Protease-inhibitory activities of leupeptin analogues

Thirty analogues of leupeptin were synthesized and examined for their inhibitory activities against trypsin, papain, plasmin, kallikrein, thrombin and urokinase in vitro. Benzoyl- and alpha-naphthalenesulfonyl-L-leucyl-L-argininal were 8 times more inhibitory to papain, benzyloxycarbonyl-L-pyroglutamyl-L-leucyl-L-argininal 10 times more to trypsin and plasmin, and DL-2-pipecolyl-L-leucyl-L-argininal 25 times more to kallikrein than leupeptin. Against urokinase, only L-pyroglutamyl-L-leucyl-L-argininal exhibited a potent inhibitory activity. alpha-Naphthalensulfonyl-, dansyl- and benzyloxycarbonyl-(2S,3R)-3-amino-2-hydroxy-4-phenylbutyryl-L-leucyl-L- argininal were inhibitory to thrombin.     

Comparative studies of nafamostat mesilate and various serine protease inhibitors in vitro

Inhibitory effects of nafamostat mesilate (nafamostat) on various enzymes were investigated, and they were compared with those of gabexate mesilate (gabexate), leupeptin, aprotinin and urinastatin in vitro. Nafamostat inhibited trypsin, plasmin, thrombin, pancreatic kallikrein, Clr and Cls more potently than gabexate and leupeptin. Gabexate and leupeptin did not inhibit pancreatic kallikrein and thrombin, respectively. Aprotinin inhibited trypsin, plasmin, pancreatic kallikrein and chymotrypsin. Urinastatin inhibited trypsin and chymotrypsin. Nafamostat inhibited the complement-mediated hemolysis in diluted serum more potently than gabexate and leupeptin, but aprotinin and urinastatin did not. Nafamostat, furthermore, inhibited the complement-mediated hemolysis in undiluted serum, but gabexate did not. Unlike aprotinin and urinastatin, nafamostat and gabexate inhibited alpha 2-macroglobulin bound trypsin as well as free trypsin to the same extent. The inhibitory effect of gabexate toward trypsin was reduced more markedly than that of nafamostat after incubation with plasma at 37 degrees C. These results show that nafamostat is more useful than other inhibitors such as gabexate, leupeptin, aprotinin and urinastatin.     

Survey of plant inhibitors of polymorphonuclear leukocyte elastase, pancreatic elastase, cathepsin G, cathepsin B, Hageman factor fragments, and other serine proteinases

Various flower bulbs and vegetable and legume seeds were tested for inhibitors of polymorphonuclear leukocyte elastase, pancreatic elastase, cathepsin G, cathepsin B, trypsin, alpha-chymotrypsin, Hageman factor fragments, plasma kallikrein, and plasmin. Calla bulbs contained a 33,000 dalton polymorphonuclear leukocyte elastase inhibitor and a 4,000 dalton cathepsin G inhibitor. Seeds of some members in the Cruciferae family, such as radish and broccoli, were found to contain one or more 2,500-4,000 dalton inhibitors which inhibited cathepsin G, trypsin, Hageman factor fragments, and plasmin, but not plasma kallikrein. These seeds also contained a 1,000 dalton cathepsin B inhibitor. The above inhibitors were probably polypeptides which inhibited proteinases by making an enzyme-inhibitor complex, with the exception of the cathepsin B inhibitor. These newly found inhibitors with their characteristic profiles of inhibition should be useful in biochemical and pathophysiological studies on granulocyte proteinases and enzymes of the coagulation and fibrinolytic pathways.     

Effect of invertebrate serine proteinase inhibitors on carrageenan-induced pleural exudation and bradykinin release

