Aminopeptidase P from rat brain. Purification and action on bioactive peptides

Modulation of autoimmune diabetes by N-ethyl-N-nitrosourea- induced mutations in non-obese diabetic mice

Genetic association studies of type 1 diabetes (T1D) in humans, and in congenic non-obese diabetic (NOD) mice harboring DNA segments from T1D-resistant mice, face the challenge of assigning causation to specific gene variants among many within loci that affect disease risk. Here, we created random germline mutations in NOD/NckH mice and used automated meiotic mapping to identify mutations modifying T1D incidence and age of onset. In contrast with association studies in humans or congenic NOD mice, we analyzed a relatively small number of genetic changes in each pedigree, permitting implication of specific mutations as causative. Among 844 mice from 14 pedigrees bearing 594 coding/splicing changes, we identified seven mutations that accelerated T1D development, and five that delayed or suppressed T1D. Eleven mutations affected genes not previously known to influence T1D (Xpnpep1, Herc1, Srrm2, Rapgef1, Ppl, Zfp583, Aldh1l1, Col6a1, Ccdc13, Cd200r1, Atrnl1). A suppressor mutation in Coro1a validated the screen. Mutagenesis coupled with automated meiotic mapping can detect genes in which allelic variation influences T1D susceptibility in NOD mice. Variation of some of the orthologous/paralogous genes may influence T1D susceptibility in humans.

Molecular characterization of a novel aspartyl aminopeptidase that contributes to the increase in glutamic acid content in chicken meat during cooking

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Chicken homogenate produced significantly more free glutamic acid than beef while heating.

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DNPEP protein was detected in chicken meat extract by immunoblotting.

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Chicken DNPEP gene expression was detected in the breast and thigh muscles by RT-PCR.

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Recombinant cDNPEP showed high preference for glutamyl residues over aspartyl residues.

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The contribution of DNPEP to a great increase in glutamate in chicken meat during cooking was expected.

The enzyme involved in the increase in glutamic acid content in chicken meat during cooking was identified and characterized. Chicken homogenate produced significantly more free glutamic acid and exhibited higher glutamyl p-nitroanilide (Glu-pNA) hydrolyzing activity than beef when heat cooked. Amino acid sequencing revealed the presence of aspartyl aminopeptidase (DNPEP) in chicken meat. Using RT-PCR, DNPEP gene expression was detected in chicken breast and thigh muscles, liver, and small intestine, together with various other peptidase genes. Full-length DNPEP cDNA was cloned, and recombinant chicken DNPEP (cDNPEP) was expressed in Escherichia coli. cDNPEP showed five-fold higher activity against Glu-pNA than against aspartyl-pNA, which represents a different substrate specificity than observed for recombinant bovine DNPEP (bDNPEP). The Km values of both DNPEPs with Glu p-NA substrates indicated a higher affinity of cDNPEP for glutamyl residues. This unique substrate specificity of cDNPEP contributes to efficient glutamic acid production in chickens.

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

Investigation of the proton relay system operative in human cystosolic aminopeptidase P

Aminopeptidase P, a metalloprotease, targets Xaa-Proline peptides for cleavage [1-4]. There are two forms of human AMPP, a membrane-bound form (hmAMPP) and a soluble cytosolic form (hcAMPP)[5]. Similar to the angiotensin-I-converting enzyme, AMPP plays an important role in the catabolism of inflammatory and vasoactive peptides, known as kinins. The plasma kinin, bradykinin, was used as the substrate to conduct enzymatic activity analyses and to determine the Michaelis constant (Km) of 174 μM and the catalytic rate constant (kcat) of 10.8 s-1 for hcAMPP. Significant differences were observed in the activities of Y527F and R535A hcAMPP mutants, which displayed a 6-fold and 13.5-fold for decrease in turnover rate, respectively. Guanidine hydrochloride restored the activity of R535A hcAMPP, increasing the kcat/Km 20-fold, yet it had no impact on the activities of the wild-type or Y527F mutant hcAMPPs. Activity restoration by guanidine derivatives followed the order guanidine hydrochloride >> methyl-guanidine > amino-guanidine > N-ethyl-guanidine. Overall, the results indicate the participation of R535 in the hydrogen bond network that forms a proton relay system. The quaternary structure of hcAMPP was determined by using analytical ultracentrifugation (AUC). The results show that alanine replacement of Arg535 destabilizes the hcAMPP dimer and that guanidine hydrochloride restores the native monomer-dimer equilibrium. It is proposed that Arg535 plays an important role in hcAMMP catalysis and in stabilization of the catalytically active dimeric state.

Proteome profiling of clear cell renal cell carcinoma in von Hippel-Lindau patients highlights upregulation of Xaa-Pro aminopeptidase-1, an anti-proliferative and anti-migratory exoprotease

Patients of the von Hippel-Lindau (VHL) disease frequently develop clear cell renal cell carcinoma (ccRCC). Using archived, formalin-fixed, paraffin-embedded (FFPE) samples, we sought to determine global proteome alterations that distinguish ccRCC tissue from adjacent, non-malignant kidney tissue in VHL-patients. Our quantitative proteomic analysis clearly discriminated tumor and non-malignant tissue. Significantly dysregulated proteins were distinguished using the linear models for microarray data algorithm. In the ccRCC tissue, we noticed a predominant under-representation of proteins involved in the tricarboxylic acid cycle and an increase in proteins involved in glycolysis. This profile possibly represents a proteomic fingerprint of the "Warburg effect", which is a molecular hallmark of ccRCC. Furthermore, we observed an increase in proteins involved in extracellular matrix organization. We also noticed differential expression of many exoproteases in the ccRCC tissue. Of particular note were opposing alterations of Xaa-Pro Aminopeptidases-1 and -2 (XPNPEP-1 and -2): a strong decrease of XPNPEP-2 in ccRCC was accompanied by abundant presence of the related protease XPNPEP-1. In both cases, we corroborated the proteomic results by immunohistochemical analysis of ccRCC and adjacent, non-malignant kidney tissue of VHL patients. To functionally investigate the role of XPNPEP-1 in ccRCC, we performed small-hairpin RNA mediated XPNPEP-1 expression silencing in 786-O ccRCC cells harboring a mutated VHL gene. We found that XPNPEP-1 expression dampens cellular proliferation and migration. These results suggest that XPNPEP-1 is likely an anti-target in ccRCC. Methodologically, our work further validates the robustness of using FFPE material for quantitative proteomics.

