Cleavage of substance P to an N-terminal tetrapeptide and a C-terminal heptapeptide by a post-proline Cleaving enzyme from bovine brain

The Role of Substance P Within Traumatic Brain Injury and Implications for Therapy

This review examines the role of the neuropeptide substance P within the neuroinflammation that follows traumatic brain injury. It examines it in reference to its preferential receptor, the neurokinin-1 receptor, and explores the evidence for antagonism of this receptor in traumatic brain injury with therapeutic intent. Expression of substance P increases following traumatic brain injury. Subsequent binding to the neurokinin-1 receptor results in neurogenic inflammation, a cause of deleterious secondary effects that include an increased intracranial pressure and poor clinical outcome. In several animal models of TBI, neurokinin-1 receptor antagonism has been shown to reduce brain edema and the resultant rise in intracranial pressure. A brief overview of the history of substance P is presented, alongside an exploration into the chemistry of the neuropeptide with a relevance to its functions within the central nervous system. This review summarizes the scientific and clinical rationale for substance P antagonism as a promising therapy for human TBI.

Angiotensin-Related Peptides and Their Role in Pain Regulation

Angiotensin (Ang)-generating system has been confirmed to play an important role in the regulation of fluid balance and blood pressure and is essential for the maintenance of biological functions. Ang-related peptides and their receptors are found throughout the body and exhibit diverse physiological effects. Accordingly, elucidating novel physiological roles of Ang-generating system has attracted considerable research attention worldwide. Ang-generating system consists of the classical Ang-converting enzyme (ACE)/Ang II/AT1 or AT2 receptor axis and the ACE2/Ang (1-7)/MAS1 receptor axis, which negatively regulates AT1 receptor-mediated responses. These Ang system components are expressed in various tissues and organs, forming a local Ang-generating system. Recent findings indicate that changes in the expression of Ang system components under pathological conditions are involved in the development of neuropathy, inflammation, and their associated pain. Here, we summarized the effects of changes in the Ang system on pain transmission in various organs and tissues involved in pain development process.

Continuous infusion of substance P into rat striatum relieves mechanical hypersensitivity caused by a partial sciatic nerve ligation via activation of striatal muscarinic receptors

Previous studies have demonstrated that continuous substance P (SP) infusion into the rat striatum attenuated hind paw formalin-induced nociceptive behaviors and mechanical hypersensitivity via a neurokinin-1 (NK1) receptor dependent mechanism. However, whether there is a role of striatal infusion of SP on chronic, neuropathic pain has yet to be demonstrated. The present study investigated the effect of continuous SP infusion into the rat striatum using a reverse microdialysis method is antinociceptive in a rat model of chronic, mononeuropathic pain. Two weeks after partial sciatic nerve injury, the ipsilateral hind paw demonstrated mechanical hypersensitivity. Infusion of SP (0.2, 0.4, or 0.8 μg/mL, 1 μL/min) for 120 min into the contralateral striatum dose-dependently relieved mechanical hypersensitivity. The antinociceptive effect of SP infusion was inhibited by co-infusion with the NK1 receptor antagonist CP96345 (10 μM). Neither ipsilateral continuous infusion nor acute microinjection of SP (10 ng) into the contralateral striatum was antinociceptive. A role of striatal muscarinic cholinergic neurons is suggested since co-infusion of SP with atropine (10 μM), but not the nicotinic receptor mecamylamine (10 μM), blocked antinociception. The current study suggests that activation of striatal muscarinic receptors through NK1 receptors could be a novel approach to managing chronic pain.

Substance P in Solution: Trans-to-Cis Configurational Changes of Penultimate Prolines Initiate Non-enzymatic Peptide Bond Cleavages

We report ion mobility spectrometry and mass spectrometry studies of the non-enzymatic step-by-step degradation of substance P (subP), an 11-residue neuropeptide, with the sequence Arg1-Pro2-Lys3-Pro4-Gln5-Gln6-Phe7-Phe8-Gly9-Leu10-Met11-NH2, in ethanol. At elevated solution temperatures (55 to 75 °C), several reactions are observed, including a protonation event, i.e., [subP+2H]2+ + H+ → [subP+3H]3+, that appears to be regulated by a configurational change and two sequential bond cleavages (the Pro2-Lys3 peptide bond is cleaved to form the smaller nonapeptide Lys3-Met11-NH2 [subP(3-11)], and subsequently, subP(3-11) is cleaved at the Pro4-Gln5 peptide bond to yield the heptapeptide Gln5-Met11-NH2 [subP(5-11)]). Each of the product peptides [subP(3-11) and subP(5-11)] is accompanied by a complementary diketopiperazine (DKP): cyclo-Arg1-Pro2 (cRP) for the first cleavage, and cyclo-Lys3-Pro4 (cKP) for the second. Insight about the mechanism of degradation is obtained by comparing kinetics calculations of trial model mechanisms with experimental data. The best model of our experimental data indicates that the initial cleavage of subP is regulated by a conformational change, likely a trans→cis isomerization of the Arg1-Pro2 peptide bond. The subP(3-11) product has a long lifetime (t1/2 ~ 30 h at 55 °C) and appears to transition through several structural intermediates prior to dissociation, suggesting that subP(3-11) is initially formed with a Lys3-trans-Pro4 peptide bond configuration and that slow trans→cis isomerization regulates the second bond cleavage event as well. From these data and our model mechanisms, we obtain transition state thermochemistry ranging from ΔH‡ = 41 to 85 kJ mol-1 and ΔS‡ = - 43 to - 157 J mol-1 K-1 for each step in the reaction. Graphical Abstract.

The Role of Substance P in Secondary Pathophysiology after Traumatic Brain Injury

It has recently been shown that substance P (SP) plays a major role in the secondary injury process following traumatic brain injury (TBI), particularly with respect to neuroinflammation, increased blood–brain barrier (BBB) permeability, and edema formation. Edema formation is associated with the development of increased intracranial pressure (ICP) that has been widely associated with increased mortality and morbidity after neurotrauma. However, a pharmacological intervention to specifically reduce ICP is yet to be developed, with current interventions limited to osmotic therapy rather than addressing the cause of increased ICP. Given that previous publications have shown that SP, NK1 receptor antagonists reduce edema after TBI, more recent studies have examined whether these compounds might also reduce ICP and improve brain oxygenation after TBI. We discuss the results of these studies, which demonstrate that NK1 antagonists reduce posttraumatic ICP to near normal levels within 4 h of drug administration, as well as restoring brain oxygenation to near normal levels in the same time frame. The improvements in these parameters occurred in association with an improvement in BBB integrity to serum proteins, suggesting that SP-mediated increases in vascular permeability significantly contribute to the development of increased ICP after acute brain injury. NK1 antagonists may therefore provide a novel, mechanistically targeted approach to the management of increased ICP.

