Biological activities of leupeptins

Separation of cathepsin D-like proteinase and acid thiol proteinase of squid mantle muscle

When the proteinases of the squid mantle muscle were extracted in the presence of dithiothreitol (DTT), the acid proteinase activity increased, indicating that the squid mantle muscle contains a considerable amount of the acid thiol proteinase. The crude extract hydrolyzed neither alpha-N-benzoyl-D,L-arginine-p-nitroanilide (BAPA) nor azocasein, thus refuting the presence of cathepsins B and L in the mantle muscle. The cathepsin D-like proteinase and the acid thiol proteinase were separated by Sephadex A-50 column chromatography. Each of the above partially purified proteinases was able to degrade carp actomyosin at pH 2.5 and 5.0, respectively.

The slow, tight-binding inhibition of cathepsin B by leupeptin. A hysteretic effect

Leupeptin was found to be a slow, tight-binding inhibitor of cathepsin B from human spleen and rabbit liver. During the enzyme-catalyzed reaction in the presence of inhibitor a concentration-dependent transient state, lasting several minutes, preceded the attainment of the steady state and was characterized by a concave upward or a concave downward lag phase depending on whether the enzyme had been preincubated with the inhibitor or not, respectively. From the pre-steady-state phase of the curves both k on and k off for the formation of the enzyme-inhibitor complex could be calculated. Ki, as the ratio k off/k on, was in good agreement with the inhibition constant obtained using a steady-state treatment. k on was 1.8 X 10(5) M-1 s-1 and 2.0 X 10(5) M-1 s-1 for the human and rabbit enzyme, respectively and the slowness of the binding process fitted into the general concept of enzyme hysteresis. The activation of the essential cysteine residue of cathepsin B by dithiothreitol was also a very slow process characterized by a second-order rate constant of 4.1 M-1 s-1. The kinetic features of leupeptin binding allow the prediction of the possible efficiency of this inhibitor on cathepsin B in vivo. It is shown that in order for leupeptin to be a physiologically significant inhibitor of cathepsin B, its concentration at the target site must exceed 10 microM, at least. This contrasts with the predictions drawn from the value of Ki (approximately 5 nM), which would suggest an effective inhibition of the enzyme already at a concentration of 0.05 microM.

Antiproteinase chemotherapy of acute experimental pancreatitis using the low molecular weight oligopeptide aldehyde leupeptin

Continuous intravenous infusion of the low molecular weight trypsin inhibitor leupeptin prolonged the survival of rats with acute haemorrhagic pancreatitis (p less than 0.001) compared with controls receiving saline alone. Rats receiving high dose intravenous Trasylol (aprotinin) survived no longer than saline-only controls. Combination therapy of leupeptin with Trasylol conferred no additional benefit over animals treated with leupeptin alone. The nature of the infusion was selected blind after the induction of pancreatitis and survival was quantified by recording of body temperature. These preliminary results suggest that sterically favourable molecules which can complete the inhibiton of alpha 2-macroglobulin bound proteinases should contribute to the effective specific chemotherapy of the disease.

Effects of adriamycin on heart and skeletal muscle chromatin

Interactions between adriamycin (ADM) and chromatin from heart and skeletal muscle from 15 day-old chicken embryos were investigated. Adriamycin interacts with the DNA of chromatin and this interaction is modified by the chromatin proteins. One of the effects of this interaction is an increase in the melting temperature (Tm) of the DNA, where adriamycin is observed to increase the Tm of heart chromatin to a greater extent than skeletal muscle chromatin. Adriamycin also inhibits in vitro DNA and RNA synthesis in isolated chromatin and nuclei. This inhibition is observed to be greater in heart muscle. Inhibition of transcription in the myocardium could be a major cause of adriamycin-induced cardiomyopathy.

Therapeutic trial with protease inhibitor (leupeptin) in chicken muscular dystrophy. A histologic and histochemical study

