A selective assay for endooligopeptidase A based on the cleavage of fluorogenic substrate structurally related to enkephalin

Thimet Oligopeptidase Biochemical and Biological Significances: Past, Present, and Future Directions

Thimet oligopeptidase (EC 3.4.24.15; EP24.15, THOP1) is a metallopeptidase ubiquitously distributed in mammalian tissues. Beyond its previously well characterized role in major histocompatibility class I (MHC-I) antigen presentation, the recent characterization of the THOP1 C57BL6/N null mice (THOP1^−/−) phenotype suggests new key functions for THOP1 in hyperlipidic diet-induced obesity, insulin resistance and non-alcoholic liver steatosis. Distinctive levels of specific intracellular peptides (InPeps), genes and microRNAs were observed when comparing wild type C57BL6/N to THOP1^−/− fed either standard or hyperlipidic diets. A possible novel mechanism of action was suggested for InPeps processed by THOP1, which could be modulating protein-protein interactions and microRNA processing, thus affecting the phenotype. Together, research into the biochemical and biomedical significance of THOP1 suggests that degradation by the proteasome is a step in the processing of various proteins, not merely for ending their existence. This allows many functional peptides to be generated by proteasomal degradation in order to, for example, control mRNA translation and the formation of protein complexes.

Plasma Ndel1 enzyme activity is reduced in patients with schizophrenia--a potential biomarker?

Ndel1 oligopeptidase interacts with schizophrenia (SCZ) risk gene product DISC1 and mediates several functions related to neurite outgrowth and neuronal migration. Ndel1 also hydrolyzes neuropeptides previously implicated in SCZ, namely neurotensin and bradykinin. Herein, we compared the plasma Ndel1 enzyme activity of 92 SCZ patients and 96 healthy controls (HCs). Ndel1 enzyme activity was determined by fluorimetric measurements of the FRET peptide substrate Abz-GFSPFRQ-EDDnp hydrolysis rate. A 31% lower mean value for Ndel1 activity was observed in SCZ patients compared to HCs (Student's t = 4.36; p < 0.001; Cohen's d = 0.64). The area under the curve (AUC) for the Receiver Operating Characteristic (ROC) curve for Ndel1 enzyme activity and SCZ/HCs status as outcome was 0.70. Treatment-resistant (TR) SCZ patients were shown to present a significantly lower Ndel1 activity compared to non-TR (NTR) patients by t-test analysis (t = 2.25; p = 0.027). A lower enzymatic activity was significantly associated with both NTR (p = 0.002; B = 1.19; OR = 3.29; CI 95% 1.57-6.88) and TR patients (p < 0.001; B = 2.27; OR = 9.64; CI 95% 4.12-22.54). No correlation between Ndel1 enzyme activity and antipsychotic dose, nicotine dependence, and body mass index was observed. This study is the first to show differences in Ndel1 activity in SCZ patients compared to HCs, besides with a significant lower activity for TR patients compared to NTR patients. Our findings support the Ndel1 enzyme activity implications to clinical practice in terms of diagnosis and drug treatment of SCZ.

OBJECTIVE OF THE STUDY

To compare the Ndel1 enzyme activity levels of schizophrenia (SCZ) patients and healthy controls (HCs) and to correlate these values with the clinical profile and response to treatment by measuring the Ndel1 enzyme activity in human plasma.

Cloning and characterization of the human and rabbit NUDEL-oligopeptidase promoters and their negative regulation

NUDEL-oligopeptidase is a cytosolic cysteine peptidase, active towards oligopeptides and involved in the conversion and inactivation of a number of bioactive peptides. This protein interacts with neuronal proteins and is essential for brain development and cortical organization during embryogenesis. In this study, 5'-flanking sequences of the human and rabbit NUDEL-oligopeptidase gene were cloned into the pGL3 reporter gene vector and the promoter activity of the full-length fragment and deletions series was measured in transient transfection assays using two different cell lines, namely, C6 rat glioma and NH15 human neuroblastoma. Overall, a very similar pattern of promoter activity was obtained for both rabbit and human NUDEL-oligopeptidase promoter sequences, and their respective serial deletion constructs upon transient transfection into these cell lines. The only exception was for the longest rabbit upstream sequence that displayed about 1.8-fold higher luciferase expression upon transfection into NH15 neuronal cells than that observed upon transfection into C6 glioma cells. On the other hand, no significant difference was observed for the human longest sequence. These results are in good agreement with the expression pattern of NUDEL-oligopeptidase in human and rabbit tissues.

