Biological activities of leupeptins

Cleavage of the epidermal growth factor receptor by a membrane-bound leupeptin-sensitive protease active in nonionic detergent lysates of senescent but not young human diploid fibroblasts

Numerous studies suggest that epidermal growth factor (EGF) signaling is impaired in nonproliferating senescent human diploid fibroblasts downstream of receptor binding. One possible explanation for these results is that senescent cells possess unique enzymatic activities capable of regulating functional levels of the EGF receptor. To test that hypothesis, nonionic detergent lysates of young and senescent cells were compared for proteolytic activity directed towards the EGF receptor, and a protease that cleaves the 170 kDa EGF receptor was identified in lysates from senescent but not young cells. Although studies presented here were carried out with WI-38 cells, our data indicate that other senescent fibroblasts possess a similar activity. The degradation product immunoprecipitated by a monoclonal antibody specific for an EGF receptor exocytosolic epitope had an approximate molecular weight of 100,000. This product was also detected following cell surface labeling with 125I, and by cross-linking 125I-EGF to intact cells with disuccinimidyl suberate. The proteolytic activity in senescent cell lysates was specifically inhibited by leupeptin and did not require divalent cations; it was also inactivated by aprotic solvents such as dimethylsulfoxide (DMSO) or ethylene carbonate. Interestingly, this protease was not active during ligand-induced intracellular processing of the EGF receptor, suggesting that it does not normally function in endocytic or lysosomal compartments. The susceptibility of the protease to inactivation by cell surface trypsinization is consistent with a plasma membrane localization. Since EGF receptor cleavage is not observed unless senescent cells are solubilized with nonionic detergents, it seems likely that the protease is confined to specialized regions of the plasma membrane. Whether or not the EGF receptor is a physiologic target for this protease is unclear. Its expression at the cell surface is nevertheless significant, since it suggests there are mechanisms for regulating membrane-bound proteins, or biologically active peptides in the extracellular space, in senescent cells that are either absent or inactive in young cells.

[14C]Methylamine accumulation in cultured human skin fibroblasts--a biochemical test for lysosomal storage and lysosomal diseases

Incorporation of the lysosomotropic amine [14C]methylamine by fibroblasts cultured from patients with lysosomal storage diseases and from controls was used to estimate the size of the lysosomal compartment. All cell lines from patients with infantile and juvenile forms of mucopolysaccharidoses, mucolipidoses and oligosacharidoses showed markedly increased radioactivity compared with the normal range of controls. In cells from patients with sphingolipidoses and adult forms of storage diseases, however, methylamine accumulation was not significantly increased. Experimentally induced lysosomal storage by enzyme inhibitors (leupeptin, suramin) also caused increased methylamine accumulation. When the lysosomal pH was determined with fluorescein isothiocyanate-dextran, it was in the range of normal controls (pH 4.7-5.0) in patients cells. Thus, [14C]methylamine accumulation should depend on the volume rather than differences in acidity of the lysosomal compartment and be a measure of its eventual pathological enlargement. We conclude that the determination of [14C]methylamine accumulation in fibroblasts provides a valuable tool in the screening for a variety of lysosomal storage disorders.

Synthetic inhibitors of elastase

For more than two decades investigators around the world, in both academic and industrial institutions, have been developing inhibitors of human neutrophil elastase. A number of very elegant and insightful strategies have been reported. In the case of reversible peptidic inhibitors, this has resulted in the identification of some extremely potent compounds with dissociation constants in the 10(-11) M range. This is quite an accomplishment considering that these low molecular-weight inhibitors are only tri- and tetrapeptides. In the case of the heterocyclic-based inhibitors, the challenge of balancing the heterocycle's inherent reactivity and aqueous stability with the stability of the enzyme-inhibitor adduct has been meet by either using a latent, reactive functionality which is only activated within the enzyme, or by incorporating features which selectively obstruct deacylation but have little effect on the enzyme acylation step. The underlying goal of this research has been the identification of agents to treat diseases associated with HNE. Several animal models have been developed for evaluating the in vivo activity of elastase inhibitors, and compounds have been shown to be effective in all of these models by the intravenous, intratrachael or oral routes of administration. However, only a very small percentage of compounds have possessed all the necessary properties, including lack of toxicity, for progression into the clinic. The peptidyl TFMK ICI 200,880 (25-12) has many of the desired characteristics of a drug to treat the diseases associated with HNE: chemical stability, in vitro and in vivo activity, a long duration of action, and adequate metabolic stability. Currently ICI 200,880 is the only low molecular-weight HNE inhibitor known to be undergoing clinical trials, and may be the compound which finally demonstrates the clinical utility of a synthetic HNE inhibitor.

Rapid and convenient purification of tonin from rat submandibular gland. Comparison of tonin and tissue kallikrein in their interactions with inhibitors

Tonin was isolated from rat submandibular glands by a very convenient procedure consisting of sequential anion-exchange, hydrophobic interaction and gel filtration chromatographies. The method is superior to earlier purifications as it consists of fewer stages, resulting in a much higher recovery (41%) of tonin. The final preparation was seen to be pure on SDS gel electrophoresis (M(r) 32,800) and on gel isoelectric focusing (pI 6.15). The stability of tonin and its interaction with various inhibitors were investigated, and compared with the corresponding behavior of rat tissue kallikrein.