Proteolysis controls endogenous substance P levels

Substance P (SP) is a prototypical neuropeptide with roles in pain and inflammation. Numerous mechanisms regulate endogenous SP levels, including the differential expression of SP mRNA and the controlled secretion of SP from neurons. Proteolysis has long been suspected to regulate extracellular SP concentrations but data in support of this hypothesis is scarce. Here, we provide evidence that proteolysis controls SP levels in the spinal cord. Using peptidomics to detect and quantify endogenous SP fragments, we identify the primary SP cleavage site as the C-terminal side of the ninth residue of SP. If blocking this pathway increases SP levels, then proteolysis controls SP concentration. We performed a targeted chemical screen using spinal cord lysates as a proxy for the endogenous metabolic environment and identified GM6001 (galardin, ilomastat) as a potent inhibitor of the SP _1–9-producing activity present in the tissue. Administration of GM6001 to mice results in a greater-than-three-fold increase in the spinal cord levels of SP, which validates the hypothesis that proteolysis controls physiological SP levels.

The role of substance p in ischaemic brain injury

Stroke is a leading cause of death, disability and dementia worldwide. Despite extensive pre-clinical investigation, few therapeutic treatment options are available to patients, meaning that death, severe disability and the requirement for long-term rehabilitation are common outcomes. Cell loss and tissue injury following stroke occurs through a number of diverse secondary injury pathways, whose delayed nature provides an opportunity for pharmacological intervention. Amongst these secondary injury factors, increased blood-brain barrier permeability and cerebral oedema are well-documented complications of cerebral ischaemia, whose severity has been shown to be associated with final outcome. Whilst the mechanisms of increased blood-brain barrier permeability and cerebral oedema are largely unknown, recent evidence suggests that the neuropeptide substance P (SP) plays a central role. The aim of this review is to examine the role of SP in ischaemic stroke and report on the potential utility of NK1 tachykinin receptor antagonists as therapeutic agents.

Identification of N-glycosylation in prolyl endoprotease from Aspergillus niger and evaluation of the enzyme for its possible application in proteomics

An acidic prolyl endoprotease from Aspergillus niger was isolated from the commercial product Brewers Clarex to evaluate its possible application in proteomics. The chromatographic purification yielded a single protein band in sodium dodecyl sulfate polyacrylamide gel electrophoresis providing an apparent molecular mass of 63 kDa and a broad peak (m/z 58,061) in linear matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) indicating the glycoprotein nature of the enzyme. Indeed, a colorimetric assessment with phenol and sulfuric acid showed the presence of neutral sugars (9% of weight). The subsequent treatment with N-glycosidase F released a variety of high-mannose type N-glycans, which were successfully detected using MALDI-TOF MS. MALDI-TOF/TOF tandem MS analysis of glycopeptides from a tryptic digest of prolyl endoprotease unraveled the identity of the N-glycosylation site in the primary structure. The data obtained also show that the enzyme is present in its processed form, i.e. without putative signal and propeptide parts. Spectrophotometric measurements demonstrated optimal activity at pH 4.0-4.5 and also high thermostability for the cleavage at the C-terminal part of proline residues. In-solution digestion of standard proteins (12-200 kDa) allowed to evaluate the cleavage specificity. The enzyme acts upon proline and alanine residues, but there is an additional minor cleavage at some other residues like Gly, Leu, Arg, Ser and Tyr. The digestion of a honeybee peptide comprising six proline residues (apidaecin 1A) led to the detection of specific peptides terminated by proline as it was confirmed by MALDI postsource decay analysis.

Detection of stable N-terminal protachykinin A immunoreactivity in human plasma and cerebrospinal fluid

Substance P (SP) is a neuropeptide that is released from sensory nerves and several types of immune cells. It is involved in the transmission of pain and has a number of pro-inflammatory effects. Like other neuropeptides, SP is derived from a large precursor peptide, protachykinin A (PTA). Alternative splicing results in the production of four distinct PTA molecules that all contain the sequence of SP and a common N-terminal region consisting of 37 amino acids. We have developed a sandwich immunoassay using antibodies against the N-terminal part of PTA. Here we demonstrate that N-terminal PTA immunoreactivity is present in human circulation and cerebrospinal fluid (CSF). The concentration was about 90 times higher in CSF than in EDTA-plasma. Analytical reversed phase HPLC revealed that NT-PTA 1-37 is the main immunoreactivity in human circulation and CSF. Moreover, compared to the low in vitro stability of SP of less than 12 min, NT-PTA immunoreactivity is absolutely stable in EDTA-plasma and CSF for more than 48 h. As NT-PTA 1-37 is produced in stoichiometric amounts and is theoretically co-released with SP, we suggest the measurement of NT-PTA immunoreactivity as surrogate molecule for the release of bioactive SP.

Enzymic inactivation of substance P in the central nervous system

A membrane-bound 'substance P degrading enzyme' (EC 3.4.24.-) from human brain has been purified to apparent homogeneity. The enzyme was extracted from a membrane fraction of human diencephalon with a non-ionic detergent, Brij 35, and activity was monitored by measuring the rate of disappearance of added substance P using radioimmunoassay, bioassay or radiochemical assay. The enzyme is a thermolabile, neutral metallo-endopeptidase with a relative molecular mass of about 50000. It cleaves substance P between Gln6-Phe7, Phe7-Phe8 and Phe8-Gly9, with a ratio of 0.7:1:1. The breakdown products have been identified by a combination of reverse-phase high-performance liquid chromatography and amino acid analysis. A similar cleavage pattern of substance P has also been demonstrated in a synaptic membrane fraction prepared from rat brain, indicating that a 'substance P-degrading enzyme' is the major peptidase responsible for inactivating the peptide in rat brain membranes. The properties of this enzyme distinguished it from previously described peptidases for which substance P is a substrate. Its high selectivity and its affinity for substance P, among many other neuropeptides, suggest that it may be involved in the physiological inactivation of the peptide by neural tissues.