Melanoma heterogeneity: differential, invasive, metastatic properties and profiles of cathepsin B, D and L activities in subclones of the B16F10-NEX2 cell line

Tumour cell lines and in vivo growing tumours are heterogeneous, comprising different cell clones. To understand why some cells primarily invade a tissue, while others are more apt to metastasize, several clones from the established B16F10-Nex2 cell line were isolated and 10 viable cells of each clone were injected intravenously into C57Bl/6 and Balb/c mice. Two cell clones (Nex2B and Nex2D) showed contrasting metastatic abilities. Clone 2D rather than clone 2B colonized the lungs of both mice after intravenous injection. Surprisingly, clone 2B grew more rapidly than 2D after subcutaneous implantation, significantly reducing the survival of injected mice. Clearly, dissociation between subcutaneous growth and metastatic ability was observed in clones from the same tumour cell lineage. Clone Nex2B continuously released proteolytic activity, including cathepsin B, and showed a greater capacity to invade Matrigel than clone Nex2D. Clone Nex2D accumulated cathepsins B, D and L intracellularly and released a moderate proteolytic activity in vitro that was inhibited with the time of incubation. E-64-treated Nex2B cells injected subcutaneously showed a significant delay in tumour development and increased survival of challenged animals. A similar result was obtained on treatment of clone 2B with chagasin, a cysteine proteinase inhibitor from Trypanosoma cruzi, even at 2 microM. Clone Nex2D was less sensitive to pretreatment with inhibitors of cysteine proteases for tumour development in vivo. Our results suggest that, in a tumour cell population, cells dissociate into metastatic and non-metastatic subtypes, and that release or accumulation of cathepsins can be a differential trait of these cells.

The one-bead two-compound assay for solid phase screening of combinatorial libraries

Fluorescent quenched substrate libraries are a very powerful tool for investigation of protease activity and specificity. Particularly, libraries where the fluorescent resonance energy transfer (FRET) pair is 3-nitrotyrosine and 2-amino-benzamide are easy to prepare by split and combine synthesis to yield a one-bead one-compound library format. The solid support is critical for the successful hydrolysis of the resin-bound substrates. For this purpose, a range of highly porous poly(ethylene glycol) (PEG)-based resins have been developed. Active substrates yield highly fluorescent beads and these are selected under a fluorescence microscope or isolated on a bead sorter. Edman sequence analysis yields the substrate sequence, the cleavage point, and the degree of conversion. The method gives a complete map of the substrate specificity, and substrates with high affinity for the active site can be selected. These may in turn be used as inhibition indicators in a second solid phase library assay for enzyme inhibition where each single bead is transformed into an assay container. The substrate is attached to temporarily shielded functional groups after completion of inhibitor library synthesis. By using a photolabile linker and ladder synthesis, the active inhibitors may be rapidly identified by mass spectrometry. In each bead, the putative inhibitor competes with the substrate attached for binding to the enzyme, and when the inhibitor binds strongly, the substrate remains intact and quenched. Thus dark beads indicate inhibitors, and these may be isolated using a bead-sorter and the structure determined by mass spectrometry. A selection of the best substrates and inhibitors should always be resynthesized for solution kinetics and confirmation of the results obtained on solid support. The inhibitor assay is almost free from false positives, which is a consequence of combining the binding of the protease to the inhibitor with observation of activity toward a FRET substrate. The K(i) of the identified inhibitors are typically in the nM range.

A prothrombin activator serine protease from the Lonomia obliqua caterpillar venom (Lopap) biochemical characterization

Lonomia obliqua venom causes a severe consumptive coagulopathy, which can lead to a hemorrhagic syndrome. The crude bristles extract displays a procoagulant activity due to a Factor X and to a prothrombin activating activity. Here, we describe a 69 kDa prothrombin activator serine protease purified from L. obliqua caterpillar bristle extract using gel filtration (Sephadex G 75) and HPLC (C(4) column). The purified protein was able to activate prothrombin in a dose-dependent manner, and calcium ions increased this activity. The prothrombin-derived fluorogenic peptide (Abz-YQTFFNPRTGSQ-EDDnp) had its main cleavage site at the Arg-Thr bond. The kinetic parameters obtained for this substrate were Kmapp of 4.5 microM, kcat of 5.32 s(-1), and a kcat/Kmapp of 1.2 x 10(6) M(-1) s(-1). The prothrombin fragments generated by the purified enzyme corresponded to the molecular masses of prethrombin 2, fragment 1, fragment 2, and thrombin as seen in SDS-PAGE. The thrombin generated was able to clot purified fibrinogen. The partial amino acid sequence of the purified protein, named Lopap (L. obliqua prothrombin activator protease), showed no similarity to any known prothrombin activator.