Structure of the human aminopeptidase XPNPEP3 and comparison of its in vitro activity with Icp55 orthologs: Insights into diverse cellular processes

The human aminopeptidase XPNPEP3 is associated with cystic kidney disease and TNF-TNFR2 cellular signaling. Its yeast and plant homolog Icp55 processes several imported mitochondrial matrix proteins leading to their stabilization. However, the molecular basis for the diverse roles of these enzymes in the cell is unknown. Here, we report the crystal structure of human XPNPEP3 with bound apstatin product at 1.65 Å resolution, and we compare its in vitro substrate specificity with those of fungal Icp55 enzymes. In contrast to the suggestions by earlier in vivo studies of mitochondrial processing, we found that these enzymes are genuine Xaa-Pro aminopeptidases, which hydrolyze peptides with proline at the second position (P1'). The mitochondrial processing activity involving cleavage of peptides lacking P1' proline was also detected in the purified enzymes. A wide proline pocket as well as molecular complementarity and capping at the S1 substrate site of XPNPEP3 provide the necessary structural features for processing the mitochondrial substrates. However, this activity was found to be significantly lower as compared with Xaa-Pro aminopeptidase activity. Because of similar activity profiles of Icp55 and XPNPEP3, we propose that XPNPEP3 plays the same mitochondrial role in humans as Icp55 does in yeast. Both Xaa-Pro aminopeptidase and mitochondrial processing activities of XPNPEP3 have implications toward mitochondrial fitness and cystic kidney disease. Furthermore, the presence of both these activities in Icp55 elucidates the unexplained processing of the mitochondrial cysteine desulfurase Nfs1 in yeast. The enzymatic and structural analyses reported here provide a valuable molecular framework for understanding the diverse cellular roles of XPNPEP3.

Evidence for genetic heterogeneity between clinical subtypes of bipolar disorder

We performed a genome-wide association study of 6447 bipolar disorder (BD) cases and 12 639 controls from the International Cohort Collection for Bipolar Disorder (ICCBD). Meta-analysis was performed with prior results from the Psychiatric Genomics Consortium Bipolar Disorder Working Group for a combined sample of 13 902 cases and 19 279 controls. We identified eight genome-wide significant, associated regions, including a novel associated region on chromosome 10 (rs10884920; P=3.28 × 10-8) that includes the brain-enriched cytoskeleton protein adducin 3 (ADD3), a non-coding RNA, and a neuropeptide-specific aminopeptidase P (XPNPEP1). Our large sample size allowed us to test the heritability and genetic correlation of BD subtypes and investigate their genetic overlap with schizophrenia and major depressive disorder. We found a significant difference in heritability of the two most common forms of BD (BD I SNP-h2=0.35; BD II SNP-h2=0.25; P=0.02). The genetic correlation between BD I and BD II was 0.78, whereas the genetic correlation was 0.97 when BD cohorts containing both types were compared. In addition, we demonstrated a significantly greater load of polygenic risk alleles for schizophrenia and BD in patients with BD I compared with patients with BD II, and a greater load of schizophrenia risk alleles in patients with the bipolar type of schizoaffective disorder compared with patients with either BD I or BD II. These results point to a partial difference in the genetic architecture of BD subtypes as currently defined.

Crystal structure of X-prolyl aminopeptidase from Caenorhabditis elegans: A cytosolic enzyme with a di-nuclear active site

Eukaryotic aminopeptidase P1 (APP1), also known as X‐prolyl aminopeptidase (XPNPEP1) in human tissues, is a cytosolic exopeptidase that preferentially removes amino acids from the N‐terminus of peptides possessing a penultimate N‐terminal proline residue. The enzyme has an important role in the catabolism of proline containing peptides since peptide bonds adjacent to the imino acid proline are resistant to cleavage by most peptidases. We show that recombinant and catalytically activeCaenorhabditis elegans APP‐1 is a dimer that uses dinuclear zinc at the active site and, for the first time, we provide structural information for a eukaryotic APP‐1 in complex with the inhibitor, apstatin. Our analysis reveals thatC. elegans APP‐1 shares similar mode of substrate binding and a common catalytic mechanism with other known X‐prolyl aminopeptidases.

We present the crystal structure ofC. elegans APP‐1 both in bound and unbound forms.

We showC. elegans APP‐1 uses dinuclear zinc at the active site.

We confirm thatC. elegans APP‐1 is biological dimer.

Our analysis reveals thatC. elegans APP‐1 shares a common catalytic mechanism with other X‐prolyl aminopeptidases.

The association of serum prolidase activity with developmental dysplasia of the hip

The purpose of this study was to evaluate serum prolidase activity in patients with developmental dysplasia of the hip (DDH). Prolidase enzyme activity was measured spectrophotometrically to pointing out the collagen metabolism. The prolidase activity in patients with DDH was significantly higher than that in the control group (p = 0.002). Furthermore, there was positive correlation between prolidase activity and dysplasia level. Increased serum prolidase activity may have played a role in the presence of DDH. We therefore hypothesized that the increased prolidase activity related to collagen turnover may be associated with etiopathogenesis and/or the progression of the disease.

Developmental retardation, microcephaly, and peptiduria in mice without aminopeptidase P1

Cytosolic aminopeptidase P1 (APP1) is one of the three known mammalian aminopeptidase Ps (APPs) that cleave the N-terminal amino acid residue of peptides in which the penultimate amino acid is proline. In mammals, many biologically active peptides have a highly conserved N-terminal penultimate proline. However, little is known about the physiological role of APP1. In addition, there is no direct evidence to associate a deficiency in APP1 with metabolic diseases. Although two human subjects with reduced APP activity exhibited peptiduria, it is unclear which of the three APP isoforms is responsible for this disorder. In this study, we generated APP1-deficient mice by knocking out Xpnpep1. Mouse APP1 deficiency causes severe growth retardation, microcephaly, and modest lethality. In addition, imino-oligopeptide excretion was observed in urine samples from APP1-deficient mice. These results suggest an essential role for APP1-mediated peptide metabolism in body and brain development, and indicate a strong causal link between APP1 deficiency and peptiduria.