For the purpose of observing the therapeutic benefit of protease inhibitors for progressive muscular dystrophy, a large quantity of doses of leupeptin of 10 mg/kg/day and 50 mg/kg/day were administered i.p. to male chickens afflicted with hereditary muscular dystrophy (line 413) for 4 months starting on the 7th day ex ovo. No clinical improvement was identified in physical ability as a result of the examination by flip test, and creatine kinase (CK) values. The number of necrotic fibers in the pectoralis superficialis (PS) muscle which is known to be preferentially damaged in dystrophic chicken, did not decrease significantly in the birds treated with 10 mg leupeptin/kg/day (number of necrotic fibers; 47.7/mm2) and 50 mg/kg/day (46.4/mm2) as compared to that of the untreated ones (43.2/mm2). A morphometric analysis of fiber diameter distribution also showed no statistical difference between the treated and untreated birds. In the second group, 10 mg leupeptin/kg and a combination of leupeptin and bestatin of 10 mg/kg each were injected directly into the left lower half of the PS muscle three times a week for 4 months. Necrotic fibers were still present in the injected site, remote area of the left upper PS muscle treated with leupeptin (52.7/mm2), leupeptin and bestatin (52.2/mm2), and contralateral right upper PS muscle (41.6 and 53.5/mm2, respectively). The number of necrotic fibers in treated muscles was again not significantly different from that in untreated dystrophic ones (39.6/mm2). In fiber diameter analysis, no statistical difference was recognized between the treated and untreated dystrophic muscles.

Synthesis of leupeptins and inhibition of proteinases. I. Inhibition of acrosin and trypsin

A series of leupeptin analogs R-L-leucyl-L-leucyl-L-argininal with variable N-terminal substituents has been synthesized using N alpha-tert-butyl-oxycarbonyl-NG-benzyloxycarbonyl-L-arginine-delta-lactam as the starting material. The modified leupeptins proved to be strong competitive inhibitors of the endoprotease acrosin from mammalian spermatozoa. Inhibition constants were found in the range of 4.7 X 10(-7)M (R = H) to 9.7 X 10(-9)M (R = tert-butyloxycarbonyl). N alpha-tert-butyloxycarbonyl leupeptin represents the strongest acrosin inhibitor synthesized so far. Two of the leupeptin derivatives (R = trifluoroacetyl, R = tert-butyloxycarbonyl) were more effective than the natural leupeptins from microbial sources (Ki = 5.9 X 10(-8)M). The potential use of synthetic leupeptins as antienzymatic contraceptives is discussed.

A sepharose derivative coupled with a leupeptin-like peptide aldehyde, glycylglycyl-L-argininal, and its use as an affinity adsorbent for trypsin

A Sepharose derivative containing a peptide aldehyde, glycylglycyl-L-argininal, the structure of which resembles that of leupeptin was prepared. It was a strong affinity adsorbent for trypsin (EC 3.4.21.4). Bovine trypsin showed higher affinity for this adsorbent at the optimum pH of catalysis (8.2) than at lower pH (5.0). This observation was in good agreement with the pH dependence of the interaction of leupeptin and trypsin (Kuramochi, H., Nakata, H. and Ishii, S. (1979) J. Biochem. 86, 1403-1410). Streptomyces griseus trypsin was also adsorbed while trypsinogen, alpha-chymotrypsin and TLCK-trypsin were not adsorbed. Though anhydrotrypsin, in which Ser-183 is converted to dehydroalanine, was not adsorbed, carbamoylmethylated (His-46) trypsin was adsorbed. Ser-183 proved to be essential for the binding. This adsorbent can also be used as a good tool to study the mechanism of action of leupeptin.

Spectrophotometric assay, solubilization and purification of brain 2':3'-cyclic nucleotide 3'-phosphodiesterase

1. A spectrophotometric assay of 2':3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) based on the use of an acid-base indicator and a buffer having identical pKa values is described. The assay is simple and rapid; it was particularly convenient for monitoring the enzyme activity at various stages of purification. 2. Several proteinases were examined for their ability to solubilize 2':3'-cyclic nucleotide 3'-phosphodiesterase from delipidated brain white matter. Trypsin (EC 3.4.21.4) and elastase (EC 3.4.21.11) appeared to be more effective than the other proteinases examined. Trypsin, however, caused inactivation; elastase was therefore chosen to solubilize 2':3'-cyclic nucleotide 3'-phosphodiesterase. When a partially purified preparation of 2':3'-cyclic nucleotide 3'-phosphodiesterase was treated with elastase, 2':3'-cyclic nucleotide 3'-phosphodiesterase was solubilized nearly quantitatively. Elastatinal, a specific inhibitor of elastase, specifically inhibited the solubilization with elastase. 3. 2':3'-cyclic nucleotide 3'-phosphodiesterase was purified from bovine brain white matter by: (i) delipidation; (ii) solubilization with hexadecyltrimethylammonium bromide; (iii) gel chromatography on Sepharose; (iv) ethanol precipitation and resolubilization by digestion with elastase; (v) chromatography on DEAE-Sephadex; (vi) affinity chromatography on 8-(6-aminohexyl)amino-2'-AMP-Sepharose. 4. The purified enzyme migrated as a single protein band on polyacrylamide-gel electrophoresis at pH 4.3 and on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; the estimated mol.wt. in the latter electrophoresis was 27000-31000. Gel filtration of the purified enzyme through Sephadex G-150 indicated a mol.wt. of 31000. Therefore the purified enzyme is a monomer protein with a mol.wt. of approx. 30000.