Molecular and immunochemical evidences demonstrate that endooligopeptidase A is the predominant cytosolic oligopeptidase of rabbit brain

Oligopeptidases are tissue endopeptidases that do not attack proteins and are likely to be involved in the maturation and degradation of peptide hormones and neuropeptides. The rabbit brain endooligopeptidase A and the rat testes soluble metallopeptidase (EC 3.4.24.15) are thiol-activated oligopeptidases which are able to generate enkephalin from a number of opioid peptides and to inactivate bradykinin and neurotensin by hydrolyzing the same peptide bonds. A monospecific antibody raised against the purified rabbit brain endooligopeptidase A allowed the identification of a 2. 3 kb cDNA coding for a truncated enzyme of 512 amino acids, displaying the same enzymatic features as endooligopeptidase A. In spite of all efforts, employing several strategies, the full-length cDNA could not be cloned until now. The analysis of the deduced amino acid sequence showed no similarity to the rat testes metalloendopeptidase sequence, except for the presence of the typical metalloprotease consensus sequence [HEXXH]. The antibody raised against recombinant endooligopeptidase A specifically inhibited its own activity and reduced the thiol-activated oligopeptidase activity of rabbit brain cytosol to less than 30%. Analysis of the endooligopeptidase A tissue distribution indicated that this enzyme is mainly expressed in the CNS, whereas the soluble metallo EC 3.4.24.15 is mainly expressed in peripheral tissues.

Secretion of metalloendopeptidase 24.15 (EC 3.4.24.15)

The metalloendopeptidase EP24.15 (EC3.4.24.15) is a neuropeptide-metabolizing enzyme present in neural and endocrine tissues, presumably functioning extracellularly. Because the majority of the EP24.15 activity is identified in the soluble fraction of cellular homogenates, suggesting that the enzyme is primarily an intracellular protein, we addressed the issue of how EP24.15 arrives in the extracellular environment. We utilized a model system of neuroendocrine secretion, the AtT20 cell. According to both enzymatic activity and immunologic assays, EP24.15 was synthesized in and released from AtT20 cells. Under basal conditions and after stimulation by corticotropin-releasing hormone or the calcium ionophore A23187, EP24.15 activity accumulated in the culture medium. This secretion was not attributable to cell damage, as judged by the absence of release of cytosolic enzyme markers and the ability to exclude trypan blue dye. Pulse-chase analysis and subcellular fractionation of AtT20 cell extracts suggested that the mechanism of EP24.15 secretion is not solely via classical secretory pathways. Additionally, drugs which disrupt the classical secretory pathway, such as Brefeldin A and nocodazole, blocked A23187-stimulated EP24.15 release yet had no effect on basal EP24.15 release, suggesting differences in the basal and stimulated pathways of secretion for EP24.15. In summary, EP24.15 appears to be secreted from AtT20 pituitary cells into the extracellular milieu, where the enzyme can participate in the physiologic metabolism of neuropeptides.

Purification and characterization of a neutral endopeptidase-like enzyme from human urine

OBJECTIVE

The aims of this study were to purify and characterize a neutral endopeptidase-like enzyme (NEP-like) in human urine and propose a rapid, sensitive and specific assay for this enzyme using the fluorogenic substrate Abz-FDQ-EDDnp, where Abz = O-aminobenzoic acid and EDDnp = N-(2,4-dinitrophenyl)ethylenediamine.

METHODS

Soluble urinary NEP was purified from human urine using a DEAE-cellulose Cellex D column and gel filtration on an AcA-44 column. NEP-like activity was assayed by its ability to hydrolyse bradykinin (BK) and the fluorogenic substrates Abz-BKQ-EDDnp and Abz-FDQ-EDDnp. The Km was determined using Abz-FDQ-EDDnp as a substrate. The hydrolysis products of BK and Abz-FDQ-EDDnp were analysed by high-performance liquid chromatography (HPLC). The mol. wt was estimated by polyacrylamide gel electrophoresis and the enzyme analysed by Western blot using the antibody obtained from purified recombinant NEP expressed in Pichia pastoris yeast.