Production, active staining and gas chromatography assay analysis of recombinant aminopeptidase P from Lactococcus lactis ssp. lactis DSM 20481

The aminopeptidase P (PepP, EC 3.4.11.9) gene from Lactococcus lactis ssp. lactis DSM 20481 was cloned, sequenced and expressed recombinantly in E. coli BL21 (DE3) for the first time. PepP is involved in the hydrolysis of proline-rich proteins and, thus, is important for the debittering of protein hydrolysates. For accurate determination of PepP activity, a novel gas chromatographic assay was established. The release of L-leucine during the hydrolysis of L-leucine-L-proline-L-proline (LPP) was examined for determination of PepP activity. Sufficient recombinant PepP production was achieved via bioreactor cultivation at 16 °C, resulting in PepP activity of 90 μkatLPP Lculture-1. After automated chromatographic purification by His-tag affinity chromatography followed by desalting, PepP activity of 73.8 μkatLPP Lculture-1 was achieved. This was approximately 700-fold higher compared to the purified native PepP produced by Lactococcus lactis ssp. lactis NCDO 763 as described in literature. The molecular weight of PepP was estimated to be ~ 40 kDa via native-PAGE together with a newly developed activity staining method and by SDS-PAGE. Furthermore, the kinetic parameters Km and Vmax were determined for PepP using three different tripeptide substrates. The purified enzyme showed a pH optimum between 7.0 and 7.5, was most active between 50°C and 60°C and exhibited reasonable stability at 0°C, 20°C and 37°C over 15 days. PepP activity could be increased 6-fold using 8.92 mM MnCl2 and was inhibited by 1,10-phenanthroline and EDTA.

The Analgesic Activity of Bestatin as a Potent APN Inhibitor

Bestatin, a small molecular weight dipeptide, is a potent inhibitor of various aminopeptidases as well as LTA4 hydrolase. Various physiological functions of Bestatin have been identified, viz.: (1) an immunomodifier for enhancing the proliferation of normal human bone marrow granulocyte-macrophage progenitor cells to form CFU-GM colonies; Bestatin exerts a direct stimulating effect on lymphocytes via its fixation on the cell surface and an indirect effect on monocytes via aminopeptidase B inhibition of tuftsin catabolism; (2) an immunorestorator and curative or preventive agent for spontaneous tumor; Bestatin alone or its combination with chemicals can prolongate the disease-free interval and survival period in adult acute or chronic leukemia, therefore, it was primarily marketed in 1987 in Japan as an anticancer drug and servers as the only marketed inhibitor of Aminopeptidase N (APN/CD13) to cure leukemia to date; (3) a pan-hematopoietic stimulator and restorator; Bestatin promotes granulocytopoiesis and thrombocytopoiesis in vitro and restores them in myelo-hypoplastic men; (4) an inhibitor of several natural opioid peptides. Based on the knowledge that APN can cleave several bioactive neuropeptides such as Met-enkaphalins, Leu-enkaphalins, beta-Endorphin, and so on, the anti-aminopeptidase action of Bestatin also allows it to protect endopeptides against their catabolism, exhibiting analgesic activity. Although many scientific studies and great accomplishments have been achieved in this field, a large amount of problems are unsolved. This article reviews the promising results obtained for future development of the analgesic activity of Bestatin that can be of vital interest in a number of severe and chronic pain syndromes.

Evidence for catalytic roles for Plasmodium falciparum aminopeptidase P in the food vacuole and cytosol

The metalloenzyme aminopeptidase P catalyzes the hydrolysis of amino acids from the amino termini of peptides with a prolyl residue in the second position. The human malaria parasite Plasmodium falciparum expresses a homolog of aminopeptidase P during its asexual intraerythrocytic cycle. P. falciparum aminopeptidase P (PfAPP) shares with mammalian cytosolic aminopeptidase P a three-domain, homodimeric organization and is most active with Mn(II) as the cofactor. A distinguishing feature of PfAPP is a 120-amino acid amino-terminal extension that appears to be removed from the mature protein. PfAPP is present in the food vacuole and cytosol of the parasite, a distribution that suggests roles in vacuolar hemoglobin catabolism and cytosolic peptide turnover. To evaluate the plausibility of these putative functions, the stability and kinetic properties of recombinant PfAPP were evaluated at the acidic pH of the food vacuole and at the near-neutral pH of the cytosol. PfAPP exhibited high stability at 37 degrees C in the pH range 5.0-7.5. In contrast, recombinant human cytosolic APP1 was unstable and formed a high molecular weight aggregate at acidic pH. At both acidic and slightly basic pH values, PfAPP efficiently hydrolyzed the amino-terminal X-Pro bond of the nonapeptide bradykinin and of two globin pentapeptides that are potential in vivo substrates. These results provide support for roles for PfAPP in peptide catabolism in both the food vacuole and the cytosol and suggest that PfAPP has evolved a dual distribution in response to the metabolic needs of the intraerythrocytic parasite.

Enzymatic degradation of endomorphins

Centrally acting plant opiates, such as morphine, are the most frequently used analgesics for the relief of severe pain, even though their undesired side effects are serious limitation to their usefulness. The search for new therapeutics that could replace morphine has been mainly focused on the development of peptide analogs or peptidomimetics with high selectivity for one receptor type and high bioavailability, that is good blood-brain barrier permeability and enzymatic stability. Drugs, in order to be effective, must be able to reach the target tissue and to remain metabolically stable to produce the desired effects. The study of naturally occurring peptides provides a rational and powerful approach in the design of peptide therapeutics. Endogenous opioid peptides, endomorphin-1 and endomorphin-2, are two potent and highly selective mu-opioid receptor agonists, discovered only a decade ago, which display potent analgesic activity. However, extensive studies on the possible use of endomorphins as analgesics instead of morphine met with failure due to their instability. This review deals with the recent investigations that allowed determine degradation pathways of endomorphins in vitro and in vivo and propose modifications that will lead to more stable analogs.

Structure of human cytosolic X-prolyl aminopeptidase: a double Mn(II)-dependent dimeric enzyme with a novel three-domain subunit

X-prolyl aminopeptidases catalyze the removal of a penultimate prolyl residue from the N termini of peptides. Mammalian X-prolyl aminopeptidases are shown to be responsible for the degradation of bradykinin, a blood pressure regulator peptide, and have been linked to myocardial infarction. The x-ray crystal structure of human cytosolic X-prolyl aminopeptidase (XPN-PEP1) was solved at a resolution of 1.6 angstroms. The structure reveals a dimer with a unique three-domain organization in each subunit, rather than the two domains common to all other known structures of X-prolyl aminopeptidase and prolidases. The C-terminal catalytic domain of XPNPEP1 coordinates two metal ions and shares a similar fold with other prolyl aminopeptidases. Metal content analysis and activity assays confirm that the enzyme is double Mn(II) dependent for its activity, which contrasts with the previous notion that each XPNPEP1 subunit contains only one Mn(II) ion. Activity assays on an E41A mutant demonstrate that the acidic residue, which was considered as a stabilizing factor in the protonation of catalytic residue His498, plays only a marginal role in catalysis. Further mutagenesis reveals the significance of the N-terminal domain and dimerization for the activity of XPNPEP1, and we provide putative structural explanations for their functional roles. Structural comparisons further suggest mechanisms for substrate selectivity in different X-prolyl peptidases.