Human cathepsin B. Application of the substrate N-benzyloxycarbonyl-L-arginyl-L-arginine 2-naphthylamide to a study of the inhibition by leupeptin

1. The kinetic parameters Kcat. and Km were determined for the hydrolysis of some arginine naphthylamides by human cathepsin B. 2. A new and efficient synthesis of Z-Arg-Arg-NNap (benzyloxycarbonyl-L-arginyl-L-arginine 2-naphthylamide) was developed. 3. Z-Arg-Arg-NNap was a specific and sensitive substrate for cathepsin B, and was used for kinetic studies. 4. Values of kcat. were maximal in the pH range 5.4--6.2, and depended on a single ionizing group of pKa 4.4. 5. Leupeptin was a purely competitive inhibitor of human cathepsin B. 6. The effect of pH on the apparent inhibitor constant, Ki (app.), was determined. Ki (app.) was pH-independent in the range pH 4.3--6.0, with the mean value 7 x 10(-9) M.

Suppression and acceleration of experimental amyloidosis in mouse model

Leupeptins, protease inhibitors, suppress the appearance of experimental amyloidosis in CBA mice induced by the injections with complete Freund's adjuvant. This substance, however, should be administered continuously from 1 week prior to amyloid induction to the end of the experiment. On the other hand, Trypan blue, inhibitors of lysosomal enzymes, accelerates experimental amyloidosis in the mouse model above-mentioned. Trypan blue is effective when given either prior to or at the same time of the initiation of amyloid induction. Organic Germanium has not been confirmed to be a potent suppressor of experimental murine amyloidosis but the experimental group administered this substance continuously from 1 week prior to the induction shows a rather low incidence of amyloidosis, and the average number of amyloidotic organs per affected mouse is about half of that of the control group. The suppression and acceleration of experimental murine amyloidosis presented here are a useful tool for investigating the pathogenesis of amyloidosis.

Inhibition of immune complex-mediated activation of complement. Effects of agents modulating activation of, and the activated C1 complex

Several known chemical compounds were shown to selectively inhibit the interaction between immune aggregates and C1q, the activation of C1r-C1s complex by immune aggregate-bound C1q, and the esterolytic activity of the activated C1s, C1s. These reactions are relevant to the functions of the first complement component, C1, and its activation induced by immune complexes. The effects of these inhibitors on tissue injury mediated by immune complex-induced complement activation, such as immune hemolysis, passive cutaneous anaphylaxis, and experimental glomerulonephritis were examined. The results suggest an approximate correlation between the activity shown on the molecular level and that obtained in vivo. One such compound, suramin, was shown to be an effective inhibitor of PCA and the proteinuria manifestation of EGN while not affecting antibody fixation to tissue or histamine-mediated skin reaction. These results suggest that effective suppression of the initial steps of complement activation may be of value of controlling immune complex-mediated tissue injuries in disease.

The effects of intravenously administered chlorophyll-A on naturally occurring serum protease inhibitors in rabbits

Effects of intravenously administered protease inhibitors on naturally occurring serum inhibitors were investigated in rabbits. Water-dispersed chlorophyll-a, trasylol and leupeptin were tested as exogenous protease inhibitors in the experiments. From the results of experiments, it was concluded that: 1) Pretreatment with chlorophyll-a infusion into rabbits, most effectively prevented the rapid consumption of naturally occurring serum protease inhibitors after successive trypsin infusion, and the duration of its action was observed longest when compared with other exogenous inhibitors, such as trasylol or leupeptin. 2) Final therapeutic effects of these exogenous protease inhibitors seem to have depended upon the disappearing way of the administered inhibitors from the blood in certain period of time, as well as upon biochemical potency of their inhibiting activity.