RESULTS

The NEP-like was purified from human urine until homogeneity and presented a mol. wt of 94000. The substrate Abz-FDQ-EDDnp was selectively hydrolysed at the F-D bond by NEP-like and by recombinant NEP. For this substrate, the NEP-like activity was maximal at pH 7.0, although a small peak of activity was observed at pH 8.0, and the determined Km was 14 microM. The enzymatic activity was inhibited by thiorphan and phosphoramidon. In Western blot analysis, NEP-like reacted strongly with a polyclonal antibody for NEP.

CONCLUSION

A NEP-like enzyme was purified from human urine. Based on the mol. wt of the isolated NEP-like enzyme, it was concluded that this enzyme was produced in the kidney. In the kidney, this enzyme may cleave the kinins filtered through the glomerulus and also the kinins produced in the distal nephron. An internally quenched fluorogenic peptide, Abz-FDQ-EDDnp, was selectively hydrolysed by NEP-like and by recombinant NEP.

Structural features that make oligopeptides susceptible substrates for hydrolysis by recombinant thimet oligopeptidase

A systematic analysis of the peptide sequences and lengths of several homologues of bioactive peptides and of a number of quenched-fluorescence (qf) opioid- and bradykinin-related peptides was performed to determine the main features leading the oligopeptides to hydrolysis by the recombinant rat testis thimet oligopeptidase (EC 3.4.24.15). The results indicate that a minimum substrate length of six amino acids is required and that among the oligopeptides six to thirteen amino acid residues long, their susceptibility as substrates is highly variable. Thimet oligopeptidase was able to hydrolyse, with similar catalytic efficiency, peptide bonds having hydrophobic or hydrophilic amino acids as well as proline in the P1 position of peptides, ranging from a minimum of six to a maximum of approximately thirteen amino acid residues. An intriguing observation was the shift of the cleavage site, at a Leu-Arg bond in qf dynorphin-(2-8) [qf-Dyn2-8; Abz-GGFLRRV-EDDnp, where Abz stands for o-aminobenzoyl and EDDnp for N-(2,4-dinitrophenyl)ethylenediamine], to Arg-Arg in qf-Dyn2-8Q, in which Gln was substituted for Val at its C-terminus. Similarly, a cleavage site displacement was also observed with the hydrolysis of the internally quenched-fluorescence bradykinin analogues containing Gln at the C-terminal position, namely Abz-RPPGFSPFR-EDDnp and Abz-GFSPFR-EDDnp are cleaved at the Phe-Ser bond, but Abz-RPPGFSPFRQ-EDDnp and Abz-GFSPFRQ-EDDnp are cleaved at the Pro-Phe bond.

Fluorogenic substrates for proteases based on intramolecular fluorescence energy transfer (IFETS)

A prospective class of intramolecular fluorescence energy transfer substrates (IFETS) is described. In contrast to the known chromogenic and fluorogenic substrates that are used widely in the scientific and medical research, IFETS allow to control the enzymatic cleavage at any point of the peptide chain and thus permit simultaneous studies of enzymes of different specificity. We discuss the main types of donor and acceptor, their advantages and drawbacks and the effectiveness of exited-state energy transfer between them. High sensitivity and selectivity of IFETS in the assay of proteinases was demonstrated. They prove to be a very useful and very promising instrument for enzymology and medicine.

Liver bradykinin-inactivating-endopeptidase is similar to the metalloendopeptidase (EC 3.4.24.15)

The bradykinin-inactivating-endopeptidase (BIE) removal from rat liver, by perfusing the organ with 0.05% Triton X-100, achieved its maximum at 10 min of perfusion and falls to 50% of the maximum in 30 min, a pattern similar to AST removal. Using an internally quenched fluorescent BK analogue (Abz-RPPGFSPFRQ-EDDnp) we further characterized this enzyme: it is activated by low concentrations of 2-mercaptoethanol, inhibited by p-hydroxymercuribenzoate, o-phenanthroline and EDTA, and is resistant to enalapril, E-64 and PMSF. These results suggest that BIE is a metalloendopeptidase containing a thiol group important for its activity. BIE also hydrolyses the peptides Abz-GGFLRRVQ-EDDnp, Abz-GPQGLAGQ-EDDnp, Abz-FRSVQ-EDDnp, and Abz-ARVRRANSFLQ-EDDnp. All these properties are very similar to those described or assayed by us for EC 3.4.24.15, isolated initially from rat testes and then from several organs of different animals. Both BIE and EC 3.4.24.15: hydrolyze the F5S6 bond of the BK fluorescent substrate; are efficiently inhibited by Orlowski specific inhibitor (CFP-AAF-pAB, Ki 4.4 x 10(-7) M and 1.25 x 10(-7) M, respectively); have the same electrophoretic mobility in SDS-PAGE (Mr 78,000); and are both recognized by three polyclonal antibodies raised against rat testes EC 3.4.24.15. In conclusion, BIE appears to be EC 3.4.24.15.