Trypsin and affinity chromatography

Affinity adsorbents for trypsin which were prepared by immobilizing product-type ligands, that is, peptides having C-terminal arginine, proved to be effective not only for preparative purposes but also for basic research on molecular recognition. The properties of the binding site of trypsin were revealed by chromatographic experiments. Quantitative analysis based on the theory of frontal affinity chromatography proved to be extremely effective. As an extension of the product-type ligands, peptide argininals were also used and information on the mechanism of action of these inhibitors was obtained. Anhydrotrypsin, which lost the hydroxyl group of Ser183, was found to gain increased binding ability for product-type compounds. This inactivated enzyme was also used as an immobilized ligand and the unique affinity adsorbent thus prepared proved to be extremely effective for the separation of peptides and recombinant proteins based on their C-terminal structures. High-performance affinity chromatography of trypsin and related enzymes using a polymer-based support was also developed.

Separation, purification and N-terminal sequence analysis of a novel leupeptin-sensitive serine endopeptidase present in chemically induced rat mammary tumour

Leupeptin is a small peptide microbially derived inhibitor of certain proteolytic enzymes. Using N-alpha-benzoyl-DL-arginine 4-nitroanilide as substrate, we found a novel leupeptin-sensitive proteolytic enzyme in N-methyl-N-nitrosourea(MNU)-induced rat mammary adenocarcinoma. This enzyme was apparently different from urokinase-type plasminogen activator or cathepsin B and was present in mammary tumour at levels at least 20 times higher than those in normal mammary tissue. This enzyme was separated and purified from crude extracts of MNU-induced mammary adenocarcinoma approx. 1900-fold with 34% yield. It was a trypsin-like serine endopeptidase and had a pH optimum at 7.0. The native enzyme had an apparent M(r) of 180,000 and exhibited four isoelectric points ranging from 4.3 to 5.0. Electrophoresis of denatured enzyme, however, yielded, with reduction, a major band with an apparent M(r) of 37,500 and a minor band with an apparent M(r) of 35,500. The N-terminal 23 residues of the major band were Ile1-Val2-Gly3-Gly4-Gln5-Glu6-Ala7-+ ++Ser8-Gly9-Asn10-Lys11-Xaa12-Pro13- Val14- Gln15-Val16-Xaa17-Leu18-Xaa19-Val20- Trp21-Leu22-Pro23. These and other properties of this enzyme suggested that it most closely resembles rat skin tryptase, followed by rat peritoneal mast-cell tryptase and then by tryptases from other species. The rat, like human and mouse, may carry multiple tryptase genes, and this mammary-tumour enzyme may be an additional form of rat tryptase within a new serine-proteinase family.

Chymotrypsin-like and trypsin-like protease activities in the sea urchin (Hemicentrotus pulcherrimus) egg

Proteolytic activities in extracts of sea urchin eggs were examined using SDS (sodium dodecyl sulphate)-polyacrylamide gels. In the unfertilized eggs, proteases were detected as bands corresponding to the molecular weights of 40 kD and 26 kD on the gelatin gel, and 35 kD and 30 kD on the casein gel. Using various protease inhibitors, it was found that 40 kD, 30 kD, and 26 kD are chymotrypsin-like proteases and that 35 kD is a trypsin-like protease. The activity of the 40 kD chymotrypsin-like protease was found to be almost completely lost after insemination.

Intraventricular infusion of leupeptin decreases Bmax of the D2 receptor in the striatum of young rats

Intraventricular infusion of a thiol protease inhibitor, leupeptin, was previously shown to induce several morphological and immunochemical manifestations of normal and pathological aging in rat brain. The present study attempted to elucidate whether this treatment also perturbs another brain function which declines in aging, dopamine D2 receptor binding in striatum. Intraventricular infusion of leupeptin (0.6 mg per day) for two weeks caused a significant (about 20%) reduction in the binding maximum (Bmax) of dopamine D2 receptors (as examined by [3H] spiperone binding) in the striatum of young male Fischer-344 rats in comparison to (saline-infused) control rats. The apparent Kd values did not differ significantly between the control and leupeptin-treated rat groups. The results suggest that decreased protein turnover may be a factor in the decline in Bmax of D2 receptors during aging.

Characterization of Porphyromonas (bacteroides) gingivalis hemagglutinin as a protease

A hemagglutinin (HA) was purified to homogeneity from the membrane fraction of the oral bacterium Porphyromonas gingivalis. The HA possessed protease activity hydrolyzing proteins and arginine-containing synthetic substrates. The protease activity was inhibited by thiol-blocking reagents, and hence the HA can be characterized as a cystein protease. The HA functions as an attachment factor and its substrate-binding site is responsible for the attachment to an erythrocyte.

