, the corresponding derivatives of 2-amino-5-amidinophenyl valeric acids, however, are potent inhibitors of thrombin.

Acetylcholine receptor: effects of proteolysis on receptor metabolism

Previous studies (Miskin, R., T. G. Easton, and E. Reich, 1970, Cell. 15:1301-1312) have shown that sarcoma virus transformation and tumor promoters reduced the cell surface concentration of acetylcholine receptors (AChR) in differentiating chick embryo myogenic cultures. Both of these agents also induced high rates of plasminogen activator (PA) synthesis in myogenic cultures (Miskin, R., T. G. Easton, A. Maelicke, and E. Reich, 1978, Cell. 15:1287-1300), and the present work was performed to establish whether proteolysis might significantly affect receptor metabolism. Proteolysis in myogenic cultures was modulated by one or more of the following: stimulation of PA synthesis, direct addition of plasmin, removal of plasminogen, or addition of plasmin inhibitors. The results were: (a) When the rates of proteolysis were raised either by addition of plasmin or by stimulating PA synthesis in the presence of plasminogen, both the steady-state concentration and the half-life of surface AChR decreased, but the rate of receptor synthesis was unaffected. (b) The magnitude of these effects, and their dependence on added plasminogen, indicated that proteolysis initiated by plasminogen activation could account almost entirely for the reduction in receptor half-life produced by sarcoma virus transformation and phorbol ester. (c) The rate of receptor synthesis, which is also reduced by viral transformation and tumor promoters, was not modified by proteolysis; hence plasmin action may be responsible for a large part, but not all of the change in surface receptor under these conditions. (d) The plasmin catalysed changes in receptor parameters appear to occur in response to modified membrane metabolism resulting from proteolysis of surface components other than AChR itself.

GAGs-potentiated inhibition of thrombin, factor Xa and plasmin in plasma and in a purified system containing antithrombin III - correlation with total charge density

The ability of heparin and related glycosaminoglycans (GAGs) to accelerate the inhibition of thrombin, factor Xa and plasmin in plasma and in a purified system containing antithrombin III (At III) was studied using chromogenic peptide substrate assays. There was good correlation between the charge density of the mucopolysaccharides and the activities investigated. While the difference between potentiation of the antithrombin activity by GAGs in plasma and in the purified system was slight, the inhibition of factor Xa in plasma was more pronounced than in the presence of purified At III, indicating the mechanisms for GAGs-potentiated inhibition of thrombin and factor Xa are not identical. For the antiplasmin activity, there was a good correlation between the chemical structure and biological activity only in the pure system, confirming that the antithrombin-GAG complex plays a very limited role in the inactivation of plasmin in plasma.

Kinetic analysis of the heparin-enhanced plasmin--antithrombin III reaction. Apparent catalytic role of heparin

Inactivation of plasmin by a 3-4-fold molar excess of antithrombin III follows pseudo-first-order kinetics and the apparent rate constants are proportional to the concentration of the inhibitor. Heparin accelerates the inactivation reaction without changing its pseudo-first-order character, and the apparent rate constants are also proportional to the concentration of the polysaccharide. Heparin results in a minimum 20-fold rate enhancement of the reaction between plasmin and antithrombin III when the concentrations of heparin and plasmin are approx. 0.5mum and 1mum respectively. Heparin at a molar concentration well below that of plasmin still accelerates the reaction: one molecule of the polysaccharide is able to facilitate the inactivation of about 100 molecules of plasmin. Heparin must bind to plasmin to accelerate the plasmin-antithrombin III reaction, since the modification of four to five lysine residues of the enzyme inhibits the rate-enhancement effect of heparin and the dissociation of heparin-plasmin complex decreases the inactivation rate of plasmin. Increasing the concentration of antithrombin III, at a constant amount of heparin, results in increase of the inactivation rate. By contrast, the effect of increasing the amount of plasmin in the presence of constant amount of heparin and antithrombin III is such that higher plasmin-to-heparin ratios are associated with lower rates of inactivation. It seems, therefore, that to obtain ;optimal' conditions for fast enzyme inactivation, the amount of heparin should be matched to plasmin rather than to antithrombin III. Arrhenius plots of the plasmin-antithrombin III reaction are linear both in the absence and presence of heparin, at concentrations of 1 or 2mug/ml, over a range of 26K. Under these experimental conditions, heparin increases activation entropy. The findings show that heparin seems to fulfil some criteria that are characteristic for biological catalysis: binding, reaction-rate enhancement (increasing activation entropy), recycling of heparin (effectiveness of non-stoichiometric amounts of the polysaccharide) and specificity.

New synthetic inhibitors of C1r, C1 esterase, thrombin, plasmin, kallikrein and trypsin

p-Guanidinobenzoate derivates were prepared and their inhibitory effects on trypsin, plasmin, pancreatic kallikrein, plasma kallikrein, thrombin, C1r and C1 esterase were examined. Among the various inhibitors tested, 6'-amidino-2-naphthyl-4-guanidinobenzoate dihydrochloride, 4-(beta-amidinoethenyl)phenyl-4-guanidinobenzoate dimethanesulfonate and 4-amidino-2-benzoylphenyl-4-guanidinobenzoate dimethanesulfonate were the most effective inhibitors of trypsin, plasmin, pancreatic kallikrein. plasma kallikrein and thrombin and they strongly inhibited the esterolytic activities of C1r and C1 esterase, and then strongly inhibited complement-mediated hemolysis.