Sulfated chitooligosaccharides as prolyl endopeptidase inhibitor

Prolyl endopeptidase (PEP, EC 3.4.21.26) is a proline-specific endopeptidase with a serine-type mechanism, which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. PEP has been involved in neurodegenerative disorders, therefore, the discovery of PEP inhibitors can revert memory loss caused by amnesic compounds. In this study, we prepared hetero-chitooligosaccharides (COSs) with different molecular sizes using ultrafiltration (UF) membrane reactor system from hetero-chitosan with different degrees of deacetylation (DD; 90%, 75% and 50% deacetylation), and synthesized sulfated COSs (SCOSs). PEP inhibitory activities of SCOSs were evaluated and the results showed that 50% deacetylated SCOSs (50-SCOSs) exhibited higher inhibitory activities than those of 90% and 75% deacetylated SCOSs (90-SCOSs and 75-SCOSs). Among the 50-SCOSs (50-SCOS I, 5000-10,000Da; 50-SCOS II, 1000-5000Da; 50-SCOS III, below 1000Da), 50-SCOS II possessed the highest inhibitory activity and IC(50) value was 0.38mg/ml. Kinetics studies with 50-SCOS II indicated a competitive enzyme inhibition with a K(i) value of 0.78mg/ml. It was concluded that the 50-SCOS II may be useful for PEP inhibitor and for developing a new type PEP inhibitor from carbohydrate based materials.

Substance P in traumatic brain injury

Recent evidence has suggested that neuropeptides, and in particular substance P (SP), may play a critical role in the development of morphological injury and functional deficits following acute insults to the brain. Few studies, however, have examined the role of SP, and more generally, neurogenic inflammation, in the pathophysiology of traumatic brain injury and stroke. Those studies that have been reported suggest that SP is released following injury to the CNS and facilitates the increased permeability of the blood brain barrier, the development of vasogenic edema and the subsequent cell death and functional deficits that are associated with these events. Inhibition of the SP activity, either through inhibition of the neuropeptide release or the use of SP receptor antagonists, have consistently resulted in profound decreases in edema formation and marked improvements in functional outcome. The current review summarizes the role of SP in acute brain injury, focussing on its properties as a neurotransmitter and the potential for SP to adversely affect outcome.

Investigation of the metabolism of substance P at the blood-brain barrier using LC-MS/MS

Substance P (SP) has been associated with pain and depression as well as neurodegenerative diseases. Many of these diverse actions of SP can potentially be attributed to SP metabolites generated at the blood-brain barrier (BBB). In this study, the metabolism of SP was investigated using an in vitro model of the BBB and LC-MS/MS. Substance P metabolism was found to be non-saturable in the concentration range of 100 nM to 10 microM, with approximately 70% of the peptide remaining intact after 5 h. The major metabolites of SP were identified by MS as 3-11 and 5-11. Two previously unreported metabolites, 5-11 and 6-11, were also found in our studies. Several additional minor SP metabolites, including 1-9 and 2-11, were also identified. A profile of the SP metabolites generated by the BBB over time was obtained. The results from the present study provide a better understanding of the role of the blood-brain barrier in the pharmacology of SP.

In vivo metabolism and clearance of substance P and co-expressed tachykinins in rat striatum

Neurons expressing the preprotachykinin A gene, which encodes the sequences of substance P, neurokinin A, neuropeptide gamma and neuropeptide K, exemplify peptide co-existence. Furthermore, there is also evidence that substance P fragments have biological activity. However, the relative contribution of each of these peptides to tachykinin signalling is still poorly understood. An important factor which will determine the characteristics of the signal mediated by co-localised peptides is their clearance from the extracellular space. The striatum, in which tachykinins are present and exert neuromodulatory roles, can be used as a model to investigate this aspect. Therefore, in this study we characterised in vivo in the striatum the metabolism and clearance of substance P and of the other three co-expressed peptides. After intrastriatal administration of 1 pmol, tritiated substance P disappeared too rapidly for metabolites to be detected. However, when 10 nmol substance P and 1 pmol tritiated substance P were co-injected, substance P(1-4) and substance P(1-7), which are biologically active, were detected as major metabolites. Under these conditions, the rate of decay of tritiated substance P was 0.2 nmol/min. The effects of the peptidase inhibitors thiorphan, bestatin and captopril suggested that neutral endopeptidase 24.11 and aminopeptidases were involved in primary substance P cleavages, whereas angiotensin-converting enzyme was involved in secondary cleavages. The monitoring of the decay of unlabelled substance P by high-performance liquid chromatography gave a rate of 0.16 nmol/min. Using high-performance liquid chromatography with capillary electrophoresis, the rates of decay of 10 nmol neurokinin A or neuropeptide gamma were five and seven times faster than that of substance P. In contrast, over the time course of the experiment, no significant decay of neuropeptide K was detected. These results show that substance P disappears rapidly from the extracellular space, and supports the formation in vivo of major N-terminal active substance P metabolites. Our study also highlights significant differences in the clearance of co-expressed tachykinins and suggests that certain species may disappear relatively slowly from the extracellular space, and thus may make a significant temporal and spatial contribution to signalling.

Investigation of the metabolism of substance P at the blood-brain barrier using capillary electrophoresis with laser-induced fluorescence detection

Substance P (SP) metabolism was investigated upon exposure to a monolayer of bovine brain microvessel endothelial cells (BBMECs), a cell culture model of the blood-brain barrier. SP was incubated with the BBMECs and its metabolism was followed as a function of time over a 5-h period. The resulting samples were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated, and detected using cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Upon exposure to the BBMEC monolayer, SP rapidly degraded to produce the N-terminal (1-9), (1-4) and (1-7) and C-terminal (2-11) and (3-11) fragments. These results were compared with those in an earlier report from our laboratory, where SP metabolism was investigated in vivo by microdialysis sampling in rat striatum.

Investigation of the metabolism of substance P in rat striatum by microdialysis sampling and capillary electrophoresis with laser-induced fluorescence detection

The metabolism of substance P (SP) was investigated in rat striatum using in vivo microdialysis. Substance P was perfused for 5 h at 0.2 microl/min, and its metabolism was followed for over 13 h. The resulting samples were derivatized precolumn with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated and detected by cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Substance P rapidly degraded to form the fragments (3-11), (1-9), (1-4) and, to a lesser extent, (1-7). The metabolites reached steady-state levels 2-3 h after addition of SP.