Soluble fibrin preparations inhibit the reaction of plasmin with alpha 2-macroglobulin. Comparison with alpha 2-antiplasmin and leupeptin

The kinetics of plasmin inhibition by alpha 2-antiplasmin (alpha 2AP), alpha 2-macroglobulin (alpha 2M) and leupeptin were studied in the presence of fibrin monomer (Fn) and CNBr fragments of fibrinogen (Fg-CNBr). Active plasmin was detected in continuous and discontinuous assays using the chromogenic substrate D-Val-L-Leu-L-Lys p-nitroanilide hydrochloride (S-2251). The two 'fibrin-like' preparations functioned as hyperbolic mixed-type inhibitors of S-2251 hydrolysis. The dissociation constants (KF) for the binding of plasmin to Fn and Fg-CNBr were 22 nM and 17 nM respectively. Fn and Fg-CNBr inhibited the reaction of plasmin with alpha 2AP: the extent of inhibition depended on the fibrin concentration. In the presence of 800 nM-Fn or 800 nM-Fg-CNBr, the experimental second-order rate constant (K"app.) was decreased from 2.4 x 10(7) M-1.s-1 to 1.2 x 10(6) and 5.3 x 10(5) M-1.s-1 respectively. The effect of Fn and Fg-CNBr on the rate of plasmin inhibition by alpha 2M was even greater. The k"app. value was decreased from 4.0 x 10(5) M-1.s-1 to 8.0 x 10(2) and 1.3 x 10(3) M-1.s-1 in the presence of 800 nM-Fn and -Fg-CNBr respectively. By contrast, the fibrin preparations caused only a small change in the rate of plasmin inhibition by leupeptin. The maximum change in k"app. was 3-fold. All plasmin inhibition curves were linear, suggesting that free and fibrin-bound forms of plasmin remained in equilibrium during the course of reaction with proteinase inhibitors. Fn and Fg-CNBr had no effect on the reaction of miniplasmin with S-2251, alpha 2AP or alpha 2M. When 125I-plasmin was incubated with Fg-CNBr and then allowed to react with a premixed solution of alpha 2AP and alpha 2M, the Fg-CNBr did not significantly change the percentage of plasmin bound to alpha 2AP. These experiments demonstrate that the reaction of plasmin with alpha 2M is inhibited by the non-covalent binding of plasmin to fibrin. We propose that plasmin bound to the surface of a clot is protected from inhibition by alpha 2M as well as by alpha 2AP.

Leupeptin causes an accumulation of lipofuscin-like substances in liver cells of young rats

Leupeptin, a thiol protease inhibitor, has previously been shown to cause a dense accumulation of substances resembling age pigment and called ceroid-lipofuscin, in brain cells of young rats. Thus far, however, attempts to produce age pigments in hepatocytes of normal young rats with protease inhibitor(s) have not been successful. The present study provides the first demonstration that leupeptin induces lipofuscin-like substances in normal young rat hepatocytes. Male Fischer-344 rats (age 4-6 weeks) were continuously infused with leupeptin or saline i.p. for 2 weeks by an osmotic minipump (dosage, 1-50 mg/100 g per day). Liver tissues were then examined by light, fluorescence and electron microscopy. Both hepatocytes and non-parenchymal cells of livers treated with leupeptin, but not saline, showed a dense accumulation of pigments which stained deeply with toluidine blue, were PAS-positive and were brightly autofluorescent. After UV excitation the pigments had an emission spectrum with a broad peak at 480-540 nm extending to 650 nm resembling the spectrum of age pigment from livers of normal aged rats. Electron microscopic examination revealed numerous lipofuscin-like deposits with heterogeneous morphology in the cytoplasm of both hepatocytes and non-parenchymal cells; lipid and myelin-like bodies were also present in hepatocytes. The results indicate that the perturbation of proteolytic activity in liver by leupeptin causes an accumulation of substances which by several criteria resemble lipofuscin. These results thus provide further support for the 'Protease Inhibitor Model of Lipofuscin Formation' as well as a potential experimental model for studying hepatocellular aging processes.

The protease inhibitor leupeptin induces several signs of aging in brain, retina and internal organs of young rats

The protease inhibitor leupeptin was administered to brain, retina and internal organs of young rats for up to two weeks in order to determine if specifically decreased proteolysis could cause symptoms of cellular aging in a variety of tissues. Electron microscopy showed that leupeptin induced the formation of dense substances with fine morphologies similar to and, in many cases, apparently identical with those of natural lipofuscin from aged tissues. Leupeptin also caused increased immunoreactivity to ubiquitin in cerebellar Purkinje cells and presumed Bergmann glia perikarya of brain tissue as well as in hepatocytes of liver tissue. Both of these effects were found in aged tissues as well. Finally, both leupeptin treatment and normal aging led to the onset of immunoreactivity in Purkinje cells to antibodies to the abnormal tau molecule of paired helical filaments from Alzheimer's disease brain. Together, these results indicate that inhibition of thiol (and possibly some serine) proteases by leupeptin is sufficient to cause obvious morphological manifestations of aging in several tissues, and are thus consistent with the hypothesis that lipofuscinogenesis as well as a build-up of ubiquilinated proteins with age is caused by decreased or defective proteolysis. These effects are likely secondary to the mechanism(s) interfering with proteolysis itself.