Purification and characterization of a dynorphin-processing endopeptidase

Dynorphin B (Dyn B-13, also known as rimorphin) is generated from Dyn B-29 (leumorphin) by the cleavage at a single Arg residue. An enzymatic activity capable of processing at this monobasic site has been previously reported in neurosecretory vesicles of the bovine pituitary and pituitary-derived cell lines. This enzyme termed "the dynorphin-converting enzyme" (DCE) has been purified to apparent homogeneity from the neurointermediate lobe of the bovine pituitary using hydrophobic chromatography on phenyl-Sepharose, preparative isoelectrofocusing in a granulated gel between pH 4 to 6.5, and non-denaturing electrophoresis on 5% polyacrylamide gel. DCE exhibits a pI of about 5.1 and a molecular mass of about 54 kDa under reducing conditions. DCE is a metallopeptidase and exhibits a neutral pH optimum. Specific Inhibitors of soluble metallopeptidases such as enkephalinase (EC 3.4.24.11) or enkephalin generating neutral endopeptidase (EC 3.4.24.15) do not inhibit DCE activity indicating that DCE is distinct from these two enzymes. Cleavage site determination with matrix-assisted laser desorption ionization time of flight (MALDITOF) mass spectrometry shows that DCE cleaves the Dyn B-29 N terminus to the Arg14 generating Dyn B-13 and Dyn B-(14-29). Among other peptides derived from Dyn B-29, DCE cleaves only those peptides that fit the predicted "consensus motif" for monobasic processing. These data are consistent with a broader role for the dynorphin converting enzyme in the biosynthesis of many peptide hormones and neuropeptides by processing at monobasic sites.

Rat thimet oligopeptidase: large-scale expression in Escherichia coli and characterization of the recombinant enzyme

The coding sequence for rat testis thimet oligopeptidase (TOP) (EC 3.4.24.15) was placed under the control of the T7 polymerase/promoter system. Cultures of Escherichia coli transfected with the resulting plasmid expressed the enzyme as a soluble cytoplasmic protein. Medium-scale cultures allowed isolation of the enzyme in quantities of tens of milligrams. The availability of the recombinant enzyme permitted the determination of such chemical properties as epsilon 280 (48,960), zinc content (2 atom/molecule) and available thiol content (8-10/molecule) for TOP. The recombinant enzyme showed the catalytic activities previously reported for the naturally occurring enzyme, so that we can now conclude with confidence that these are all due to TOP and there is no need to postulate the existence of separate 'Pz-peptidase' or 'endo-oligopeptidase A' enzymes.

Thimet oligopeptidase specificity: evidence of preferential cleavage near the C-terminus and product inhibition from kinetic analysis of peptide hydrolysis

The substrate-size specificity of human thimet oligopeptidase (EC 3.4.24.15) was investigated with oligomers of glycyl-prolyl-leucine (GPL)n where n = 2, 3, 4 and 5. These peptides were cleaved only at Leu-Gly bonds to give GPL as the single final product. Hydrolysis was most rapid with (GPL)3 and slowest with (GPL)5. The more water-soluble oligomers of Gly-Hyp-Leu showed the same trend. (Gly-Hyp-Leu)6 was not hydrolysed, consistent with the previous finding that substrates larger than 17 amino acids are not cleaved by thimet oligopeptidase. The cleavage of (GPL)3 to GPL fitted a sequential first-order model. First-order kinetics were unexpected as the initial substrate concentration was greater than Km. The anomaly was also seen during the cleavage of bradykinin and neurotensin, and in these cases first-order behaviour was due to potent competitive inhibition by the C-terminal product. The sequential mechanism for (GPL)3 breakdown by thimet oligopeptidase does not discriminate between initial cleavages towards the N- or C-terminus. As isoleucine is an unfavourable residue in P1, substrates were made in which selected leucine residues were replaced by isoleucine. GPL--GPI--GPL (where--represents the bond between the tripeptide units) was resistant to hydrolysis and GPI--GPL--GPL was cleaved only at the -Leu-Gly- bond. Experiments with isoleucine-containing analogues of (Gly-Hyp-Leu)4 showed that thimet oligopeptidase preferred to cleave these peptides near the C-terminus.