Kinetic and mechanistic studies of prolyl oligopeptidase from the hyperthermophile Pyrococcus furiosus

Prolyl oligopeptidase (POP) is widely distributed in mammals, where it is implicated in neuropeptide processing. It is also present in some bacteria and archaea. Because POP is found in mesophilic and hyperthermophilic organisms, and is distributed among all three phylogenetic domains, studies of its function and structure could lead to new insights about the evolution of enzyme mechanisms and thermostability. Kinetic studies were conducted on the POP of the hyperthermophilic archaeon Pyrococcus furiosus (Pfu) 85 degrees C in both H(2)O and D(2)O. Pfu POP displayed many similarities to mammalian POPs, however the solvent isotope effect (k(0)/k(1)) was 2.2 at both high and low pH, indicating that general base/acid catalysis is the rate-limiting step. The pH-rate profiles indicated a three-deprotonation process with pK(a) values of 4.3, 7.2, and 9.1. The temperature dependence of these values revealed a heat of ionization of 4.7 kJ/mol for pK(es1) and 22 kJ/mol for pK(es2), suggesting the catalytic involvement of a carboxyl group and an imidazole group, respectively. Temperature dependence of the catalytic rate was assessed at pH 6.0 and 7.6. Entropy values of -119 and -143 Jmol(-1)K(-1) were calculated at the respective pH values, with a corresponding difference in enthalpy of 8.5 kJ/mol. These values suggest that two or three hydrogen bonds are broken during the transition state of the acidic enzyme form, whereas only one or two are broken during the transition state of the basic enzyme form. A model has been constructed for Pfu POP based on the crystal structure of porcine POP and the sequence alignment. The similarities demonstrated for POPs from these two organisms reflect the most highly conserved characteristics of this class of serine protease, whereas the differences between these enzymes highlights the large evolutionary distance between them. Such fundamental information is crucial to our understanding of the function of proteins at high temperature.

Sialogogic activity in the rat of peptides analogous to [Tyr8]-substance P in which substitutions have been made in the N-terminal amino acids

In order to elucidate the regulatory roles for salivation of amino acids in positions 1-4 of the N-terminal region of [Tyr8]-substance P (SP), the structure-sialogogic activity correlations of various synthetic octa- to undecapeptides replaced in positions 1-4 of [Tyr8]-SP with each of 19 common amino acids, one by one, and with the same sequence of the C-terminal hepatapeptide as that of [Tyr8]-SP, were studied in the submandibular glands of rats after intraperitoneal injection. Each of 19 octa-, nona-, deca- and undecapeptides with replaced amino acids and a penta- to decapeptide with the progressive elimination of the N-terminal portion were newly synthesized by the multipin peptide method. All octa- to undecapeptides replaced with each of 19 common amino acids in positions 1-4 had sialogogic activities. In 19 octa- and decapeptides in which P4 and P2 had been replaced, four and three replacements, respectively, had significantly increased secretory activities. In contrast, in 19 nonapeptides in which K3 had been replaced, none had significantly increased secretory activities. Furthermore, in 19 undecapeptides in which R1 had been replaced, most replacements had significantly increased or equipotent activities for fluid secretion. It is concluded that amino acids in the N-terminal region of various tachykinins may not need to be strictly conserved and that amino acid residues in the N-terminal portion, R1 in particular and P2, may strongly inhibit secretory activity.

HIV-1 protease inhibition and anti-HIV effect of natural and synthetic water-soluble lignin-like substances

Water-soluble lignin extracted from natural sources and dehydrogenated polymers of p-coumaric acid and ferulic acid inhibited HIV-1 protease activity. The dehydrogenated polymers, which are thought to be model compounds for lignin, were synthesized and fractionated into four ranges of molecular mass by ultra-filtration: i.e., over 30 kDa, 30-10 kDa, 10-1 kDa and 1 kDa-500 Da. All of these fractions had HIV-1 protease inhibitory activity. The anti-HIV-1 effect of the smallest mass fractions of the dehydrogenated polymers (1 kDa-500 Da) was also tested, and it was found that these fractions inhibited the replication of HIV-1 in MT-4 cells.

Enzymatic degradation of neuropeptide FF and SQA-neuropeptide FF in the mouse brain

Degradation of neuropeptide FF (NPFF) and SQA-neuropeptide FF (SQA-NPFF) by mouse brain sections was investigated by using capillary electrophoresis with UV detection for the separation and the identification of the degradation products. The half disappearance time of SQA-NPFF was 2-fold greater than that of NPFF. NPFF was cleaved preferentially into an inactive metabolite, Gln-Arg-Phe-NH2, in the cerebrum slices. SQA-NPFF was hydrolyzed by an unidentified degrading activity to generate NPFF, and NPFF accounted for a larger part of SQA-NPFF degradation in the hindbrain and cervical spinal cord than in the cerebrum slices. These findings suggest that, depending on the brain regions, NPFF produced from SQA-NPFF could prolong the biologic effects of SQA-NPFF.

Substance P fragments and striatal endogenous dopamine outflow: interaction with substance P

Accumulating evidence shows that N- and C-terminal substance P fragments have significant biological activity. Substance P(1-9) and substance P(6-11) have been reported to be major substance P metabolites in rat striatum. We investigated the effects of these fragments on endogenous dopamine outflow in rat striatal slices. Substance P-(1-9) and substance P-(6-11) induced a significant increase in dopamine outflow at 0.1 and 1 nM. The effects of substance P-(6-11) (1 nM) were reversed by the tachykinin NK1 antagonist WIN 51,708 (17beta-hydroxy-17alpha-ethynyl-5alpha-androstano[3,2- b]pyrimido[1,2-a]benzimidazole) (2.5 nM), whereas the effects of substance P-(1-9) were not modified by the antagonist. Substance P-(1-9) and substance P-(6-11) (1 nM) did not increase the dopamine overflow induced by 25 mM KCI. The effects of the two fragments were reversed by the muscarinic antagonist atropine (1 microM) but not by nicotinic antagonists dihydro-beta-erythroidine (0.5 microM) and pempidine (10 microM). The co-incubation of tissue with substance P and each fragment in a 1/1 or 10/1 ratio of substance P to metabolite revealed a negative interaction between parent and fragments. A similar pattern was observed when substance P was co-administered with the active fragments substance P(1-4), substance P(1-7), substance P(5-11) and substance P(8-11). The data show that substance P-(1-9) and substance P-(6-11) have modulatory effects similar to substance P. However, the presence of active substance P metabolites does not appear to amplify the signal mediated by the parent peptide.