The carrageenan model of pleurisy is described as temporal plasma exudation (1-5 h) with extensive neutrophil infiltration and release of proteinases into the pleural cavity. The aim of this work was to study the effects of serine proteinase inhibitors on the inflammatory process induced by administration of carrageenan to the rat pleural cavity and on release of kinins in pleural exudate. Pleurisy was induced by injecting carrageenan and serine proteinase inhibitors simultaneously into the pleural cavity. The proteinase inhibitors used were: aprotinin, a plasma kallikrein inhibitor; recombinant leech derived tryptase inhibitor-2PL (LDTI-2PL), a plasmin inhibitor; Boophilus microplus trypsin inhibitors (BmTIs); trypsin; plasma kallikrein; plasmin and neutrophil elastase inhibitors; and a synthetic neutrophil elastase inhibitor (EIsynt). Administration of carrageenan with LDTI-2PL and BmTIs induced a marked increase in exudation (143% and 201%) and leukocyte migration (288% and 408%), respectively, when compared to the control group. Pleural exudate from LDTI-2PL and BmTIs plus carrageenan-treated rats showed a significant increase in plasma kallikrein-like activity, measured by chromogenic substrate hydrolysis. The specific inhibition of enzymatic activity with aprotinin confirmed that 50% of S2302 hydrolysis was produced by plasma kallikrein-like enzymes. Kinin release was increased by 97% and 103% in exudates from LDTI-2PL and BmTIs plus carrageenan-treated rats, respectively. Considering that the plasmin inhibitors LDTI-2PL and BmTIs increased exudation, leukocyte migration and bradykinin release, our results suggest an anti-inflammatory role for plasmin in the pleurisy model.     

Effects of netropsin and pentamidine amino analogues on the amidolytic activity of plasmin, trypsin and urokinase

Inhibitory effects of nine carbocyclic DNA minor groove binders on amidolytic activities of plasmin, trypsin and urokinase were examined. Some of the studied compounds affected plasmin or trypsin activity, but not urokinase activity. One of the pentamidine analogues (5) and two bis-netropsin like compounds (6, 8) were potent inhibitors of plasmin (IC50 equals 90 and 100 microM), whereas an analogue of netropsin (2) was trypsin inhibitor (IC50 = 100 microM).     

A new strategy for the development of highly potent and selective plasmin inhibitors

A new structure-based strategy for the design of potent and selective plasmin inhibitors was developed. These compounds could be prepared by cyclizations between the P3 and P2 amino acid residues of substrate-analogue inhibitors using metathesis or a copper-catalyzed azide alkyne cycloaddition in combination with standard peptide couplings. The most potent bis-triazole derivative 10 inhibits plasmin and plasma kallikrein with K(i) of 0.77 and 2.4 nM, respectively, whereas it has poor activity against the related trypsin-like serine proteases thrombin, factor Xa, or activated protein C. Modeling experiments revealed that inhibitor 10 adopts a compact and rigid structure that fits well into the relatively open active site of plasmin and plasma kallikrein, while it is rejected from sterically demanding residues present in loops of the other enzymes. These results from modeling confirm the selectivity profile found for inhibitor 10 in enzyme kinetic studies. Such compounds might be useful lead structures for the development of new antifibrinolytic drugs for use in cardiac surgery with cardiopulmonary bypass or organ transplantations to reduce bleeding complications.     

Synthesis and kinetic evaluation of peptide alpha-keto-beta-aldehyde-based inhibitors of trypsin-like serine proteases

New, synthetic peptide analogues bearing a C-terminal basic alpha-keto-beta-aldehyde moiety were prepared as novel inhibitors of the trypsin-like serine proteases. The compounds, Ac-Leu-Leu-Arg-COCHO, Ac-Arg-Gln-Arg-COCHO and Boc-Val-Leu-Lys-COCHO were evaluated kinetically against trypsin and three other trypsin-like serine proteases, tryptase, plasmin and thrombin, all of which are implicated as mediators of important disease processes. Results illustrate that alpha-keto-beta-aldehydes are potent inhibitors, with similar potency to comparable peptide aldehydes, and intriguingly, appearto act, in some instances, by a novel mechanism of action. Ac-Leu-Leu-Arg-COCHO, an analogue of the natural product leupeptin, is a potent, tight-binding inhibitor of trypsin (Ki(final) = 1.9 microM), plasmin (Ki(final) = 4.9 microM) and tryptase (Ki(final) = 1.2 microM) and an irreversible inactivator of thrombin (k2nd 4,500 M(-1).min(-1)). Boc-Val-Leu-Lys-COCHO was found to be a tight-binding inhibitor of its target protease plasmin (Ki(final) = 3.1 microM) and was inactive against thrombin. Ac-Arg-Gln-Arg-COCHO was a slow-binding inhibitor of tryptase (Ki(final) = 1.6 microM) and also irreversibly inactivated trypsin (k2nd = 8,920 M(-1) min(-1)). Peptides or peptidomimetics with a C-terminal basic alpha-keto-beta-aldehyde function thus provide a useful new molecular template for the development of new therapeutic agents against a wide range of disorders, such as coagulopathies and asthma, which may be mediated by the aberrant activity of trypsin-like serine proteases.     