Characterization of an endooligopeptidase A-like protein in PC12 cells: activity modulation by cAMP but not by basic fibroblast growth factor

Endooligopeptidase A is a putative neuropeptide-metabolizing enzyme. It converts small enkephalin-containing peptides into the corresponding enkephalins and inactivates biopeptides such as bradykinin and neurotensin in vitro. We investigated the presence of endooligopeptidase A in PC12 cells. This cell line was derived from a rat pheochromocytoma tumor and resembles fetal chromaffin cell. Depending on the supplements added to the cell culture, this cell line can be differentiated into mature chromaffin cell or sympathetic neuron-like cell. Endooligopeptidase A activity was measured in soluble cellular extracts using a specific fluorogenic substrate QF-ERP7. The PC12 endooligopeptidase A-like activity shared similar but not identical biochemical properties with rabbit brain endooligopeptidase A. Similarly to rabbit brain endooligopeptidase A, the PC12 endooligopeptidase A-like activity was enhanced by DTT, totally inhibited by DTNB and 1-10 Phenanthroline, partially inhibited by cFP-AAF-pAb, and not affected by PMSF. Furthermore, the PC12 endooligopeptidase A-like activity displayed identical elution profile as rabbit brain endooligopeptidase A in gel filtration and anion-exchange chromatography. In addition, an antiserum raised against rabbit brain endooligopeptidase A cross-reacted with a 71 kDa component from PC12 cell extracts in Western blotting and was also able to partially neutralize the PC12 endooligopeptidase A-like activity. Treatment of PC12 cells with basic fibroblast growth factor (bFGF), a neurotrophic factor for this cell line, did not modify the specific activity of this enzyme. However, cAMP analogs decreased the specific activity of the enzyme. These results indicate the presence of an endooligopeptidase A-like activity in PC12 cells which is modulated by cAMP but not by bFGF.

Isolation and characterization of a new bradykinin potentiating octapeptide from gamma-casein

Peptides that display bradykinin-potentiating activity have been obtained from a number of distinct sources, such as snake venoms, fibrinogen, and casein. This paper describes the isolation and sequencing of a novel bradykinin-potentiating peptide, generated by tryptic hydrolysis of the gamma-casein chain. No homology was found to other known vasoactive or vasopotentiating peptides. The octapeptide Tyr-Pro-Val-Gln-Pro-Phe-Thr-Glu, corresponding to the gamma-casein(114-121) sequence, was isolated from the tryptic hydrolysis of gamma-casein and also synthesized by solid-phase peptide synthesis. Both natural and synthetic peptides had the same retention time in HPLC and displayed a selective potentiating activity on isolated guinea-pig ileum for bradykinin and Lys-bradykinin but were not able to potentiate the effects of Met-Lys-bradykinin, Ile-Ser-bradykinin, angiotensin II, acetylcholine, or histamine. Intravenous injections of bradykinin and of bradykinin-potentiating octapeptide produced a persistent hypotension in conscious rats, a pattern that was not obtained when the octapeptide was replaced by captopril. This bradykinin-potentiating octapeptide is a strong competitive inhibitor of endo-oligopeptidase A (EC 3.4.24.15, formerly EC 3.4.22.19), but it has low inhibitory potency towards angiotensin-converting enzyme (EC 3.4.15.1). Thus, our results suggest that other peptidases in addition to angiotensin-converting enzyme, such as endo-oligopeptidase A, may contribute to the reduction of the effective concentration of bradykinin in the circulation.