Inhibition of HIV-1 protease by water-soluble lignin-like substance from an edible mushroom, Fuscoporia obliqua

Activity that inhibited protease of human immunodeficiency virus type 1 was found in boiling water extracts of an edible mushroom, Fuscoporia obliqua. The active component was identified as a water-soluble lignin derivative of high molecular weight. Other polyphenols of low molecular weight and monomeric components of lignin did not inhibit the protease.

Application of [(125)I]-[Tyr8]-substance P prepared by the chloramine-T method to receptor-binding experiments after subsequent reduction with mercaptoethanol and purification by reversed-phase liquid chromatography

Radiolabeling of [Tyr8]-substance P ([Tyr8]-SP) with the (125)I-isotope was performed by use of the chloramine-T technique. The primary formed radiolabeled product, having been quantitatively converted to the corresponding sulfoxide yielding [(125)I]-[Tyr8]-(Met11-->O)-SP completely lacked any binding to proteins rich in SP receptor populations. However, after reductive treatment with mercaptoethanol for about 2 h, a complete reconstitution of the Met11 thioether structure was observed. The reduced peptide, consisting of [(125)I]-[Tyr8]-(Met11)-SP was separated from its by-products by reversed-phase high-performance liquid chromatography on octadecylsilyl silica gel with 100 mM triethyl ammonium formate buffer containing 22% acetonitrile (pH 2.2). The labeled SP derivative prepared by this two-step synthesis was obtained in 73% overall yield related to the [Tyr8]-SP starting material and exhibited a specific activity of 1.9-10(6) Ci/M. In contrast to [(125)I]-[Tyr8]-->(Met11-->O)-SP, satisfactory receptor-binding was now observed with the [(125)I]-->[Tyr8]-(Met11)-SP derivative.

Evaluation of capillary electrophoresis with post-column derivatization and laser-induced fluorescence detection for the determination of substance P and its metabolites

A method for the detection of substance P and its metabolites using capillary electrophoresis with post-capillary derivatization and laser-induced fluorescence detection is described. The post-capillary chemical derivatization system employs naphthalene-2,3-dicarboxaldehyde and beta-mercaptoethanol. Two reactor designs were evaluated for the determination of substance P and its metabolites. The fluorescent spectroscopic properties of the derivatives under optimal separation conditions were also examined. The final system was evaluated for the investigation of substance P metabolism in brain following perfusion of the striatum with substance P using microdialysis sampling.

Purification and characterization of substance P endopeptidase activities in the rat spinal cord

Two enzymes with substance P degrading activity were purified from the membrane bound fraction of the rat spinal cord. The purified enzymes were characterized with regard to biochemical and kinetic properties. One of the enzymes exhibited close similarity to neutral endopeptidase 24.11 (NEP, EC 3.4.24.11), while the other resembled a substance P converting endopeptidase (SPE), which has previously been identified and purified from human cerebrospinal fluid (CSF). Detergent treated spinal cord homogenates from male Sprague Dawley rats were purified by anion-exchange chromatography (DEAE-sepharose CL-6B), hydrophobic-interaction chromatography (phenyl-sepharose CL-4B) and molecular sieving (Sephadex G-50). Two fractions with enzymes differing in size were recovered and allowed for further purification to apparent homogeneity by ion-exchange chromatography and molecular sieving on a micro-purification system (SMART). The enzyme activities were monitored by following the conversion of synthetic substance P using a radioimmunoassay specific for the heptapeptide product, substance P (1-7). By SDS-polyacrylamide gel electrophoresis of the purified enzymes molecular weights of 43 and 70 kDa were estimated for the SPE-like and NEP-like activity, respectively. A K(m) of 5 microM was determined for the conversion of substance P to its (1-7) fragment by the SPE-like activity. Reversed-phase HPLC together with mass spectrometry permitted identification of all fragments released from substance P by the peptidases. The released fragments were for both enzymes identified as substance P (1-7), substance P (8-11), substance P (1-8), substance P (9-11). The NEP-like enzyme preparation also gave substance P (1-6) as a major product.

N- and C-terminal substance P fragments modulate striatal dopamine outflow through a cholinergic link mediated by muscarinic receptors

The present study investigated whether the modulatory effects of substance P and substance P fragments on striatal dopamine release involve a cholinergic link. Rat striatal slices were incubated with substance P, substance P(1-4), substance P(1-7), substance P(5-11) and substance P(8-11) in the absence or presence of various agents which modify cholinergic transmissions, and endogenous dopamine outflow was measured using high-performance liquid chromatography. The incubation of striatal slices with substance P and its N- and C-terminal fragments (1 nM) induced a significant overflow of endogenous dopamine. Neostigmine (150 nM) potentiated the effects of substance P and its fragments, whereas the incubation with hemicholinium-3 (50 microM) abolished the effects of the peptides on dopamine outflow. The acetylcholinesterase inhibitor and the inhibitor of choline uptake did not have intrinsic effects on dopamine outflow. The muscarinic antagonist atropine (1 microM) reversed completely the effects of substance P and its fragments, whereas the nicotinic antagonists dihydro-beta-erythroidine (0.5 microM) and pempidine (10 microM) were devoid of effects. None of the cholinergic antagonists modified dopamine outflow. The results suggest that substance P and several N- and C-terminal substance P fragments activate cholinergic neurons in striatal slices. The released acetylcholine induces an increased dopamine outflow, mediated by muscarinic receptors. These observations represent additional evidence which supports the functional interactions between substance P, acetylcholine and dopamine in the striatum. Furthermore, they show that substance P fragments may exert neuromodulatory effects through mechanisms similar to those underlying the effects of the parent peptide.