The significance of brain aminopeptidases in the regulation of the actions of angiotensin peptides in the brain

From the outset, the concept of a brain renin-angiotensin system (RAS) has been controversial and this controversy continues to this day. In addition to the unresolved questions as to the means by which, and location(s) where brain Ang II is synthesized, and the uncertainties regarding the functionality of the different subtypes of Ang II receptors in the brain, a new controversy has arisen with respect to the identity of the angiotensin peptide(s) that activate brain AT(1) receptors. While it has been known for some time that Ang III can activate Ang II receptors with equivalent or near-equivalent efficacy to Ang II, it has been proposed that in the brain, only Ang III is active. This proposal, which we have named "The Angiotensin III Hypothesis" states that Ang II must be converted to Ang III in order to activate brain AT(1) receptors. This review examines several aspects of the controversies regarding the brain RAS with a special focus on brain aminopeptidases, studies that either support or refute The Angiotensin III Hypothesis, and the implications of The Angiotensin III Hypothesis for the activity of the brain RAS. It also addresses the need for further research that can test The Angiotensin III Hypothesis and definitively identify the angiotensin peptide(s) that activate brain AT(1) receptor-mediated effects.

Cord blood prolidase activity correlates with gestational age and birth weight

BACKGROUND

Prolidase, a specific iminopeptidase involved in collagen turnover, is especially active in growing tissues.

OBJECTIVES

To investigate the relationship between cord blood prolidase activity and both birth weight and gestational age.

METHODS

Cord blood was collected consecutively from 50 healthy newborns (35 term, 15 preterm). Prolidase activity was measured in the samples using standard methods.

RESULTS

Themean +/- SD cord blood prolidase activity was 41.4 +/- 6.9 U/l in term infants and 35.2 +/- 8.0 U/l in preterm infants and these were significantly different (p < 0.01). There were positive correlations between cord blood prolidase and both birth weight (r = 0.533, p < 0.01) and gestational age (r = 0.806, p < 0.01).

CONCLUSION

Cord blood prolidase activity may be a good indicator of fetal maturation and gestational age.

Complexes of mutants of Escherichia coli aminopeptidase P and the tripeptide substrate ValProLeu

Aminopeptidase P (APPro) is a manganese-containing enzyme that catalyses the hydrolysis of the N-terminal residue of a polypeptide if the second residue is proline. Structures of APPro mutants with reduced or negligible activity have been determined in complex with the tripeptide substrate ValProLeu. In the complex of Glu383Ala APPro with ValProLeu one of the two metal sites is only partly occupied, indicating an essential role for Glu383 in metal binding in the presence of substrate. His361Ala APPro clearly possesses residual activity as the ValProLeu substrate has been cleaved in the crystals; difference electron density consistent with bound ProLeu dipeptide and a disordered Val amino acid is present at the active site. Contrary to previous suggestions, the His243Ala mutant is capable of binding substrate. The structure of the His243Ala APPro complex with ValProLeu shows that the peptide interacts with one of the active-site metal atoms via its terminal amino group. The implications of these complexes for the roles of the respective residues in APPro catalysis are discussed.

The endomorphin system and its evolving neurophysiological role

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) are two endogenous opioid peptides with high affinity and remarkable selectivity for the mu-opioid receptor. The neuroanatomical distribution of endomorphins reflects their potential endogenous role in many major physiological processes, which include perception of pain, responses related to stress, and complex functions such as reward, arousal, and vigilance, as well as autonomic, cognitive, neuroendocrine, and limbic homeostasis. In this review we discuss the biological effects of endomorphin-1 and endomorphin-2 in relation to their distribution in the central and peripheral nervous systems. We describe the relationship between these two mu-opioid receptor-selective peptides and endogenous neurohormones and neurotransmitters. We also evaluate the role of endomorphins from the physiological point of view and report selectively on the most important findings in their pharmacology.

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.

Increased oxidative stress and its relation with collagen metabolism in knee osteoarthritis

The purpose of this study was to determine serum oxidative/antioxidative status in patients with knee osteoarthritis and its relation with prolidase activity, which plays an important role in collagen metabolism. Serum antioxidative status was evaluated by measuring total antioxidant capacity (TAC), thiol level and catalase enzyme activity in patients with osteoarthritis and in healthy controls. Serum oxidative status was evaluated by measuring total peroxide (TP) and lipid hydroperoxide. Oxidative stress index (OSI) was calculated. Prolidase enzyme activity was measured to investigate the collagen metabolism. Serum TAC, thiol level, catalase activity and prolidase activity were significantly lower in patients than in controls (P < 0.001, for all). In contrast, TP, lipid hydroperoxide and OSI values were significantly higher in patients than in controls (P < 0.001 for all). Further, prolidase activity was negatively correlated with TP and OSI, and positively correlated with TAC. The present results indicate that the oxidant parameters increased and antioxidant parameters decreased in patients with osteoarthritis; therefore, these patients may be exposed to a potent oxidative stress. Decreased collagen metabolism may be related with oxidative stress, which has a role in the ethiopathogenesis and/or in the progression of the disease.

A novel peptide from the ACEI/BPP-CNP precursor in the venom of Crotalus durissus collilineatus

In crotaline venoms, angiotensin-converting enzyme inhibitors [ACEIs, also known as bradykinin potentiating peptides (BPPs)], are products of a gene coding for an ACEI/BPP-C-type natriuretic peptide (CNP) precursor. In the genes from Bothrops jararaca and Gloydius blomhoffii, ACEI/BPP sequences are repeated. Sequencing of a cDNA clone from venom glands of Crotalus durissus collilineatus showed that two ACEIs/BPPs are located together at the N-terminus, but without repeats. An additional sequence for CNP was unexpectedly found at the C-terminus. Homologous genes for the ACEI/BPP-CNP precursor suggest that most crotaline venoms contain both ACEIs/BPPs and CNP. The sequence of ACEIs/BPPs is separated from the CNP sequence by a long spacer sequence. Previously, there was no evidence that this spacer actually coded any expressed peptides. Aird and Kaiser (1986, unpublished) previously isolated and sequenced a peptide of 11 residues (TPPAGPDVGPR) from Crotalus viridis viridis venom. In the present study, analysis of the cDNA clone from C. d. collilineatus revealed a nearly identical sequence in the ACEI/BPP-CNP spacer. Fractionation of the crude venom by reverse phase HPLC (C(18)), and analysis of the fractions by mass spectrometry (MS) indicated a component of 1020.5 Da. Amino acid sequencing by MS/MS confirmed that C. d. collilineatus venom contains the peptide TPPAGPDGGPR. Its high proline content and paired proline residues are typical of venom hypotensive peptides, although it lacks the usual N-terminal pyroglutamate. It has no demonstrable hypotensive activity when injected intravenously in rats; however, its occurrence in the venoms of dissimilar species suggests that its presence is not accidental. Evidence suggests that these novel toxins probably activate anaphylatoxin C3a receptors.