Effect of [ethyl p-(6-guanidinohexanoyloxy)benzoate] methanesulfonate (FOY) on kinin formation and fibrinolysis activity]

Inibitory effects of [Ethyl p-(6-guanidinohexanoyloxy)benzoate] methanesulfonate (FOY) on kinin formation (in vitro and in vivo) and the fibrinolytic activity (in vivo) were examined and compared with otherinhibitors. Inhibitory effect on kinin forming activity (in vitro) of various enzymes was measured in the guinea pig ileum. FOY and Trasylol inhibited the kinin forming activities of trypsin, pancreas kallikrein and plasma kallikrein. Soybean trypsin inhibitor inhibited kinin like substance was formed in the perfusate when the rat's paw was heated at 46 degrees C. FOY and T-asylol added to the perfusion fluid produced a potent inhibition of the formation of bradykinin-like substance. When administered i.v., FOY and Trasylol did not inhibit the formation of bradykinin-like substance. In the dog, activation of plasmin in the circulatory blood and increase of hemorrhagic tendency were caused by the i.v. administration of human serum plus streptokinase. Such responses were inhibited with a previous i.v. infusion of FOY and t-AMCHA. From the above findings, it may be concluded that FOY has inhibitory effects on kinin formation and fibrinolytic activity.     

Purification and preliminary characterization of a plasma kallikrein inhibitor isolated from sea hares Aplysia dactylomela Rang, 1828.

An inhibitor active against pancreatic trypsin was found in the crude extract from the sea hares Aplysia dactylomelaRang, 1828. A stronger inhibitory activity against human plasma kallikrein was detectable after treating this extract at 60 degrees C, for 30 min. The plasma kallikrein inhibitor (AdKI) purification was achieved by acetone fractionation (80%) v/v, ion-exchange chromatography on Mono Q column and gel filtration chromatography on Superdex 75 column (FPLC system). By the latter a molecular mass of 2900 Da was estimated. The purified inhibitor strongly inhibits human plasma kallikrein with a K(i) value of 2.2 x 10(-10)M, while human plasmin and pancreatic trypsin were inhibited with K(i) values of 1.8 x 10(-9) and 4.7 x 10(-9)M, respectively. Chymotrypsin, pancreatic elastase, pancreatic kallikrein and thrombin are not inhibited. The effect of AdKI on plasma kallikrein was confirmed by the prolongation of activated partial thromboplastin time, using a clotting time assay. The inhibitor did not affect prothrombin time or thrombin time. AdKi is a more specific inhibitor than other serine proteinase inhibitors from marine invertebrates.     

Kinetic characterization of factor Xa binding using a quenched fluorescent substrate based on the reactive site of factor Xa inhibitor from Bauhinia ungulata seeds

The specific Kunitz Bauhinia ungulata factor Xa inhibitor (BuXI) and the Bauhinia variegata trypsin inhibitor (BvTI) blocked the activity of trypsin, chymotrypsin, plasmin, plasma kallikrein and factor XIIa, and factor Xa inhibition was achieved only by BuXI (K(i) 14 nM). BuXI and BvTI are highly homologous (70%). The major differences are the methionine residues at BuXI reactive site, which are involved in the inhibition, since the oxidized protein no longer inhibits factor Xa but maintains the trypsin inhibition. Quenched fluorescent substrates based on the reactive site sequence of the inhibitors were synthesized and the kinetic parameters of the hydrolysis were determined using factor Xa and trypsin. The catalytic efficiency k(cat)/K(m) 4.3 x 10(7) M(-1)sec(>-1) for Abz-VMIAALPRTMFIQ-EDDnp (lead peptide) hydrolysis by factor Xa was 10(4)-fold higher than that of Boc-Ile-Glu-Gly-Arg-AMC, widely used as factor Xa substrate. Lengthening of the substrate changed its susceptibility to factor Xa hydrolysis. Both methionine residues in the substrate influence the binding to factor Xa. Serine replacement of threonine (P(1)') decreases the catalytic efficiency by four orders of magnitude. Factor Xa did not hydrolyze the substrate containing the reactive site sequence of BvTI, that inhibits trypsin inhibitor but not factor Xa. Abz-VMIAALPRTMFIQ-EDDnp prolonged both the prothrombin time and the activated partial thromboplastin time, and the other modified substrates used in this experiment altered blood-clotting assays.     