Tachykinins: receptor to effector

Tachykinins belong to an evolutionarily conserved family of peptide neurotransmitters. The mammalian tachykinins include substance P, neurokinin A and neurokinin B, which exert their effects by binding to specific receptors. These tachykinin receptors are divided into three types, designated NK1, NK2 and NK3, respectively. Tachykinin receptors have been cloned and contain seven segments spanning the cell membrane, indicating their inclusion in the G-protein-linked receptor family. The continued development of selective agonists and antagonists for each receptor has helped elucidate roles for these mediators, ranging from effects in the central nervous system to the perpetuation of the inflammatory response in the periphery. Various selective ligands have shown both inter- and intraspecies differences in binding potencies, indicating distinct binding sites in the tachykinin receptor. The interaction of tachykinin with its receptor activates Gq, which in turn activates phospholipase C to break down phosphatidyl inositol bisphosphate into inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 acts on specific receptors in the sarcoplasmic reticulum to release intracellular stores of Ca2+, while DAG acts via protein kinase C to open L-type calcium channels in the plasma membrane. The rise in intracellular [Ca2+] induces the tissue response. With an array of actions as diverse as that seen with tachykinins, there is scope for numerous therapeutic possibilities. With the development of potent, selective non-peptide antagonists, there could be potential benefits in the treatment of a variety of clinical conditions, including chronic pain, Parkinson's disease, Alzheimer's disease, depression, rheumatoid arthritis, irritable bowel syndrome and asthma.

Evidence for modulatory effects of substance P fragments (1-4) and (8-11) on endogenous dopamine outflow in rat striatal slices

The effects of substance P-(1-4) and substance P-(8-11) on endogenous dopamine outflow in rat striatal slices were investigated. The dose-response curves (0.01 nM to 1 microM) were bell-shaped for both peptides, with significant increases in dopamine outflow at 0.1 and 1 nM. Dopamine overflow elicited by 1 nM substance P-(1-4) or substance P-(8-11) and 25 mM KCl was additive. Although substance P-(8-11) contains a truncated tachykinin sequence, the tachykinin NK1 receptor antagonist WIN 51,708 (17 beta-hydroxy-17 alpha-ethynyl-5 alpha-androstano[3,2-b]pyrimido[1,2- a]benzimidazole (2.5 nM) fully reversed its effect. The interaction between the antagonist and 1 nM substance P-(1-4) was statistically not significant. The data constitute the first evidence that the fragments substance P-(1-4) and substance P-(8-11) could exert central effects and suggest that they may play a role in neuromodulation in the basal ganglia.

Substance P-(1-7) and substance P-(5-11) locally modulate dopamine release in rat striatum

The effects of substance P, substance P-(1-7) and substance P-(5-11) on endogenous dopamine outflow in rat striatal slices were investigated. The dose-response curves (0.01 nM to 10 microM) were bell-shaped, with significant increases at 0.1 and 1 nM but with no effect at higher concentrations. The tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P, significantly increased dopamine outflow at 10 and 100 nM. The effects of substance P or substance P-(5-11) and 25 mM KCl were additive. A negative interaction was observed with substance P-(1-7) and K+. The increase in dopamine outflow elicited by 1 nM substance P and substance P-(5-11) was reversed by the tachykinin NK1 receptor antagonist WIN 51,708 (17 beta-hydroxy-17 alpha-ethynyl-5 alpha-androstano[3,2-b]pyrimido[1,2- alpha]benzimidazole) (25 and 250 nM), whereas only partial reversal was observed for the effect of substance P-(1-7). These results show that substance P fragments locally modulate striatal dopamine outflow and the mechanisms underlying this modulation may differ between N- and C-terminal fragments.

Sample preparation, high-performance liquid chromatographic separation and determination of substance P-related peptides

This review deals with the determination of low levels of substance P and peptide fragments derived from the undecapeptide, i.e. covers the whole amount of so-called substance P-like immunoreactivity (SPLI) in biological samples. First an overview of the most currently used sample pretreatment procedures is given, followed by a description of the most effective high-performance liquid chromatographic (HPLC) separation methods. Special attention is paid to the choice of the appropriate column and the possible pitfalls encountered in separation of fmol amounts of peptide material. Subsequently the most important techniques of detection are discussed. This section primarily focuses on the coupling of HPLC with radioimmunoassay (RIA), which is indispensable for detection of components in the fmol range at present. Finally, some aspects of preparation and chromatographic separation of radiolabelled antigens for use in RIA are discussed.

An endo-acting proline-specific oligopeptidase from Treponema denticola ATCC 35405: evidence of hydrolysis of human bioactive peptides

An endo-acting proline-specific oligopeptidase (prolyl oligopeptidase [POPase], EC 3.4.21.26) was purified to homogeneity from the Triton X-100 extracts of cells of Treponema denticola ATCC 35405 (a human oral spirochete) by a procedure that comprised five successive fast protein liquid chromatography steps. The POPase is a cell-associated 75- to 77-kDa protein with an isoelectric point of ca. 6.5. The enzyme hydrolyzed (optimum pH 6.5) the Pro-pNA bond in carbobenzoxy-Gly-Pro-p-nitroanilide (Z-Gly-Pro-pNA) and bonds at the carboxyl side of proline in several human bioactive peptides, such as bradykinin, substance P, neurotensin, angiotensins, oxytocin, vasopressin, and human endothelin fragment 22-38. The minimum hydrolyzable peptide size was tetrapeptide P3P2P1P'1, while the maximum substrate size was ca. 3 kDa. An imino acid residue in position P1 was absolutely necessary. The hydrolysis of Z-Gly-Pro-pNA was potently inhibited by the following, with the Ki(app) (in micromolar) in parentheses: insulin B-chain (0.7), human endothelin-1 (0.5), neuropeptide Y (1.7), substance P (32.0), T-kinin (4.0), neurotensin (5.0), and bradykinin (16.0). Chemical modification and inhibition studies suggest that the POPase is a serine endopeptidase whose activity depends on the catalytic triad of COOH ... Ser ... His but not on a metal. The amino acid sequence around the putative active-site serine is Gly-Gly-Ser-Asn-Pro-Gly. The enzyme is suggested to contain a reactive cysteinyl residue near the active site. Amino acid residues 4 to 24 of the first 24 N-terminal residues showed a homology of 71% with the POPase precursor from Flavobacterium meningosepticum and considerable homology with the Aeromonas hydrophila POPase. The ready hydrolysis of human bioactive peptides at bonds involving an imino acid residue suggests that enzymes like POPase may contribute to the chronicity of periodontal infections by participating in the peptidolytic processing of those peptides.