Cloning, expression, and characterization of aminopeptidase P from the hyperthermophilic archaeon Thermococcus sp. strain NA1

Genomic analysis of a hyperthermophilic archaeon, Thermococcus sp. strain NA1, revealed the presence of a 1,068-bp open reading frame encoding a protein consisting of 356 amino acids with a calculated molecular mass of 39,714 Da (GenBank accession no. DQ144132). Sequence analysis showed that it was similar to the putative aminopeptidase P (APP) of Thermococcus kodakaraensis KOD1. Amino acid residues important for catalytic activity and the metal binding ligands conserved in bacterial, nematode, insect, and mammalian APPs were also conserved in the Thermococcus sp. strain NA1 APP. The archaeal APP, designated TNA1_APP (Thermococcus sp. strain NA1 APP), was cloned and expressed in Escherichia coli. The recombinant enzyme hydrolyzed the amino-terminal Xaa-Pro bond of Lys(Nepsilon-Abz)-Pro-Pro-pNA and the dipeptide Met-Pro (Km, 0.96 mM), revealing its functional identity. Further enzyme characterization showed the enzyme to be a Co2+-, Mn2+-, or Zn2+-dependent metallopeptidase. Optimal APP activity with Met-Pro as the substrate occurred at pH 5 and a temperature of 100 degrees C. The APP was thermostable, with a half-life of >100 min at 80 degrees C. This study represents the first characterization of a hyperthermophilic archaeon APP.

The kallikrein-kinin system: current and future pharmacological targets

The kallikrein-kinin system is an endogenous metabolic cascade, triggering of which results in the release of vasoactive kinins (bradykinin-related peptides). This complex system includes the precursors of kinins known as kininogens and mainly tissue and plasma kallikreins. The pharmacologically active kinins, which are often considered as either proinflammatory or cardioprotective, are implicated in many physiological and pathological processes. The interest of the various components of this multi-protein system is explained in part by the multiplicity of its pharmacological activities, mediated not only by kinins and their receptors, but also by their precursors and their activators and the metallopeptidases and the antiproteases that limit their activities. The regulation of this system by serpins and the wide distribution of the different constituents add to the complexity of this system, as well as its multiple relationships with other important metabolic pathways such as the renin-angiotensin, coagulation, or complement pathways. The purpose of this review is to summarize the main properties of this kallikrein-kinin system and to address the multiple pharmacological interventions that modulate the functions of this system, restraining its proinflammatory effects or potentiating its cardiovascular properties.

Kinetic and crystallographic analysis of mutant Escherichia coli aminopeptidase P: insights into substrate recognition and the mechanism of catalysis

Aminopeptidase P (APPro) is a manganese-dependent enzyme that cleaves the N-terminal amino acid from polypeptides where the second residue is proline. APPro shares a similar fold, substrate specificity, and catalytic mechanism with methionine aminopeptidase and prolidase. To investigate the roles of conserved residues at the active site, seven mutant forms of APPro were characterized kinetically and structurally. Mutation of individual metal ligands selectively abolished binding of either or both Mn(II) atoms at the active site, and none of these metal-ligand mutants had detectable catalytic activity. Mutation of the conserved active site residues His243 and His361 revealed that both are required for catalysis. We propose that His243 stabilizes substrate binding through an interaction with the carbonyl oxygen of the requisite proline residue of a substrate and that His361 stabilizes substrate binding and the gem-diol catalytic intermediate. Sequence, structural, and kinetic analyses reveal that His350, conserved in APPro and prolidase but not in methionine aminopeptidase, forms part of a hydrophobic binding pocket that gives APPro its proline specificity. Further, peptides in which the required proline residue is replaced by N-methylalanine or alanine are cleaved by APPro, but they are extremely poor substrates due to a loss of interactions between the prolidyl ring of the substrate and the hydrophobic proline-binding pocket.

Distribution of aminopeptidase P like immunoreactivity in the olfactory system and brain of frog, Microhyla ornate

The enzyme aminopeptidase P (AP-P) is encountered in diverse vertebrate and invertebrate phyla and is known to act on proteins and peptides by releasing their N-terminal amino acid when the penultimate amino acid is proline. The present study is the first attempt at visualizing distribution of this polypeptide in the brain of a vertebrate species. The distribution of this enzyme was studied immunocytochemically in the forebrain of frog Microhyla ornata using antisera directed against cytosolic aminopeptidase P (DAP-P) of Drosophila melanogaster. Receptor cells in the olfactory epithelium exhibited strong AP-P like immunoreaction (ir). Immunoreactive fibers arising from the olfactory epithelium as well as vomeronasal organ joined the olfactory nerve, entered into the olfactory bulb, or accessory olfactory bulb and terminated in distinct glomerular formations. Some immunoreactive fibers traveled caudally and terminated in discrete areas in the telencephalon or diencephalon. Strong AP-P-ir was also seen in the cells of pars intermedia and pars distalis of the pituitary. The pattern of immunoreactivity suggests a role for AP-P in the processing of olfactory information and in hypophysial regulation.

Novel 3-amino-2-hydroxy acids containing protease inhibitors. Part 1: Synthesis and kinetic characterization as aminopeptidase P inhibitors

Novel, potent inhibitors of aminopeptidase P, containing a 3-amino-2-hydroxy acid and a proline or a proline analogues, have been prepared. One part of the bestatin-derived inhibitors was found to inhibit APP from Escherichia coli and from rat intestine according to a mixed-type mechanism, with Ki values up to 1.26 microM. The other compounds, 3-amino-2-hydroxy acyl prolines of a different configuration, inhibit APP competitively, according to a slow-binding mechanism, with Ki values in the nanomolar up to the micromolar range.

Aminopeptidase P isozyme expression in human tissues and peripheral blood mononuclear cell fractions

Aminopeptidase P (APP) isoforms specifically remove the N-terminal amino acid from peptides that have a proline residue in the second position. The mRNA levels of three different isoforms, each coded by a different gene, were determined in 16 human tissues and in peripheral blood mononuclear cell (PBMC) fractions by RT-PCR. The cytosolic isoform, APP1, and the cell surface membrane-bound isoform, APP2, are expressed in all of the human tissues and PBMC fractions examined. The very high expression of APP2 mRNA in kidney compared to other tissues was confirmed by enzyme activity measurements. Among the PBMC fractions, APP2 expression is highest in resting CD8(+) T cells, but decreases in these cells following their activation with phytohemagglutinin; in contrast, expression of APP2 increases in CD4(+) T cells upon activation. The third isoform, APP3, is a hypothetical protein identified by nucleotide sequencing. A detailed analysis of its amino acid sequence confirmed that the protein is an aminopeptidase P-like enzyme with greater similarity to Escherichia coli APP than to either APP1 or APP2. Two splice variants of APP3 exist, one of which is predicted to have a mitochondrial localization (APP3m) while the other is cytosolic (APP3c). Both forms are variably expressed in all of the human tissues and PBMC fractions examined.