A novel leupeptin-sensitive serine endopeptidase present in normal and malignant rat mammary tissues

N-Methyl-N-nitrosourea (MNU)-induced rat mammary adenocarcinomas contain high levels of a novel leupeptin-sensitive serine endopeptidase. Its properties apparently differ from those of other similar endopeptidases reported to be present in various normal and malignant mammalian tissues. The same leupeptinsensitive serine endopeptidase was also detected in normal rat mammary tissues, but at levels approximately 20 times lower than those in MNU-induced mammary tumors. This enzyme, which is a trypsin-like serine endopeptidase, preferentially hydrolyzes various synthetic endopeptidase substrates at the carboxyl side of an arginyl residue. It has an apparent Mr of approximately 160,000 and a Stokes radius of 49 A, as determined by gel filtration. Its isoelectric points range from 4.5 to 4.8, and it has a pH optimum of approximately 7.0. The enzyme is stable from pH 4.0 to 7.0, but is extremely unstable above pH 7.0. Besides leupeptin, its activity is inhibited by antipain, aprotinin, N alpha-p-tosyl-L-lysine chloromethyl ketone and phenylmethylsulfonyl fluoride, but is not inhibited by soybean trypsin inhibitor. Many other potential inhibitors or activators such as 2-mercaptoethanol, p-hydroxymercuribenzoic acid and EDTA have no effect on its activity. The enzyme is adsorbed to p-aminobenzamidine agarose affinity beads at pH 6.5 and elutes at pH 4.0.

Morphological, physiological and biochemical alterations in livers of rodents induced by protease inhibitors: a comparison with old livers

A "Protease inhibitor model of aging" has been proposed primarily based on observations on brain tissues exposed to a thiol protease inhibitor, leupeptin (Ivy et al., 1984a). In order to validate this model in terms of a mechanism of cellular aging, as well as of lipofuscin formation in particular, attempts have been made to induce lipofuscin in hepatocytes in young rodent (rat and mouse) livers by continuous i.p. infusion of two different thiol protease inhibitors, leupeptin and E-64C. With doses of leupeptin higher than 1.0 mg/100g/day for 2 wks, a fine granular lipofuscin-like deposition with distinct yellowish-green fluorescence was induced in young rat hepatocytes. The deposition became greater in degree with increasing leupeptin doses. In Kupffer cells and other endothelial cells, fluorescent granules were also induced. In contrast to rat livers, lipofuscin-like pigments induced in hepatocytes in mice were much less, even with a higher dose (20 mg/100 g/day). E-64C also induced the accumulation of lipofuscin-like pigments at a dose of 5 mg/100 g/day, their characteristics being very similar to those induced by leupeptin, but the accumulation being smaller in degree. The fluorescence of leupeptin induced lipopigments was yellowish-green having a peak around 520 nm in emission profile, closely resembling that observed in old rat livers. The hepatobiliary transport functions such as biliary transport maximum (Tm) for sulfobromophthalain and the biliary recovery of iv injected ouabain which are known to decline with age tended to decline in young (6-wk-old) rats administered with leupeptin at a dose of 5 mg/100 g/day for 2 wks. On the other hand, dolichol concentration in leupeptin treated livers was not increased in comparison to control livers, whereas in old rat livers, the dolichol concentration was more than 2 times greater than in young livers. A clear-dose-dependent deposition of ceroid-lipofuscin induced in young rodent livers by protease inhibitors strongly suggests that the "Protease inhibitor model" is generally valid not only for the brain but for other tissues such as the liver, and for two different thiol protease inhibitors.

Possibility of Bacteroides gingivalis hemagglutinin possessing protease activity revealed by inhibition studies

Inhibition of hemagglutinin (HA) activity in a membrane fraction of Bacteroides gingivalis was examined using various compounds. Leupeptin and anti-pain inhibited the HA activity at nM order. This potency was lost when the aldehyde group of leupeptin was converted to an alcohol moiety. Irreversible protease inhibitors, tosyl-L-lysine chloromethyl ketone (TLCK), p-chloromercuribenzoate (PCMB), and N-ethylmaleimide (NEM) were also inhibitory. From the inhibition experiments, we speculate that the HA possesses protease activity and that the same site of the molecule participates in the erythrocyte binding and the substrate binding.

Inhibition of cathepsin B by peptidyl aldehydes and ketones: slow-binding behavior of a trifluoromethyl ketone

Inhibition of the cysteine proteinase cathepsin B by a series of N-benzyloxycarbonyl-L-phenylalanyl-L-alanine ketones and the analogous aldehyde has been investigated. Surprisingly, whereas the aldehyde was found to be almost as potent a competitive reversible inhibitor as the natural peptidyl aldehyde, leupeptin, the corresponding trifluoromethyl ketone showed comparatively weak (and slow-binding) reversible inhibition. Evaluation of competitive hydration and hemithioketal formation in a model system led to a structure-activity correlation spanning several orders of magnitude in both cathepsin B inhibition constants (Ki) and model system equilibrium data (KRSH,apparent).