Portion-mixing peptide libraries of quenched fluorogenic substrates for complete subsite mapping of endoprotease specificity

A solid-phase assay for the complete subsite mapping of the active site of endoproteases has been developed. A library of resin-bound protease substrates was synthesized both on kieselguhr-supported polyamide resin and on a polyethylene glycol-poly-(N,N-dimethylacrylamide) copolymer type of resin that allows proteases to diffuse into the interior and perform their catalytic activity. Anthranilic acid and 3-nitrotyrosine were used as an efficient donor-acceptor pair for the resonance energy transfer. The synthesis was performed in a manual library generator that allows simple wet mixing of the beads and parallel washing procedures. After treatment with subtilisin Carlsberg, fluorescing beads were collected and subjected to peptide sequencing, affording the preferred sequences, their cleavage bond, and a semiquantitative estimation of the turnover. A statistical distribution of preferred amino acids was obtained for each subsite. The result was compared with data from kinetic studies in solution.

Structural requirements of bioactive peptides for interaction with endopeptidase 22.19

A series of biologically active peptides and related compounds (opioid peptides, neurotensin, and bradykinin) were used as substrates or competitive inhibitors to study the structural requirements for peptide interaction with endopeptidase 22.19. The kinetics of hydrolysis of these peptides indicated that, in contrast to other proteases, the substrate specificity of endopeptidase 22.19 is not determined by the amino acids flanking the sensitive bonds of the substrates. The competition between bioactive peptide analogues and the quenched fluorescence substrate of endopeptidase 22.19 indicated that their length and their flexibility may be the dominant factors to explain their binding specificities. These peculiar features of endopeptidase 22.19 may be of importance to understand the physiological processes of conversion and inactivation of biologically active peptides.

Effects of morphine withdrawal syndrome on endo-oligopeptidase (EC 3.4.22.19) activity

Endo-oligopeptidase (EC 3.4.22.19), an enzyme capable of generating enkephalin by single cleavage from enkephalin-containing peptides, was examined in several areas of the central nervous system (CNS) as well as in the immune and endocrine tissues of rats chronically treated with morphine and submitted to naloxone-induced withdrawal. A specific fluorogenic substrate was used to determine the endopeptidase 22.19 activity. A non-uniform increase in endopeptidase 22.19 activity was detected in the CNS. The highest increase in endopeptidase 22.19 specific activity was found in the dorsal hippocampus (about 3.5-fold higher than control), followed by occipital and frontal cortex, substantia nigra, thalamus and hypothalamus. In peripheral tissues, a significant decrease of endopeptidase 22.19 was observed in the pineal gland, whereas the morphine withdrawal syndrome caused a slight but significant increase in lymphoid tissues such as lymph nodes and thymus. These findings are indicative of a possible participation of endopeptidase 22.19 in naloxone-induced withdrawal.

Human thimet oligopeptidase

We have purified human thimet oligopeptidase to homogeneity from erythrocytes, and compared it with the enzyme from rat testis and chicken liver. An antiserum raised against rat thimet oligopeptidase also recognized the human and chicken enzymes, suggesting that the structure of the enzyme has been strongly conserved in evolution. Consistent with this, the properties of the human enzyme were very similar to those for the other species. Thus human thimet oligopeptidase also is a thiol-dependent metallo-oligopeptidase with M(r) about 75,000. Specificity for cleavage of a number of peptides was indistinguishable from that of the rat enzyme, but Ki values for the four potent reversible inhibitors tested were lower. In discussing the results, we consider the determinants of the complex substrate specificity of thimet oligopeptidase. We question whether substrates containing more than 17 amino acid residues are cleaved, as has been suggested. We also point out that the favourable location of a proline residue and a free C-terminus in the substrate may be as important as the hydrophobic residues in the P2, P1 and P3' positions that have been emphasized in the past.

Intramolecularly quenched fluorogenic peptide substrates for human renin

Six intramolecularly quenched fluorogenic peptides related to the sequences Phe8 to His13, His6 to His13, and Tyr4 to His13 of the human angiotensinogen, containing o-aminobenzoyl (Abz) and ethylenediamine dinitrophenyl (EDDnp) groups at amino- and carboxyl-terminal amino acids residues, were synthesized by classical solution methods. The Leu-Val is the only bond of all obtained peptides that was hydrolyzed by human renin with different degrees of purity and was resistant to hydrolysis by pig renin and cathepsin D. The hydrolysis of Abz-His-Pro-Phe-His-Leu-Val-Ile-His-EDDnp by human renin was inhibited by a highly specific transition-state analog of angiotensinogen (IC50 = 7.8 x 10(-9) M), described by K. Iizuka et al. (1990, J. Med. Chem. 33, 2707-2714). Therefore, specific and sensitive substrates for the continuous assay of human renin in which as little as 70 microGU of human renin could be detected by Abz-Phe-His-Leu-Val-Ile-His-EDDnp were described. The optimal pHs of hydrolysis of the substrates were in the range 4 to 6.