Human recombinant membrane-bound aminopeptidase P: production of a soluble form and characterization using novel, internally quenched fluorescent substrates

APP (aminopeptidase P) has the unique ability to cleave the N-terminal amino acid residue from peptides exhibiting a proline at P(1)'. Despite its putative involvement in the processing of bioactive peptides, among them the kinins, little is known about the physiological roles of both human forms of APP. The purpose of the present study is first to engineer and characterize a secreted form of hmAPP (human membrane-bound APP). Our biochemical analysis has shown that the expressed glycosylated protein is fully functional, and exhibits enzymic parameters similar to those described previously for mAPP purified from porcine or bovine lungs or expressed from a porcine clone. This soluble form of hmAPP cross-reacts with a polyclonal antiserum raised against a 469-amino-acid hmAPP fragment produced in Escherichia coli. Secondly, we synthesized three internally quenched fluorescent peptide substrates that exhibit a similar affinity for the enzyme than its natural substrates, the kinins, and a higher affinity compared with the tripeptide Arg-Pro-Pro used until now for the quantification of APP in biological samples. These new substrates represent a helpful analytical tool for rapid and reliable screening of patients susceptible to adverse reactions associated with angiotensin-converting enzyme inhibitors or novel vasopeptidase (mixed angiotensin-converting enzyme/neprilysin) inhibitors.

Cell-surface peptidases

The cell surface has various functions: communicating with other cells, integrating into the tissue, and interacting with the extracellular matrix. Proteases play a key role in these processes. This review focuses on cell-surface peptidases (ectopeptidases, oligopeptidases) that are involved in the inactivation or activation of extracellular regulatory peptides, hormones, paracrine peptides, cytokines, and neuropeptides. The nomenclature of cell-surface peptidases is explained in relation to other proteases, and information is provided on membrane anchoring, catalytic sites, regulation, and, in particular, on their physiological and pharmacological importance. Furthermore, nonenzymatic (binding) functions and participation in intracellular signal transduction of cell surfaces peptidases are described. An overview on the different cell-surface peptidases is given, and their divergent functions are explained in detail. An example of actual pharmacological importance, dipeptidyl-peptidase IV (CD26), is discussed.

Effect of peptidases on the ability of exogenous and endogenous neurokinins to produce neurokinin 1 receptor internalization in the rat spinal cord

The ability of peptidases to restrict neurokinin 1 receptor (NK1R) activation by exogenously applied or endogenously released neurokinins was investigated by measuring NK1R internalization in rat spinal cord slices. Concentration-response curves for substance P and neurokinin A were obtained in the presence and absence of 10 microm thiorphan, an inhibitor of neutral endopeptidase (EC 3.4.24.11), plus 10 microm captopril, an inhibitor of dipeptidyl carboxypeptidase (EC 3.4.15.1). These inhibitors significantly decreased the EC50 of substance P to produce NK1R internalization from 32 to 9 nm, and the EC50 of neurokinin A from 170 to 60 nm. Substance P was significantly more potent than neurokinin A, both with and without these peptidase inhibitors. In the presence of peptidase inhibitors, neurokinin B was 10 times less potent than neurokinin A and 64 times less potent than substance P (EC50=573 nm). Several aminopeptidase inhibitors (actinonin, amastatin, bacitracin, bestatin and puromycin) failed to further increase the effect of thiorphan plus captopril on the NK1R internalization produced by 10 nm substance P. Electrical stimulation of the dorsal root produced NK1R internalization by releasing endogenous neurokinins. Thiorphan plus captopril increased NK1R internalization produced by 1 Hz stimulation, but not by 30 Hz stimulation. Therefore, NEN and DCP restrict NK1R activation by endogenous neurokinins when they are gradually released by low-frequency firing of primary afferents, but become saturated or inhibited when primary afferents fire at a high frequency.

A continuous fluorimetric assay for aminopeptidase P detailed analysis of product inhibition

Aminopeptidase P (APP; EC 3.4.11.9) is a proline-specific peptidase hydrolyzing N-terminal Xaa-Pro peptide bonds. On the basis of its unique substrate specificity it is difficult to determine enzyme activity and to estimate potential enzyme inhibitors. In this report, we describe the synthesis of a new fluorogenic substrate to assay APP. The substrate was characterized using Escherichia coli APP and rat intestine APP. The compound contains the fluorogenic 2-aminobenzoyl residue and 4-nitroanilide as internal quencher. Both enzymes hydrolyze the substrate Lys(N(epsilon)-2-aminobenzoyl)-Pro-Pro-4-nitroanilide at the Lys-Pro peptide bond with Km values in the micromolar range. Lys(N(epsilon)-2-aminobenzoyl)-Pro-Pro-4-nitroanilide is the best substrate of APP from rat intestine that is known with a Km value of 3.54 microM and a second-order rate constant of 1,142,000 M(-1) s(-1). Unfortunately, product inhibition occurs. Inhibition studies using the hydrolysis product Pro-Pro-4-nitroanilide demonstrate a linear mixed-type mechanism with a K(i) value of 20.8 microM and an alpha value of 5.1 for rat APP and a K(i) value of 76.1 microM and an alpha value of 0.4 for E. coli APP, respectively. Furthermore, the hydrolysis of the fluorogenic APP substrate catalyzed by prolyl oligopeptidase was investigated.

Identification of cytosolic leucyl aminopeptidase (EC 3.4.11.1) as the major cysteinylglycine-hydrolysing activity in rat liver

Cysteinylglycine hydrolysis is a step in the metabolism of glutathione and glutathione S-conjugates. We had previously observed that in rat liver the enzymatic activity is predominantly located in the cytosol. Here we demonstrate that cytosolic leucyl aminopeptidase (EC 3.4.11.1) is the major cysteinylglycine hydrolysing activity in rat liver. Evidence was obtained from the use of peptidase inhibitors and from immunoprecipitation studies using Pansorbin-coupled antibodies raised against hog kidney cytosolic leucyl aminopeptidase. Both isolated cytosolic leucyl aminopeptidase and the cysteinylglycine-hydrolysing activity in rat liver cytosol are bound with equal efficiency to the affinity matrix. We demonstrate that cytosolic leucyl aminopeptidase exhibits leucinamidase and cysteinylglycinase activity. Cysteinylglycine, cystinyl-bis-glycine, S-nitrosocysteinylglycine, and bimane-S-cysteinylglycine are hydrolysed at high rates; low activity is seen with leukotriene D4. Our findings establish a previously unrecognised physiological function of cytosolic leucyl aminopeptidase, participating in glutathione metabolism and in the degradation of glutathione S-conjugates via the mercapturic acid pathway.