Regulation of the production of a prolactin-like protein (MRP/PLF) in 3T3 cells and in the mouse placenta

Mitogen-regulated protein (MRP), a heterogeneously glycosylated mouse protein of Mr 34,000, is in the same protein family as prolactin, growth hormone, and placental lactogen. We show here that the level of translatable MRP mRNA is increased in response to fibroblast growth factor. Also, the amount of MRP secreted by 3T3 cells is modulated by the rate of degradation of newly synthesized MRP in the lysosomes. This is indicated by several results. First, agents that inhibit protein degradation by lysosomal proteases selectively increased by 2- to 6-fold the incorporation of [35S]methionine into MRP. These agents are ammonium chloride, the carboxylic ionophores, monensin and nigericin, and two thiol protease inhibitors, leupeptin and antipain. MRP that has already been secreted is not degraded by 3T3 cells. We examined the developmental appearance of MRP using immunofluorescence microscopy and found MRP localized in the mouse placenta between days 9 and 13 of development. The amount of MRP in the placenta drops suddenly after day 13. Whereas the appearance of MRP in the placenta follows the reported appearance of its mRNA, MRP disappears from the placenta more rapidly than its mRNA. On the basis of the results of our studies with cells in culture we propose that the production of MRP in the placenta is regulated similarly to prolactin. Thus we propose that the initial increase in MRP production in the placenta is due to pretranslational regulation by growth factors, and the later rapid decline is due to posttranslational regulation through degradation in the lysosomes.

Proteases of the nematode Caenorhabditis elegans

Crude homogenates of the soil nematode Caenorhabditis elegans exhibit strong proteolytic activity at acid pH. Several kinds of enzyme account for much of this activity: cathepsin D, a carboxyl protease which is inhibited by pepstatin and optimally active toward hemoglobin at pH 3; at least two isoelectrically distinct thiol proteases (cathepsins Ce1 and Ce2) which are inhibited by leupeptin and optimally active toward Z-Phe-Arg-7-amino-4-methylcoumarin amide at pH 5; and a thiol-independent leupeptin-insensitive protease (cathepsin Ce3) with optimal activity toward casein at pH 5.5. Cathepsin D is quantitatively most significant for digestion of macromolecular substrates in vitro, since proteolysis is inhibited greater than 95% by pepstatin. Cathepsin D and the leupeptin-sensitive proteases act synergistically, but the relative contribution of the leupeptin-sensitive proteases depends upon the protein substrate.

Relative deficiency of serine proteinase activities in spleens of aged mice

We examined the relation of hydrolytic enzymes in spleen to the aging process in mice over a period of 30 months. When the enzymatic activities were expressed as activities per milligrams protein, those of serine proteinases and dipeptidyl peptidase IV (Gly-Pro-AP) significantly decreased with age, whereas that of L-leucine aminopeptidase (Leu-AP) increased significantly. However, when expressed as total activities, the enzymatic activities in spleen generally tended to increase with age, except in the case of serine proteinases, because of the age-related increase in spleen weight. The results were taken to indicate that the activities of serine proteinases become relatively more deficient in the spleen as age increases. The results of a multivariate study maintained this peculiarity of serine proteinases in comparison with other enzymes. The relative deficiency of serine proteinases in spleen may be somehow related to immunodeficiency in aged animals, as judged from similar findings in animal models of systemic erythematodes.

An enzymatic mechanism for calcium current inactivation in dialysed Helix neurones

'Wash-out' and inactivation of the Ca current were examined in dialysed, voltage-clamped neurones of Helix aspersa under conditions that isolate the Ca current virtually free of other currents. EGTA or other internal Ca2+ chelators were routinely omitted from the dialysate. The time-dependent loss, or wash-out, of Ca current was slowed by addition to the dialysing solution of agents, such as dibutyryl adenosine 3'-5'-cyclic monophosphate (dibutyryl cyclic AMP), Mg adenosine 5'-triphosphate (ATP) and the catalytic subunit of cyclic-AMP-dependent protein kinase, that promote protein phosphorylation and by EGTA. However, neither the phosphorylation-promoting agents nor internal EGTA prevented wash-out entirely, nor did they significantly restore previously 'washed-out' current. With phosphorylating agents in the dialysing solution, the irreversible development of wash-out was greatly reduced by introduction of leupeptin, an inhibitor of protease activity. Thus, the irreversible component of wash-out appears to result from a Ca-dependent proteolytic process. In the presence of leupeptin alone, Ca current amplitude continued to decline: however, the current could be largely or fully restored with addition of catalytic subunit, dibutyryl cyclic AMP, and Mg ATP to the dialysing solution. Thus, inhibition of proteolysis revealed a reversible component of wash-out that appears to result from dephosphorylation. During perfusion with leupeptin, Mg ATP, dibutyryl cyclic AMP and catalytic subunit the Ca current remained stable for up to several hours without addition of internal Ca2+ buffer. The rate of inactivation of the current that occurs during a depolarizing step showed only a very gradual decline during this time. Under these conditions, perfusion with calcineurin, a Ca-calmodulin-dependent phosphatase, caused a significant increase in the rate of Ca current inactivation. This inactivation was virtually eliminated by introduction of EGTA or by replacement of external Ca2+ with Ba2+, which is consistent with the ion dependency for calmodulin-dependent activation of calcineurin. When ATP in the dialysate was replaced with ATP-gamma-S (adenosine 5'-O-(thiotriphosphate], an analogue that donates a thiophosphate group resistant to hydrolysis, the rate of inactivation slowed. Since Ca-dependent inactivation during step depolarizations is enhanced by conditions that promote dephosphorylation, and Ca current wash-out is slowed by conditions that promote phosphorylation, inactivation and reversible wash-out appear to be related.(ABSTRACT TRUNCATED AT 400 WORDS)