The inhibition of the enzymic activity of blood coagulation and fibrinolytic serine proteases by a new leupeptin-like inhibitor, and its structural analogues, isolated from Streptomyces griseus

A group of leupeptin analogues was found in Streptomyces griseus strain 254, isolated from a soil sample from Fujian Province, China. The inhibitors excreted in the culture filtrate were purified by adsorption on macroporous resin, followed by sequential ion exchange chromatography on DEAE-52 cellulose, CM-32 cellulose and affinity chromatography with immobilized trypsin. The preparation thus obtained was further purified by preparative HPLC. Several major components were found and characterized, which possessed different inhibitory properties toward trypsin. Based upon amino acid and mass spectrophotometric analysis, these peptides were placed in four major structural categories, viz., R-Val-Val-argininal, R-Leu-Leu-argininal, R-Ile-Ile-argininal and R-Thr-Thr-argininal, this latter component representing a newly identified leupeptin analogue. The structural variability of the R-group was partly responsible for the multiplicity of the peaks obtained with HPLC. All peptides displayed varying degrees of inhibitory activity toward proteases involved in blood coagulation and fibrinolysis, including plasmin, factor Xa, activated protein C and thrombin. Among these peptide inhibitors, the molecule containing threonine showed the strongest inhibitory activity.     

Bauhinia bauhinioides plasma kallikrein inhibitor: interaction with synthetic peptides and fluorogenic peptide substrates related to the reactive site sequence

A serine proteinase inhibitor was purified from Bauhinia bauhinioides seeds after extraction with 0.15M NaCl by ion-exchange column chromatography on DEAE-Sephadex, gel filtration on Superose 12 column, Mono Q chromatography or alternatively by affinity chromatography on trypsin- Sepharose. The inhibitor is a single polypeptide chain with molecular mass 20 kDa by gel filtration on Superose 12, but was resolved into two peaks by ion - exchange chromatography on Mono Q (FPLC system). The main eluted peak inhibits trypsin (Ki = 0.6 nM), plasma kallikrein (Ki = 0.35 nM), plasmin (Ki = 33.1 nM), and weakly chymotrypsin (Ki = 2,700 nM), being the most effective plasma kallikrein inhibitor isolated from Bauhinia seeds. Therefore, it was denominated Bauhinia bauhinioides kallikrein inhibitor (BbKI). Activity is thermolabile and on trypsin inhibition optimum pH is 8.0. BbKI displays high homology to other plant Kunitz inhibitors, except for the absence of disulfide bridges, and the only cysteine residue is at the C-terminal position (residue 154) characterizes a distinct member of the Kunitz family. The affinity of the inhibitor to trypsin was confirmed by adsorption to trypsin-Sepharose resin and by isolation of the trypsin-inhibitor complex by gel filtration. Peptides with variations around the reactive site of BbKI (GLPVRFESPLRINIIKESY) were synthesized containing a quenched fluorogenic group. Trypsin but not plasma kallikrein substrates, these peptides strongly inhibited plasma kallikrein.     

Vascular permeability factors (PF/Nat and PF/Dil)--their relationship to Hageman factor and the kallikrein-kinin system.