Presence of endo-oligopeptidase (EC 3.4.22.19), a putative neuropeptide-metabolizing endopeptidase in cells of the immune system

Neuropeptides have been shown to modulate the bidirectional communication between the central nervous and immune systems. The endooligopeptidase (EC 3.4.22.19), originally isolated and characterized in the nervous tissue, was shown to hydrolyse several neuropeptides and to generate enkephalin from enkephalin-containing peptides. This report shows the presence of endopeptidase 22.19 in the rat immune system using both biochemical and immunochemical methods. The specific activity of endopeptidase 22.19 in soluble fraction of lymphocytes was 3-4-fold higher than the one found in the nervous tissue. Among rat blood cells the highest specific activity of endopeptidase 22.19 was found in T lymphocytes, being 2.5-fold higher than the activity found in other leukocytes. Immunocytochemical studies performed in tissues and cells of the immune system indicate the presence of endopeptidase 22.19-like enzyme in all types of leukocytes. The occurrence of this enzyme in cells of the immune system can be considered an important step in understanding the metabolism of neuropeptides in the immune system as well as its possible participation as a regulatory enzyme in neuroimmunomodulation.

New intramolecularly quenched fluorogenic peptide substrates for the study of the kinetic specificity of papain

A series of new substrates for determining the catalytic activity of cysteine proteinases is described. The rate of hydrolysis by papain was monitored by a fluorescence continuous assay based on internal resonance energy transfer using 5-[(2-aminoethyl)amino]naphtalene-1-sulfonic acid (EDANS) and 4-(4-dimethylaminophenylazo)benzoic acid (DABCYL) as fluorescent donor and quenching acceptor, respectively, in peptides with the general structure: DABCYL-Lys-Phe-Gly-Xxx-Ala-Ala-EDANS. The substrates were used to evaluate the effect of amino acid structure in the S1' position on the kinetic parameters for papain catalyzed hydrolysis.

Endo-oligopeptidase A, a putative enkephalin-generating enzyme, in the vertebrate retina

Endo-oligopeptidase A, EC 3.4.22.19, converts small enkephalin-containing peptides into the corresponding enkephalins in vitro. We investigated the presence of endooligopeptidase A in the retina and its possible colocalization with enkephalins in retinal neurons. The specific activity of endo-oligopeptidase. A found in pigeon retinae (30.3 +/- 7.3 mU/mg, mean +/- standard deviation) was four times higher than in rabbit retinae (7.0 +/- 1.1 mU/mg). The enzyme activity was not modified by EDTA, but it was enhanced by dithiothreitol and inhibited by zinc and 5,5'-dithiobis(2-nitrobenzoic acid). Immunohistochemical experiments with a purified antiserum against rabbit endo-oligopeptidase A revealed labeled neurons in both the inner nuclear layer and the ganglion cell layer of pigeon and rabbit retinae. Double-labeling immunofluorescence experiments demonstrated that about 90% of neurons containing endo-oligopeptidase A-like immunoreactivity also contained [Leu5]-enkephalin-like immunoreactivity. These colocalization results may represent an important step toward the demonstration of the possible involvement of endo-oligopeptidase A in enkephalin generation in vivo.

A survey of vasoactive peptide metabolizing enzymes in the rat mesenteric arterial bed perfusate

We have demonstrated that the isolated perfused rat mesenteric arterial bed (MAB) secretes peptidases capable of metabolizing bradykinin and angiotensin I. The major degradative pathway of bradykinin by enzymes found in the rat MAB perfusate was mediated by carboxypeptidase A-like activity, whereas angiotensin 1 degradation followed two main routes, one attributable to a carboxypeptidase A-like enzyme and the other to an endopeptidase. This latter enzyme seems to be a novel serine peptidase capable of releasing angiotensin II directly from both angiotensin I and renin substrate tetradecapeptide. The rat MAB perfusate was also shown to contain additional endo- and exopeptidases that might play a role in the metabolism of other vasoactive peptides. Our finding that isolated rat MAB secretes peptidases into the perfusion medium indicates that peptide processing within the microvasculature environment may be effected by enzymes besides those normally found in plasma or associated with cell membranes.