Purification and characterization of prolyl endopeptidase from rat skin

An enzyme with the specificity of a prolyl endopeptidase was purified approximately 329-fold from rat skin. The enzyme has a molecular weight of 70,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a pH optimum of 5.8 as checked with 7-(Succinyl-Gly-Pro)-4- methylcoumarinamide (Suc-Gly-Pro-MCA) as the substrate. The optimal temperature for the enzyme activity was 40 degrees C. The Km and Vmax values for Suc-Gly-Pro-MCA were 0.7 mM and 68 nmol/min per mg protein, respectively. The enzyme activity was markedly inhibited by diisopropyl fluorophosphate, p-chloromercuribenzoic acid, N-ethylmaleimide, Zn2+ and Cu2+, while it was partially inhibited by phenylmethanesulphonyl fluoride. The purified enzyme was shown to release the N-terminal tetrapeptide, Arg-Pro-Lys-Pro, from substance P producing the C-terminal heptapeptide, Gln-Gln-Phe-Phe-Gly-Met- CONH2. In the skin, this enzyme might be related to the inactivation of substance P.

Cloning of proline-specific endopeptidase gene from Flavobacterium meningosepticum: expression in Escherichia coli and purification of the heterologous protein

Proline-specific endopeptidase (PSE) (EC 3.4.21.26) from Flavobacterium meningosepticum was subjected to partial amino acid sequencing. According to the peptide sequences obtained, oligonucleotides were used to amplify a PSE-specific DNA fragment of 930 bp from F. meningosepticum genomic DNA, employing the polymerase chain reaction technique. This fragment served as a molecular probe to isolate the respective gene. DNA sequencing revealed that the PSE gene consists of 2118 bp coding for a 78,634 Da protein of 705 amino acids. The coding region was cloned in different expression vectors of Escherichia coli. Transformed E. coli cells overproduce an active prolyl endopeptidase of 75,000 relative molecular mass, which is delivered to the bacterial periplasmic space. Up to 1.6 units of active prolyl endopeptidase were obtained from 1 mg E. coli cells. Furthermore, the efficient purification of active prolyl endopeptidase from the periplasm of recombinant E. coli cells is described.

Tachykinin receptors: a radioligand binding perspective

The last decade has witnessed major breakthroughs in the study of tachykinin receptors. The currently described NK-1, NK-2, and NK-3 receptors have been sequenced and cloned from various mammalian sources. A far greater variety of tachykinin analogues are now available for use as selective agonists and antagonists. Importantly, potent nonpeptide antagonists highly selective for the NK-1 and NK-2 receptors have been developed recently. These improved tools for tachykinin receptor characterization have enabled us to describe at least three distinct receptor types. Furthermore, novel antagonists have yielded radioligand binding and functional data strongly favoring the existence of putative subtypes of NK-1 and especially NK-2 receptors. Whether these subtypes are species variants or true within-species subtypes awaits further evidence. As yet undiscovered mammalian tachykinins, or bioactive fragments, may have superior potency at a specific receptor class. The common C terminus of tachykinins permits varying degrees of interaction at essentially all tachykinin receptors. Although the exact physiological significance of this inherent capacity for receptor "cross talk" remains unknown, one implication is for multiple endogenous ligands at a single receptor. For example, NP gamma and NPK appear to be the preferred agonists and binding competitors at some NK-2 receptors, previously thought of as exclusively "NKA-preferring." Current evidence suggests that tachykinin coexistence and expression of multiple receptors may also occur with postulated NK-2 and NK-1 receptor subtypes. Other "tachykinin" receptors may recognize preprotachykinins and the N terminus of SP. In light of these recent developments, the convenient working hypothesis of three endogenous ligands (SP, NKA, and NKB) for three basic receptor types (NK-1, NK-2, and NK-3) may be too simplistic and in need of amendment as future developments occur (Burcher et al., 1991b). In retrospect, the 1980s contributed greatly to our understanding of the structure, function, and regulation of tachykinins and their various receptors. The development of improved, receptor subtype-selective antagonists and radioligands, in addition to recent advances in molecular biological techniques, may lead to a more conclusive pharmacological and biochemical characterization of tachykinin receptors. The 1990s may prove to be the decade of application, where a better understanding of the roles played by endogenous tachykinins (at various receptor subtypes) under pathophysiological conditions will no doubt hasten the realization of clinically useful therapeutic agents.

Recovery of substance P and related C-terminal fragments on solid-phase extraction cartridges for subsequent high-performance liquid chromatographic separation and radioimmunoassay

The recoveries of substance P (SP) and five related peptides were evaluated on different types of solid-phase extraction sorbent. Best results were obtained by use of a C18 silica gel cartridge. Marked differences of extraction yields occurred for the different peptide fragments and, in general, recovery increased with increasing hydrophobicity of the peptide when reversed-phase materials like C18 and C8 cartridges were used. This observation is indicative of a sorption-desorption mechanism by prevailing solvophobic interactions. A similar trend was found when phenylpropyl silica gel (CPhenyl), generally known as a reversed-phase adsorbent of lower hydrophobicity, was used. It was concluded that a substantial participation of analyte-matrix pi-pi interactions has to be taken into account when extraction yields are compared with corresponding values obtained by use of a C8 cartridge. With CN silica gel cartridges, marked differences in extraction yields were obtained by use of acetonitrile or methanol as the organic modifier. As an attempt to explain this observation, conformational effects were assumed for the sorption-desorption behaviour of the peptides on the polar matrix.

A comparison of the properties and enzymatic activities of three angiotensin processing enzymes: angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11

The discovery of angiotensin-(1-7) [Ang-(1-7)] as a bioactive Ang II fragment of the renin-angiotensin system (RAS) alters the current understanding of the enzymatic components that comprise the RAS cascade. Two neutral endopeptidases, prolyl endopeptidase (E.C. 3.4.21.26) and neutral endopeptidase 24.11 (E.C. 3.4.24.11), are capable of forming Ang-(1-7) from Ang I and have been implicated in the in vivo processing of Ang I. This makes them putative Ang processing enzymes and part of the RAS cascade. This review summarizes the physical characteristics and distribution of angiotensin converting enzyme (E.C. 3.4.15.1), a known Ang I processing enzyme, and compares its features to what is known of prolyl endopeptidase and neutral endopeptidase 24.11.