Permeability factor/native (PF/Nat) and permeability factor/dilute (PF/Dil), the factors in diluted plasma exposed to glass which increase vascular permeability of small blood vessels, were examined for their ability to hydrolyze p-tosylarginine methyl ester and to activate prekallikrein. The direct arginine esterase activity of diluted plasma gave a pattern of activity and inhibition similar to that previously described for PF/Nat, while the ability of diluted plasma to activate prekallikrein was similar to that for PF/Dil. Electrophoretic analyses on polyacrylamide gel of these dilutions showed that the direct arginine esterase activity was distributed through the gel with a major peak of activity in the globulin region. PF/Dil, on the other hand, like active Hageman factor (HF) preparations, had two major peaks of activity located in the globulin and albumin regions. Studies with plasma deficient in HF, PTA (Factor XI), prekallikrein (Fletcher factor) and plasmin suggested that HF, prekallikrein and possibly PTA, but not plasmin, are required for maximal generation of these activities in plasma. Plasma deficient in C'l esterase inhibitor generates far more direct arginine esterase activity and PF/Dil than normal plasma. A number of inhibitors of HF, of plasmin and of trypsin were examined for their ability to inhibit the activation of HF during dilution, the active HF found after dilution and plasma kallikrein. The present data would suggest that active HF and/or its fragments and PF/Dil are identical enzymes. The direct arginine esterase activity generated by glass contact in these experiments may be kallikrein bound to α-2-macroglobulin.     

Subunits of human plasma kininase II generated by plasma kallikrein.

Partially purified human plasma kininase II was incubated with proteolytic enzymes such as plasma kallikrein, prekallikrein activator, plasmin, thrombin and trypsin. Digestion of plasma kininase II by plasma kallikrein generated 180,000 (I) and 95,000 (II) mol. wt subunits while plasmin, thrombin and trypsin inactivated plasma kininase II. These subunits have two activities just as plasma kininase has: they hydrolyze bradykinin, and they convert angiotensin I into angiotensin II. K_m values of the two subunits for bradykinin were 0.17 × 10^?6 M, indicating that this value was identical with plasma kininase II. V_max values of the two subunits for bradykinin were higher than that of plasma kininase II. The bradykininase activities of the two subunits were significantly inhibited by inhibitors such as HgCl₂, ethylenediamine tetraacetic acid. p-chloromercuriphenyl sulfonic acid, SQ 20881(BPF9a), soy bean trypsin inhibitor and Trasylol. The behaviour of the two subunits towards these above inhibitors was also identical with plasma kininase II. A 180,000 mol. wt kininase was partially purified from human plasma. The kininase had bradykinin-inactivating and angiotensin I-converting activities. Its K_m value and the behaviour towards the inhibitors described above were the same as the subunit I.     

Expression and purification of natural N-terminal recombinant bovine pancreatic trypsin inhibitor from Pichia pastoris

Bovine pancreatic trypsin inhibitor (BPTI) is a natural non-specific serine protease inhibitor and possesses the ability to inhibit trypsin, chymotrypsin, plasmin and plasma kallikrein. The expression of BPTI in Escherichia coli and other systems has been reported. However, the preparation of recombinant BPTI (rBPTI) with correct N-terminus in Pichia pastoris has not been successful. A previous study showed that the preBPTI with the prepro leader sequence of alpha mating factor (AMF) was not processed into natural BPTI in P. pastoris. Now, we introduce a new method to prepare rBPTI, which carries a natural N-terminal amino acid residue, Arg-Pro-Asp, in P. pastoris using human serum albumin signal peptide corresponding to the pre sequence. The concentration of rBPTI in an 80 l fermentor reached 900 mg/l. We also explored a rapid and simple purification protocol for rBPTI and the purity of rBPTI reached 95-98% as evaluated by SDS-PAGE analysis. The sequencing results showed that the sequence of N-terminal 15 amino acids of rBPTI was consistent with that of natural BPTI. The inhibitory activity of rBPTI against trypsin was the same as natural BPTI and its K(i) was 2.6+/-0.1 x 10(-9). The therapeutic effect of rBPTI on acute pancreatitis was identified in rats.     

4-Heterocyclohexanone-based inhibitors of the serine protease plasmin.