Serum prolidase activity as a marker of osteoporosis in type 2 diabetes mellitus

OBJECTIVES

Prolidase is a specific imidodipeptidase involved in collagen degradation. The increase in the enzyme activity is believed to be correlated with the increased intensity of collagen degradation This study aimed to evaluate serum prolidase activity and urinary deoxypyridinoline cross links in type 2 diabetic subjects with and without osteoporosis assessed by bone mineral density.

DESIGN AND METHODS

Seventy-five patients (54 F/21 M) with type 2 DM and 43 age and gender matched healthy subjects (30 F/13 M) were recruited for this study. Serum prolidase activity was assessed with colorimetric determination. Urinary deoxypyridinoline (Dpy) was determined with electrochemiluminesence immunoassay.

RESULTS

Serum prolidase activity was significantly lower in patients with type 2 DM than in the healthy controls (mean +/- SEM; 43.3 +/- 1.4 U/L and 53.3 +/- 2.2 U/L respectively, p: 0.000). Non osteoporotic diabetic patients had lower serum prolidase activity (median: 25th-75th percentiles; 39.5: 30.3-50.5 U/L) than osteoporotic diabetic patients (50.0: 41.8-56.3 U/L, p: 0.030) and healthy controls (52.0: 43.0-58.0 U/L, p: 0.004). Urinary Dpy excretion was not different between osteoporotic and nonosteoporotic diabetic patients. However it was lower in both diabetic groups than the healthy controls. We did not observe a statistically significant difference between the serum prolidase activity of dislipidemic/normolipidemic, hypertensive/normotensive, obese/nonobese, insulin/OAD treated, poorly/well-controlled patients and patients with/without diabetic nephropathy and retinopathy (p > 0.05).

CONCLUSION

This study shows a significant decrease in serum prolidase activity in patients affected with type 2 DM, which may be interpreted as evidence of decreased bone resorption. Our data also suggest that serum prolidase activity may be a better marker of osteoporosis in diabetic state than Dpy.

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.

Functional expression and characterization of the cytoplasmic aminopeptidase P of Caenorhabditis elegans

Aminopeptidase P (AP-P; X-Pro aminopeptidase; EC 3.4.11.9) cleaves the N-terminal X-Pro bond of peptides and occurs in mammals as both cytosolic and plasma membrane forms, encoded by separate genes. In mammals, the plasma membrane AP-P can function as a kininase, but little is known about the physiological role of the cytosolic enzyme. The C. elegans genome contains a single gene encoding AP-P (W03G9.4), analysis of which predicts regions displaying high levels of amino-acid sequence homology between the predicted gene product and mammalian cytoplasmic AP-P, with the absolute conservation of key catalytic residues. The sequence of an EST (yk91g4), comprising the open reading frame of W03G9.4, confirmed the predicted genomic structure of the gene and the prediction that W03G9.4 codes for a nonsecreted protein with a molecular mass of 68 kDa. Nematodes transformed with a promoter reporter construct, W03G9.4:GFP, showed high levels of fluorescence in the intestine of larvae and adult hermaphrodites, indicating that the intestine is a major site of W03G9.4 expression. yk91g4 tagged with a hexahistidine and DLYDDDDK peptide epitope was expressed in Escherichia coli to yield, after affinity purification, a recombinant protein with a molecular mass of 71 kDa. The recombinant W03G9.4 removed the N-terminal amino acid from bradykinin (RPPGFSPFR), a Caenorhabditis elegans neuropeptide (KPSFVRFamide) and Lem Trp 1 (APSGFLGVRamide), but did not display activity towards angiotensin I (NRVYIHPFHL), des-Arg bradykinin and AF1 (KNEFIRFamide). The activity towards bradykinin was inhibited by EDTA and 1, 10 phenanthroline, as expected for a metalloenzyme, and also by apstatin (IC50, 1 microM), a selective inhibitor of mammalian AP-P. A Km of 45 microM and an optimum pH of 7-8 was observed with bradykinin as the substrate. The activity of the nematode AP-P, like its mammalian counterparts, was strongly influenced by metal ions, with Co2+, Mn2+ and Zn2+ all inhibiting the hydrolysis of bradykinin. We conclude that W03G9.4 codes for a cytoplasmic AP-P with very similar enzymatic properties to those of mammalian AP-P, and we suggest that the enzyme has a physiological role in the intracellular hydrolysis of proline-containing peptides absorbed from the lumen of the intestine.

Cloning, expression, and characterization of tomato (Lycopersicon esculentum) aminopeptidase P

A cDNA (LeAPP2) was cloned from tomato coding for a 654 amino acid protein of 72.7 kDa. The deduced amino acid sequence was >40% identical with that of mammalian aminopeptidase P, a metalloexopeptidase. All amino acids reported to be important for binding of the active site metals and catalytic activity, respectively, were conserved between LeAPP2 and its mammalian homologues. LeAPP2 was expressed in Escherichia coli in N-terminal fusion with glutathione S-transferase and was purified from bacterial extracts. LeAPP2 was verified as an aminopeptidase P, hydrolyzing the amino-terminal Xaa-Pro bonds of bradykinin and substance P. LeAPP2 also exhibited endoproteolytic activity cleaving, albeit at a reduced rate, the internal -Phe-Gly bond of substance P. Apparent K(m) (15.2 +/- 2.4 microm) and K(m)/k(cat) (0.94 +/- 0.11 mm(-1) x s(-1)) values were obtained for H-Lys(Abz)-Pro-Pro-pNA as the substrate. LeAPP2 activity was maximally stimulated by addition of 4 mm MnCl(2) and to some extent also by Mg(2+), Ca(2+), and Co(2+), whereas other divalent metal ions (Cu(2+), Zn(2+)) were inhibitory. Chelating agents and thiol-modifying reagents inhibited the enzyme. The data are consistent with LeAPP2 being a Mn(II)-dependent metalloprotease. This is the first characterization of a plant aminopeptidase P.

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.