The lipoxygenase of reticulocytes. Purification, characterization and biological dynamics of the lipoxygenase; its identity with the respiratory inhibitors of the reticulocyte

A lipoxygenase has been purified from rabbit reticulocyte-rich anaemic blood cells. It possesses a molecular weight of 78 000 and an isoelectric point of 5.5 and contains 5% neutral sugars and two iron atoms per enzyme molecule. The lipoxygenase has proved to be identical with the inhibitors of respiratory proteins described formerly. The actions of the lipoxygenase on linoleic acid, phospholipids, mitochondrial and erythrocyte membranes and electron transfer particles were studied. A special feature of the reticulocyte lipoxygenase is the suicidal character of its action on lipids. With electron transfer particles the reticulocyte lipoxygenase causes a loss of acid-labile sulfur which accompanies respiratory inhibition; the strong respiratory inhibition is not exerted by soybean lipoxygenase. The reticulocyte lipoxygenase acts preferably on mitochondrial membranes as compared with cell membranes of the erythrocyte; erythrocyte cytosol moderates the action on mitochondrial membranes. Furthermore, the lipoxygenase reaction can concomitantly and irreversibly inactivate sulfhydryl enzymes as demonstrated with muscle glyceraldehyde-3-phosphate dehydrogenase. The occurrence of the lipoxygenase here described is restricted to reticulocytes; very low amounts were observed in bone marrow and no lipoxygenase was detectable in normal blood. During the course of an experimental anaemia the lipoxygenase is produced owing to superinduction in large amounts, which may persist for a long time since they escape inactivation. Preliminary evidence was obtained for the occurrence of other lipoxygenases in tissues of lung, spleen, kidney and also epithelial tumours.

Protease inhibitors reduce the reverse passive Arthus reaction

Trasylol, ovomucoid, tranexamic acid and soybean inhibitor decrease the vascular permeability as measured by extravasation of 131I-albumin when injected with the antibody at induction of a reverse passive Arthus reaction in the rat skin. Trasylol given systemically also had a suppressive effect, similar to phenylbutazone. When the reaction was induced in the pleural cavity, both Trasylol and tranexamic acid reduced the influx of leucocytes.

Leupeptin, a protease inhibitor, decreases protein degradation in normal and diseased muscles

The protease inhibitor leupeptin decreases protein degradation in rat skeletal and cardiac muscle incubated in vitro, while protein synthesis remains unaltered. Leupeptin also lowers protein breakdown in denervated rat muscles and affected muscles from mice with hereditary muscular dystrophy. Leupeptin may thus be useful in retarding tissue atrophy. Since homogenates of leupeptin-treated muscles had decreased cathepsin B activity, this lysosomal protease may play a role in protein turnover in normal and diseased muscles.

Antiproteolytic aldehydes and ketones: substituent and secondary deuterium isotope effects on equilibrium addition of water and other nucleophiles

Equilibrium constants for hydration of ketones, in dilute D2O solution at 34 degrees C, observed by proton magnetic resonance under conditions of slow exchange, were acetone 0.002, chloroacetone 0.08, 1,3-dichloroacetone 4.17, bromoacetone 0.07, and 1,3-dibromoacetone (an inhibitor of papain) 1.85. Neither acetamidoacetone nor N,N-diacetylaminoacetone showed evidence of appreciable hydration in dilute aqueous solution, nor was any hydrate detectable in solutions of tosylglycine chloromethyl ketone. Substitution of acetaldehyde with acylamido substituents, as in several potent reversible inhibitors of papain, was found to enhance its equilibrium constant for covalent hydration by an order of magnitude; these inhibitors are about 90% hydrated in dilute aqueous solution, and their affinity for proteases may have been underestimated accordingly. The effects of deuterium substitution at C-1 of acetaldehyde, on equilibrium addition of oxygen and sulfur nucleophiles, are substantial and vary with the nature of the nucleophile. These isotope effects may be useful as a mean of distinguishing between alternative structures of complexes formed between enzymes and aldehydes.

Inhibition of protein degradation in isolated rat hepatocytes

1. Isolated parenchymal cells were prepared by collagenase perfusion of livers from fed rats that had been previously injected with [(3)H]leucine to label liver proteins. When these cells were incubated in a salts medium containing glucose, gelatin and EDTA, cellular integrity was maintained over a period of 6h. 2. Cells incubated in the presence of 2mm-leucine to minimize radioactive isotope reincorporation released [(3)H]leucine into the medium at a rate accounting for the degradation of 4.5% of the labelled cell protein per h. 3. Degradation of [(3)H]protein in these cells was inhibited by insulin and by certain amino acids, of which tryptophan and phenylalanine were the most effective. 4. Protein degradation was decreased by several proteinase inhibitors, particularly those that are known to inhibit lysosomal cathepsin B, and by inhibitors of cell-energy production. 5. Ammonia inhibited degradation, but only at concentrations above 1.8mm. Aliphatic analogues of ammonia were effective at lower concentrations than was ammonia. 6. High concentrations of ammonia inhibited degradation by 50%. The extent of this inhibition could not be increased further by the addition of the cathepsin B inhibitor leupeptin, which by itself inhibited degradation by approx. 30%. 7. The sensitivity of proteolysis in isolated hepatocytes to these various inhibitory agents is discussed in relation to their possible modes of action.