Assay of plasma leupeptin using the reversible binding of leupeptin to bovine pancreatic trypsin

A competitive binding radioassay for leupeptin has been developed utilizing the reversible binding of leupeptin to bovine pancreatic trypsin. An ethanol precipitation step was introduced to separate trypsin-bound leupeptin from its free form. Advantages of this method are simplicity of the procedure and avoidance of the preparation of antiserum. The possible metabolites of leupeptin exhibit no significant inhibitory effect on leupeptin-trypsin binding in this system. This method was applied to the determination of plasma leupeptin levels in dogs after oral administration of the peptide.

Beneficial effect of chymostatin on dystrophic mice

We studied the effect of chymostatin on dystrophic mice (C57BL/6J-dy). The locomotor activity of normal mice increased markedly, attaining a plateau at 8 weeks of age, whereas in dystrophic mice, it increased until the age of 7 weeks, and thereafter decreased gradually. Serum levels of creatine phosphokinase were significantly higher in dystrophic mice compared with normal mice, and dystrophic mice had a reduced muscle protein content. When 3-week-old dystrophic mice received chymostatin (1 mg/kg, i.p.), the decrease in locomotor activity was retarded, serum enzyme levels decreased significantly, and muscle protein content increased significantly. In addition, the survival time of treated dystrophic mice was prolonged. The locomotor activity, serum enzyme levels, and muscle protein content of normal mice were not affected by chymostatin. Therefore, we posit that chymostatin retarded the progression of dystrophy in mice.

Sustained proteolysis is required for human platelet activation by thrombin

A maximally effective dose of indomethacin does not prevent serotonin release and aggregation in human platelets stimulated with thrombin. Thrombin induces rapid activation of inositol phospholipids-specific phospholipase C, which is reflected by the degradation of inositides and the phosphorylation of the resultant 1,2-diacylglycerol to phosphatidic acid. Thrombin also activates protein kinase C and myosin light chain kinase as indicated by phosphorylation of the 40,000 and 20,000 dalton proteins, respectively. Leupeptin, a protease inhibitor that does not inhibit thrombin's proteolytic activity or its binding to platelet surface, is able to reverse platelet activation by thrombin when it is administered after the addition of the agonist and indomethacin. The results suggest a proteolytic-mediated pathway in transmembrane signalling involved in platelet activation by thrombin.

Vascular permeability changes by proteinase inhibitors in carrageenin-induced inflammation in rats

The effect of proteinase inhibitors such as TLCK, TPCK and leupeptin on vascular permeability was investigated in the carrageenin-air-pouch inflammation in rats. When each inhibitor was injected into the air-pouch immediately after carrageenin injection, TLCK, TPCK and leupeptin caused a rapid and significant increase in vascular permeability. The TLCK- and TPCK-induced increase declined gradually, whereas leupeptin inhibited the vascular permeability after the temporary increase. When the inhibitors were injected 5 h after carrageenin injection, TLCK and TPCK increased the vascular permeability, whereas leupeptin was without effect. Cyproheptadine, an anti-histamine and antiserotonin drug, inhibited the leupeptin-induced temporary increase, but failed to inhibit the TLCK- and TPCK-induced increase in vascular permeability. These results suggest that the leupeptin-induced increase in vascular permeability was mediated by histamine and serotonin, while TLCK and TPCK may increase vascular permeability as a result of a direct action on endothelial cells.

High-performance liquid chromatographic method for monitoring leupeptin in mouse serum and muscle by pre-column fluorescence derivatization with benzoin

A high-performance liquid chromatographic method is described for the determination of leupeptin, a possible therapeutic drug for muscular dystrophy, in mouse serum and muscle. Leupeptin is reduced with sodium borohydride to leupeptinol, and then converted to a fluorescent derivative with benzoin. The derivative is separated on a reversed-phase column (LiChrosorb RP-18) with isocratic elution and determined with fluorescence detection. The detection limits of leupeptin in serum and muscle are 250 pmol/ml (107 ng/ml) and 500 pmol/g (214 ng/g), respectively, corresponding to approximately 150 fmol each in a 100-microliters injection volume. This method is simple and sensitive enough to permit the quantification of leupeptin in biological samples from mice dosed with leupeptin.