Influence of degradation on binding properties and biological activity of endomorphin 1

The recently-isolated endogenous peptide endomorphin 1 has high affinity for the mu opioid receptor and plays an important role in analgesia. Several of its degradation products have been isolated from the central nervous system. Degradation products present structural similarities and may influence the receptor binding properties and biological activity of the parent compound. Therefore, we investigated how degradation of endomorphin 1 might influence ligand binding to the mu opioid receptor, the consequent activation of G proteins and its antinociceptive effect. Both N- and C-terminal truncation of endomorphin 1 resulted in peptides presenting considerably lower opioid receptor binding potency. None of these peptides had an effect on GTP binding, nor was able to produce analgesia, suggesting that degradation destroys the biological activity of endomorphin 1.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Thioxo amino acid pyrrolidides and thiazolidides: new inhibitors of proline specific peptidases

Aminopeptidase P (APP), dipeptidyl peptidase II (DP II), dipeptidyl peptidase IV (DP IV) and prolyl oligopeptidase (POP) are proline specific peptidases. Hence, they are able to cleave peptide bonds containing the imino acid proline. Amino acid pyrrolidides (Pyrr) and thiazolidides (Thia) are well-known product analogue inhibitors of DP IV and POP. For the first time we describe the influence of a thioxo amide bond, incorporated into these compounds, on the inhibition of the proline specific peptidases. Taking into account the substrate specificity of these peptidases, we have synthesized Xaa-psi[CS-N]-Pyrr and Xaa-psi[CS-N]-Thia of the amino acids Ala, Phe, Val and Ile. The inhibition constants were determined for the above mentioned proline specific peptidases isolated from different sources. As a result, the serine proteases DP II, DP IV and POP were inhibited competitively, whereas metal-dependent APP displayed a linear mixed-type inhibition with inhibition constants up to 10(-4) M. Thioxylation of Xaa-Pyrr and Xaa-Thia led to a slight decrease of inhibition of DP IV and POP compared to Xaa-Pyrr and Xaa-Thia, though the inhibition constants were still in the range up to 10(-7) M. As Xaa-Thia exist as two isomers, we investigated isomer specific inhibition with regard to DP IV. Thus, our studies have revealed that DP IV was only inhibited by the Z isomer of the Xaa-psi[CS-N]-Thia. For the first time, Xaa-Pyrr and Xaa-Thia were characterized as inhibitors of DP II with inhibition constants in the micromolar range. In contrast to DP IV inhibition, the Xaa-psi[CS-N]-Pyrr and Xaa-psi[CS-N]-Thia have proven to be more potent inhibitors of DP II than the corresponding Xaa-Pyrr and Xaa-Thia. Thus, these Xaa-psi[CS-N]-Thia are new potent inhibitors especially suitable for DP II with K(i) values ranging in the upper nanomolar concentration.

Cloning, chromosomal sublocalization of the human soluble aminopeptidase P gene (XPNPEP1) to 10q25.3 and conservation of the putative proton shuttle and metal ligand binding sites with XPNPEP2

Human soluble ("cytosolic") aminopeptidase P (hsAmP) is an aminoacylprolyl hydrolase (EC 3.4.11.9) present in all tissues yet examined. hsAmP is related in terms of catalytic specificity to an ectoenzyme, membrane aminopeptidase P (hmAmP), which is largely limited in distribution to endothelia and brush border epithelia. Although both enzymes can degrade oligopeptides having N-terminal Xaa-Pro- moieties, hsAmP and hmAmP are of relatively low sequence homology. Recently, it has been shown that the two enzymes are not products of splice variants of the same gene. How hsAmP relates to hmAmP has clinical significance in that both can inactivate bradykinin, and AmP deficiency states have been described. The hmAmP gene (XPNPEP2) is disposed at chromosome Xq25, a disposition with clear meaning in terms of inheritance of hmAmP deficiencies. To further explore similarities and differences between hsAmP and hmAmP, the present study was begun to determine the chromosomal disposition of the hsAmP gene. Here we show that the gene is sublocalized on chromosome 10q25.3. We also show that hsAmP and hmAmP contain homologous blocks of sequence common to members of the "pita bread-fold" protein family, of which Escherichia coli methionine aminopeptidase is the prototype. The prototype is known to contain a proton shuttle and five divalent metal ligands, counterparts of which we identify in the homologous blocks of sequence in both hsAmP and hmAmP and compare to E. coli aminopeptidase.

Dipeptidyl aminopeptidase IV and aminopeptidase P, two proline specific enzymes from the cytoplasm of guinea-pig brain: their role in metabolism of peptides containing consecutive prolines

In this study the majority of dipeptidyl aminopeptidase IV and aminopeptidase P activities of guinea-pig brain are reported to reside in the cytoplasm. Both activities were purified and soluble dipeptidyl aminopeptidase IV was found to have a relative molecular mass of 194000 and to be comprised of two equal subunits of relative molecular mass 93000 while native soluble aminopeptidase P had a relative molecular mass of 140000. Both activities require proline or alanine in the penultimate position from the N-terminus. Dipeptidyl aminopeptidase IV removed the N-terminal dipeptide whereas aminopeptidase P removed only the N-terminal amino acid. Dipeptidyl aminopeptidase IV was inactive if proline was also present in the third position from the N-terminus whereas aminopeptidase P was unable to remove the N-terminal glycyl, pyroglutamyl or prolyl residues even though proline was present in the second position. Soluble dipeptidyl aminopeptidase IV was differentiated from the previously reported particulate form by its sensitivity to p-chloromercuribenzoate, N-ethyl maleimide and puromycin. The metabolism of Leu-Pro-Pro-Ser by guinea-pig cytoplasm was investigated in the presence of inhibitors to evaluate the contribution by dipeptidyl aminopeptidase IV and aminopeptidase P to the hydrolysis of a peptide containing two consecutive proline residues. The results indicated that either dipeptidyl aminopeptidase IV or prolyl oligopeptidase were required along with aminopeptidase P and prolidase to achieve complete hydrolysis of this tetrapeptide.

Cloning and functional expression of the cytoplasmic form of rat aminopeptidase P

A rat cytoplasmic aminopeptidase P was purified from liver cytosol with a procedure including an affinity elution step with 3 microM inositol 1,3,4-trisphosphate. Proteolytic fragments were generated, sequenced and the enzyme was cloned from a rat liver cDNA library. The structure shows high (87.8% and 95.5%, respectively) sequence identity at the nucleotide and amino acid levels with the previously described human putative cytoplasmic aminopeptidase P. The cloned rat enzyme was functionally expressed in Escherichia coli and also in COS-1 cells. Western blot analysis, using an antibody generated against the recombinant protein, and Northern blot hybridization showed ubiquitous expression of the protein in different tissues with the highest expression level in the testis.