Y-29794--a non-peptide prolyl endopeptidase inhibitor that can penetrate into the brain

A novel non-peptide prolyl endopeptidase (PPCE) inhibitor, Y-29794, has been identified. Y-29794 selectively and competitively inhibited rat brain PPCE (Ki = 0.95 nM) in a reversible manner. Ex vivo study demonstrated that Y-29794 could penetrate into brain to exhibit dose-dependent and long-lasting inhibition. Furthermore, Y-29794 was found to potentiate the effect of TRH on the release of ACh in the rat hippocampus. These results indicate that Y-29794 is an orally active, potent and specific PPCE inhibitor and should be of value in studies on the physiological role of the enzyme in neuropeptide metabolism especially in memory process.

Hydrolysis of substance P in the rabbit retina: II. The role of a membrane-associated acetylcholine-sensitive metalloendopeptidase. An in vitro study

Studies in the rabbit retina have shown that infusion of exogenous acetylcholine (ACh) into the vitreal chamber leads to an increase in the amount of substance P (SP) immunoreactivity (Goebel and Pourcho, submitted). This increase was determined to be independent of new peptide synthesis, suggesting that the elevated level of SP is the result of ACh inhibition of an SP-degrading protease. This phenomenon has now been confirmed in vitro in both tissue slice and retinal homogenate assays. These studies have shown that ACh decreases the rate of SP hydrolysis in a concentration dependent manner. Recovery of SP hydrolytic activity following ACh inhibition was found to be directly proportional to the amount of acetylcholinesterase (AChE) activity in the membrane fraction. Specific protease inhibitors were used to determine the relative contributions of membrane associated retinal enzymes to SP-hydrolysis. In the presence of 1 mM 1,10-phenanthroline or p-chloromercuribenzenesulfonic acid all SP-hydrolytic activity was abolished, indicating that the enzyme(s) responsible for the degradation of the peptide is a metallopeptidase. The ACh sensitive retinal enzyme was found to be concentrated in the membrane fraction where it accounts for approximately 70% of the SP hydrolytic activity. Although the precise identity of this enzyme remains to be determined, the present evidence indicates that it shares many of the characteristics of the enzyme substance P-degrading endopeptidase (Endo et al. 1988, 1989). Enkephalinase activity was also found, contributing to 28% of the hydrolytic activity in the membrane fraction. However, the activity of this enzyme was insensitive to elevated levels of ACh. After initial cleavage of SP by the primary hydrolytic enzymes, further degradation of the fragments appears to be carried out by membrane associated serine protease(s). The activity exhibited by this class of enzymes was inhibited by DFP treatment and was not sensitive to ACh. Although AChE does not make a major contribution to the hydrolysis of SP, it does participate in peptide degradation via its esterase activity which controls the level of ACh, thereby modulating the primary SP-hydrolytic enzyme.

Differential processing of substance P and neurokinin A by plasma dipeptidyl(amino)peptidase IV, aminopeptidase M and angiotensin converting enzyme

In addition to plasma metabolism of substance P (SP) by angiotensin converting enzyme (ACE; EC 3.4.15.1) (less than 1.0 nmol/min/ml), the majority of SP hydrolysis by rat and human plasma was due to dipeptidyl(amino)peptidase IV (DAP IV; EC 3.4.14.5) (3.15-5.91 nmol/min/ml), which sequentially converted SP to SP(3-11) and SP(5-11). In turn, the SP(5-11) metabolite was rapidly hydrolyzed by rat and human plasma aminopeptidase M (AmM; EC 3.4.11.2) (24.2-25.5 nmol/min/ml). The Km values of SP for DAP IV and of SP(5-11) for AmM ranged from 32.7 to 123 microM. In contrast, neurokinin A (NKA) was resistant to both ACE and DAP IV but was subject to N-terminal hydrolysis by AmM (3.76-10.8 nmol/min/ml; Km = 90.7 microM). These data demonstrate differential processing of SP and NKA by specific peptidases in rat and human plasma.

Purification and characterization of human brain prolyl endopeptidase

Prolyl endopeptidase (EC 3.4.21.26) was purified from human brain by a series of column-chromatographic steps using DEAE-cellulose DE-52, hydroxyapatite, phenyl-Sepharose, Sephacryl S-200 and f.p.l.c. (Mono Q). The enzyme was purified by a factor of 943 and was homogeneous in a SDS/polyacrylamide gel as judged by Coomassie Blue staining. The Mr estimated by SDS/PAGE is 79,600, and under native conditions on Sephacryl S-200 it is 85,600. Therefore the enzyme exists as a monomer. With benzyloxycarbonylglycylproline p-nitroanilide as substrate, the optimum pH of the enzyme is 6.8, and with the substrate concentration between 0.059 mM and 0.37 mM the Km is 9.0 x 10(-4) M. The pI of the enzyme is 4.75. The enzyme is classified as a serine proteinase, as it is strongly inhibited by di-isopropyl fluorophosphate. However, other serine proteinase inhibitors do not inhibit the enzyme significantly, suggesting that the active site of prolyl endopeptidase differs from that of classical serine proteinases such as trypsin. Polyclonal antibodies were raised against purified human brain prolyl endopeptidase in rabbits. Western-blot analysis, enzyme-inhibition assays, antibody binding and immunoprecipitation experiments indicated that the polyclonal antibodies are both specific and inhibitory to the enzyme activity.

Phosphoramidon potentiates mammalian tachykinin-induced biting, licking and scratching behaviour in mice

The effects of peptidase inhibitors were examined upon behavioural responses including scratch, bite and lick produced by intrathecal (IT) injection of substance P (SP) and neurokinin A (NK A) in mice. Phosphoramidon (0.002-2.0 nmol), an endopeptidase-24.11 inhibitor, simultaneously injected with SP or NK A, remarkably enhanced and prolonged SP- or NK A-induced behavioural response in a dose-dependent manner. The behavioural response to SP was significantly increased by 2.0 nmol of bestatin, an aminopeptidase inhibitor, but not by 1.0 nmol. Captopril, an angiotensin-converting enzyme inhibitor, was without effect on both tachykinin-induced responses. When phosphoramidon was injected together with bestatin and captopril which have no significant effect alone, SP- or NK A-induced behavioral response was significantly increased. These data suggest that endopeptidase-24.11 may be an important enzyme responsible for terminating of SP- or NK A-induced behavioral response at the spinal cord level.