Three inhibitors that are based upon a 4-heterocyclohexanone nucleus were synthesized and evaluated for activity against the serine protease plasmin. Inhibitors of plasmin have potential as cancer chemotherapeutic agents that act by blocking both angiogenesis and metastasis. Inhibitor 1 has moderate activity against plasmin but shows good selectivity for this enzyme compared to other serine proteases including trypsin, thrombin, and kallikrein. Inhibitor 2 shows both good activity and selectivity for plasmin. Inhibitor 3, which does not incorporate an aminohexyl group that can interact with the S1 subsite, has poor activity. These results, along with previous work, demonstrate that the 4-heterocyclohexanone nucleus can effectively serve as the basis for designing inhibitors of both serine and cysteine proteases.     

Guanidinophenyl-substituted enol lactones as selective, mechanism-based inhibitors of trypsin-like serine proteases.

We have synthesized four guanidinophenyl-substituted protio enol and iodo enol lactones (3-(4-guanidinophenyl)-6-methylidenetetrahydro-2-pyranone (1), 3-(4-guanidinophenyl)-6-(E)-(iodomethylidene)tetrahydro-2-pyran one (2), 4-(4-guanidinophenyl)-6-methylidenetetrahydro-2-pyranone+ ++ (3), and 4-(4-guanidinophenyl)-6-(E)-(iodomethylidene)tetrahydro-2-pyran one (4)) and tested them for inhibitory activity against some trypsin-like enzymes, namely trypsin, urokinase, tissue plasminogen activator (t-PA), plasmin, and thrombin, as well as alpha-chymotrypsin and human neutrophil elastase (HNE). The beta-aryl-substituted protio lactone 3 was a potent alternate substrate inhibitor of trypsin and urokinase. The alpha-aryl-substituted iodo lactone 2 was a permanent inactivator of urokinase, plasmin, t-PA, thrombin, and alpha-chymotrypsin, exhibiting a relatively high specificity for the former two enzymes. In general, these compounds showed a preference for inactivating trypsin-like enzymes over alpha-chymotrypsin and HNE. Also, within the class of trypsin-like enzymes, there was generally good selectivity of inhibition.     

Distribution of proteinase inhibitors in snake venoms

Potent proteinase inhibitors, which inactivate bovine pancreatic trypsin, α-chymotrypsin, bovine plasma kallikrein and plasmin, were found in several snake venoms. The content of the inhibitor was highest in Vipera russelli venom. Proteinase inhibitors of the same type were demonstrated also in the venoms of five snakes of the Elapidae family; Hemachatus haemachatus (Ringhals cobra), Dendroaspis angusticeps (Green mamba), Dendroaspis polylepis (Black mamba), Naja nivea (Cape cobra) and Naja haje (Egyptian cobra). No proteinase inhibitors were demonstrated in several Crotalidae and Hydrophiidae venoms. Toxic polypeptides such as α-bungarotoxin, cytotoxin I and II (Naja naja venom) and cardiotoxin (Naja naja atra venom) did not show any inhibitory action on typical mammalian proteinases including trypsin, α-chymotrypsin, plasmin and kallikrein.     

Potent,small-molecule inhibitors of human mast cell tryptase. Antiasthmatic action of a dipeptide-based transition-state analogue containing a benzothiazole ketone

Inhibitors of human mast cell tryptase (EC 3.4.21.59) have therapeutic potential for treating allergic or inflammatory disorders. We have investigated transition-state mimetics possessing a heterocycle-activated ketone group and identified in particular benzothiazole ketone (2S)-6 (RWJ-56423) as a potent, reversible, low-molecular-weight tryptase inhibitor with a K(i) value of 10 nM. A single-crystal X-ray analysis of the sulfate salt of (2S)-6 confirmed the stereochemistry. Analogues 12 and 15-17 are also potent tryptase inhibitors. Although RWJ-56423 potently inhibits trypsin (K(i) = 8.1 nM), it is selective vs other serine proteases, such as kallikrein, plasmin, and thrombin. We obtained an X-ray structure of (2S)-6 complexed with bovine trypsin (1.9-A resolution), which depicts inter alia a hemiketal involving Ser-189, and hydrogen bonds with His-57 and Gln-192. Aerosol administration of 6 (2R,2S; RWJ-58643) to allergic sheep effectively antagonized antigen-induced asthmatic responses, with 70-75% blockade of the early response and complete ablation of the late response and airway hyperresponsiveness.     

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.