Leupeptin selectively inhibits human platelet responses induced by thrombin and trypsin; a role for proteolytic activation of phospholipase C

Thrombin and trypsin induce serotonin release and aggregation in human platelets. Both proteases induce activation of phospholipase C as reflected by formation of inositol phosphates and phosphorylation of the resultant 1,2-diacylglycerol to phosphatidic acid. Also, thrombin and trypsin activate protein kinase C and myosin light chain kinase as indicated, respectively, by phosphorylation of the 40,000 and 20,000 dalton proteins. Leupeptin, a known inhibitor of serine proteases, blocks all the observed responses of human platelets to trypsin and thrombin. Leupeptin does not inhibit serotonin release and aggregation induced by other platelet stimuli such as collagen, platelet-activating factor, ionophore A23187, and arachidonic acid. The implication of a proteolytic-mediated pathway in the transmembrane signalling involved in platelet activation is discussed.

Metabolism of [3H]leupeptin by rat liver

Tritium-labeled leupeptin was used to study how this tripeptide proteinase inhibitor interacts with the liver, including the mechanism of its transport into the cell, its subcellular distribution after uptake, and its metabolism once in the tissue. Experiments were done in situ and in a perfused liver. At low concentrations (1 to 10 microM) the uptake of radioactive inhibitor was competed by chemically reduced leupeptin. At high concentrations at least up to 400 microM the uptake was directly proportional to the external concentration of tripeptide. Entry into the tissue essentially stopped at low temperature (less than 21 degrees C). [3H]Leupeptin initially was located in the soluble fraction of the liver homogenate and by 15 to 30 min became concentrated in the lysosome-rich fraction. During 2 h of perfusion almost 50% of [3H]leupeptin that had entered the liver was secreted intact into the bile. In addition, a portion of the leupeptin that remained in the liver was degraded during this time period.

Selective removal of heparan sulfate chains from proteoheparan sulfate with a commercial preparation of heparitinase

Procedures employing the commercial preparation of heparitinase were developed for isolating a protein-enriched core molecule from proteoheparan sulfate by selective removal of the heparan sulfate chains. Treatment of proteoheparan sulfate with the enzyme preparation caused seriously extensive degradation owing to the presence of proteolytic activity in the enzyme preparation. This effect could be avoided by using a series of protease inhibitors which prevented proteolytic degradation with less significant effect on the heparitinase activity. Application of the procedures to a purified preparation from the Engelbreth-Holm-Swarm tumor yielded a single protein-enriched core fraction with a molecular weight of approximately 450,000, as ascertained by sodium dodceyl sulfate-gel electrophoresis.

Inhibitors of lysosomal enzymes: accumulation of lipofuscin-like dense bodies in the brain

Injections of leupeptin (a thiol proteinase inhibitor) or chloroquine (a general lysosomal enzyme inhibitor) into the brains of young rats induced the formation of lysosome-associated granular aggregates (dense bodies) which closely resembled the ceroid-lipofuscin that accumulates in certain disease states and during aging. The dense material increased in a dose- and time-dependent fashion and was differentially distributed across brain regions and cell types. These observations provide clues to the origins of ceroid-lipofuscin and suggest means for studying the consequences of its accumulation.

Purification and characterization of trypsin-like enzyme from sea urchin eggs: substrate specificity and physiological role

A trypsin-like enzyme has been purified to homogeneity from eggs of the sea urchin, Strongylocentrotus intermedius. The purified enzyme efficiently hydrolyzed Z-Phe-Arg-4- methylcoumaryl -7-amide (MCA) and Pro-Phe-Arg-MCA among 12 peptidyl-Arg (or Lys)- MCAs . The substrate specificity of the enzyme was closely similar to that of the enzyme activity in the egg cortical granule exudate. Among various peptidyl-argininal (Arg-H) derivatives, Z-Phe-Arg-H and Z-Phe-Leu-Arg-H showed the strongest inhibition against both the activity of the purified enzyme and the elevation of vitelline coat. Thus, the trypsin-like enzyme of sea urchin possesses a narrow substrate specificity and participates at least in the elevation of vitelline coat during fertilization.

Role of intramuscular enzymatic changes in the development of muscular weakness in rats with experimental allergic neuritis

We investigated the role of intramuscular enzymatic changes in the development of muscular weakness in rats suffering from experimental allergic neuritis. At an initial stage without apparent clinical symptoms, enzymatic changes of similar types occurred in the muscles of the forelimbs and hind limbs. At a later stage when the weakness appeared in the hind limb but not in the forelimb, dissociation of the pattern of the enzymatic changes occurred between the two limbs. Comparison of the intramuscular enzymatic changes between the two stages and between the two limbs suggested that the increased activities of aminopeptidases and endopeptidases play some important roles in the development of muscular weakness in this experimental model. Low molecular weight protease inhibitors may thus be worthy of a trial in this disease condition.