Aminopeptidase activities on the surface of mammalian cells

Activities of hydrolytic enzymes on the surface of monkey kidney, canine kidney, L. FM3A and various tumor cells were determined and compared with those in the cell homogenate. Although aminopeptidase (EC 3.4.11.-) activities were always detected on the surface membrane in mammalian cells, trypsin, chymotrypsin and elastase activities were not detected while slight glycosidase activity was detected in a suspension of cultured cells. The activities of alanine-, leucine-, methionine- and phenylalanine-aminopeptidases were rather high but aminopeptidase A, proline-, valine-, glycyl propline dipeptidyl-and glycyl propyl leucine-tripeptidyl-aminopeptidases showed relatively low activities. Aminopeptidase activity was also demonstrated in the isolated membrane fractions. The specific activities of enzymes in these membrane fractions were not significantly greater than in cell homogenate so it was concluded that these enzyme activities were rather loosely bound to the cell membrane. Further evidence for the localization of the aminopeptidase activities on the cell surface was obtained by using glass-bead-bound substrate and detecting the release of the terminal residues. When bestatin, a specific inhibitor against aminopeptidase B and leucine aminopeptidase, was included in the assay system for the enzyme activities on the cell surface, the enzymes were commonly inhibited in all types of cells.

Macrophage esterase: identification, purification and properties of a chymotrypsin-like esterase from lung that hydrolyses and transfers nonpolar amino acid esters

A chymotrypsin-like esterase was purified from beef lung. This lysosomal enzyme, not previously characterized, seemed to be composed of two or more forms with molecular weights of about 52 000. It hydrolysed N-benzoyl-DL-phenylalanine beta-naphthol ester at acid and neutral pH; it polymerized L-phenylalanine methyl ester(Phe-OMe) at neutral pH; and it transferred the Phe-residue from Phe-OMe to hydroxylamine at neutral pH. Phenylmethanesulfonyl fluoride, an inhibitor of hydrolytic enzymes with serine in their catalytic site, inhibited this enzyme, but pepstatin, the cathepsin D (EC 3.4.4.23) inhibitor, did not. Sulfhydryl reagents were not required for activity. Macrophages, especially pulmonary alveolar macrophages, were a rich source of this esterase, so it is likely that the enzyme purified from lung came from its macrophages. The esterase hydrolysed and transferred monoamino acid esters, especially those of the aromatic type. Cathepsin C, the dipeptidyl peptide hydrolase (EC 3.4.14.1), acted only on dipeptide esters and amides. Pancreatic chymotrypsin acted on both monoamino acid and dipeptide esters. The chymotrypsin-like esterase did not hydrolyse hemoglobin, casein, or plasma albumin. Thus its proteolytic activity, if present, must be limited to specific substrates, as yet unknown.

Fractionation of the rat liver enzymes that hydrolyze benzoyl-arginine-2-naphthylamide

1. The enzyme activity in the particulate fraction from rat liver that hydrolyzes alpha-N-benzoyl-DL-arginine-2-naphthylamide (Bz-Arg-NNap) has been separated into two approximately equal components by chromatography on DEAE-cellulose. One component (peak II) is completely retained by the column at low ionic strength while the other component (peak I) passes through. 2. In contrast to the enzyme in peak I, the enzyme in peak II is extremely sensitive to inhibition by leupeptin, it will hydrolyze carbobenzoxy-alanylarginylarginyl-4-methoxy-2-naphthylamine, and it will inactivate aldolase. 3. There appears to be also a minor high molecular weight component of the alpha-N-benzoyl-DL-arginyl-2-naphthylamine-hydrolyzing activity that is retained by the DEAE-cellulose but which has properties similar to those of the peak I enzyme.

Enzymatic catalysis and transition-state theory

The application of transition-state theory to enzymatic catalysis provides an approach to understanding enzymatic catalysis in terms of the factors that determine the strength of binding of ligands to proteins. The prediction that the transition state should bind to the enzyme much more tightly than the substrate is supported by the experimental results with stable analogs of transition states. Transition-state analogs have great potential for use in understanding enzymatic catalysis and in inhibiting enzymes. Because of their potency and specificity as enzyme inhibitors, some of them may become very useful chemotherapeutic agents.