Kinetics of plasmin inhibition in the presence of a synthetic tripeptide substrate. The reaction with pancreatic trypsin inhibitor and two forms of alpha 2-plasmin inhibitor

The progressive inhibition of plasmin by pancreatic trypsin inhibitor and by alpha 2-plasmin inhibitor in the presence of D-valyl-L-leucyl-L-lysine 4-nitroanilide was investigated. The kinetics with plasmin were compared with those with miniplasmin. The kinetic properties of two functionally different forms of alpha 2-plasmin inhibitor described by Clemmensen [(1979) in The Physiological Inhibitors of Coagulation and Fibrinolysis (Collen. D., Wiman, B & Verstraete, M., eds.), pp 131-136, Elsevier, Amsterdam] were characterized. The two forms differ in their plasminogen-binding capability, and this difference can account for a difference in secondary site interaction suggested from the kinetics. The binding of inhibitor to miniplasmin is a simple pseudo-first-order reaction with both pancreatic trypsin inhibitor and the two alpha 2-plasmin inhibitor forms. Such simple kinetics are also observed for the reaction between plasmin and the non-plasminogen-binding form of alpha 2-plasmin inhibitor. More complicated kinetics are obtained for the reaction between plasmin and the alpha 2-plasmin inhibitor form that binds to plasminogen. With both forms of the alpha 2-plasmin inhibitor, a complex stable to acetic acid/urea and gel electrophoresis is present and fully developed 15 s after initiation of the reaction with plasmin.

Secondary-site binding of Glu-plasmin, Lys-plasmin and miniplasmin to fibrin

Active-site-inhibited plasmin was prepared by inhibition with d-valyl-l-phenylalanyl-l-lysylchloromethane or by bovine pancreatic trypsin inhibitor (Kunitz inhibitor). Active-site-inhibited Glu-plasmin binds far more strongly to fibrin than Glu-plasminogen [native human plasminogen with N-terminal glutamic acid (residues 1-790)]. This binding is decreased by alpha(2)-plasmin inhibitor and tranexamic acid, and is, in the latter case, related to saturation of a strong lysine-binding site. In contrast, alpha(2)-plasmin inhibitor and tranexamic acid have only weak effects on the binding of Glu-plasminogen to fibrin. This demonstrates that its strong lysine-binding site is of minor importance to its binding to fibrin. Active-site-inhibited Lys-plasmin and Lys-plasminogen (Glu-plasminogen lacking the N-terminal residues Glu(1)-Lys(76), Glu(1)-Arg(67) or Glu(1)-Lys(77))display binding to fibrin similar to that of active-site inhibited Glu-plasmin. In addition, alpha(2)-plasmin inhibitor or tranexamic acid similarly decrease their binding to fibrin. Glu-plasminogen and active-site-inhibited Glu-plasmin have the same gross conformation, and conversion into their respective Lys- forms produces a similar marked change in conformation [Violand, Sodetz & Castellino (1975) Arch. Biochem. Biophys.170, 300-305]. Our results indicate that this change is not essential to the degree of binding to fibrin or to the effect of alpha(2)-plasmin inhibitor and tranexamic acid on this binding. The conversion of miniplasminogen (Glu-plasminogen lacking the N-terminal residues Glu(1)-Val(441)) into active-site-inhibited miniplasmin makes no difference to the degree of binding to fibrin, which is similarly decreased by the addition of tranexamic acid and unaffected by alpha(2)-plasmin inhibitor. Active-site-inhibited Glu-plasmin, Lys-plasmin and miniplasmin have lower fibrin-binding values in a plasma system than in a purified system. Results with miniplasmin(ogen) indicate that plasma proteins other than alpha(2)-plasmin inhibitor and histidine-rich glycoprotein decrease the binding of plasmin(ogen) to fibrin.

[Synthetic inhibitors of serine proteinases. Part 25: Inhibition of trypsin, plasmin and thrombin by amides of N alpha-substituted amidinophenylalanines and 3-amidinophenyl-3-aminopropionic acids (author's transl)]

Amides of N alpha-substituted 3-amidinophenylalanine are potent inhibitors of the serine proteinases trypsin, plasmin and thrombin. They belong to the most potent inhibitors of these enzymes of the benzamidine type. In contrast, amides of 4-amidinophenylalanine possess weak inhibitory activity towards trypsin and plasmin. The cyclic amides of this group, however, are potent thrombin inhibitors. These derivatives are the first benzamidines with specific antithrombin activity. The isomeric compounds of 3-amidinophenyl-3-aminopropionic acids possess weak inhibitory effects on trypsin, plasmin and thrombin.