Structural comparisons of wild-type and nuclear transport-defective simian virus 40 large tumor antigens

PARA(nT) is a defective SV40-adenovirus 7 hybrid virus which contains the entire early region of the SV40 genome and codes for the synthesis of SV40 large tumor antigen (T-ag). A transport-defective variant of this hybrid, PARA(cT), encodes T-ag that is not transported to the nucleus, but accumulates in the cytoplasm. The structures of T-ags extracted from wild-type (WT) SV40-, PARA(nT)-, and PARA(cT)-infected cells were compared by peptide mapping. All three types of T-ag underwent considerable degradation when extracted using Tris-buffered Nonidet P-40 at pH 8.0. The addition of 200 microM leupeptin to the extraction buffer significantly inhibited this degradation. Comparison of methionine-containing tryptic peptides revealed no differences among the T-ags, suggesting that their primary structures are similar or identical. Phosphopeptide mapping revealed no differences between SV40- and PARA(nT)-encoded T-ags. In contrast, PARA(cT)-encoded T-ag lacked a prominent phosphopeptide that was present in both of the others. The possible relevance of this difference in phosphorylation to the transport defect is discussed.

Enzymatic changes in dystrophic mice and their age dependency

The activities of 14 different aminopeptidases, 5 endopeptidases, 4 glycosidases, phosphatase, esterase, and ribonuclease (RNase) were measured in the muscle and bone of 12 normal controls and 12 dystrophic mice. In most cases the activity of these enzymes was significantly elevated in the muscle of the dystrophic mice. In the muscle of the controls the activity of aminopeptidase A (AP-A), Leu-AP, Trp-AP, Gly-Pro-AP, and RNase tended to decrease with the increasing age of the animal, whereas that of AP-B and Pro-AP tended to increase. This mode of age-related regression was entirely different in dystrophic muscle. The enzymatic changes in the bone of the dystrophic mice were milder but more or less analogous to those in muscle. These findings should be important in further elucidating the mode of protein degradation in dystrophic muscle and in aiding in the selection of appropriate therapeutic agents including the low-molecular-weight inhibitors.

Identification of Ca2+-activated neutral protease in the peripheral nerve and its effects on neurofilament degeneration

Rat sciatic nerve segments were incubated in five different media. Disappearance of neurofilament (NF) triplet proteins (200K, 160K, and 68K MW) occurred in medium containing Ca2+ and was inhibited by the addition of E-64-c or leupeptin. Therefore, the presence in the peripheral nerve of an enzyme whose properties are similar to those of Ca2+-activated neutral protease (CANP) is suggested. The extraction of crude CANP from rat sciatic nerve was performed. CANP activity was completely recovered (0.129 +/- 0.008 U/g) in the precipitate salted out by the addition of 0 to 50% saturated ammonium sulfate to the soluble fraction of the peripheral nerve (crude CANP). Properties of the crude CANP were examined using NF as a substrate and were found to be similar to those of the CANP extracted from skeletal muscle. Identification of the crude CANP with the CANP extracted from rat skeletal muscle was performed using the immunoreplica method. Bands corresponding to 73K were detected in both CANPs.

Two different modes of enzymatic changes in serum with progression of Duchenne muscular dystrophy

Nineteen serum enzymes from patients with Duchenne muscular dystrophy and asthma, and normal subjects were studied. These enzymes include aminopeptidases, cathepsin C, angiotensin-converting enzyme, serine proteinase, sulphatase, phosphatase, esterases and ribonuclease. The enzymatic changes in dystrophic patients were related to two parameters: severity of the disease as judged from symptomatology, and duration of the disease. Most of the enzyme levels tested were increased in milder cases, but they tended to decrease with severity of the disease. On the other hand, there was a group of enzymes showing just opposite tendencies: serine proteinase, cathepsin C and ribonuclease. Even when viewed from the relationship to duration of the disease, the above mentioned grouping of enzymes was generally valid. Most of the enzyme levels, including those routinely applied as clinical parameters, tended to decrease, logarithmically, with an increase in duration of the disease. On the contrary, some others, including serine proteinase, cathepsin C and ribonuclease, tended to increase toward their control levels. Such tendencies were not found in the patients with asthma. The discrepancy between the above two groups of enzymes may have some implications for the process of protein degradation in dystrophic patients.

Tissue and subcellular distribution of enzymes inactivating leupeptin

Leupeptin, a proteinase inhibitor obtained from culture filtrates of Streptomyces sp., has been proposed as a valuable agent for the restriction of proteolysis in vivo. We have previously shown that mammalian tissues possess an enzymic system that is capable of inactivating leupeptin (Beynon RJ, Brown CP & Butler PE, 1981, Acta Biol. Med. Germ. 40, 1539-1546). This paper demonstrates the ubiquitous distribution of the inactivating system throughout mammalian tissues and provides evidence for the location of the enzyme(s) in the soluble fraction of the cell.