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PubMed1983

Biosynthesis of intestinal microvillar proteins. Pulse-chase labelling studies on maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV.

The biogenesis of three intestinal microvillar enzymes, maltase-glucoamylase (EC 3.2.1.20), aminopeptidase A (aspartate aminopeptidase, EC 3.4.11.7) and dipeptidyl peptidase IV (EC 3.4.14.5), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. The earliest detectable forms of the enzymes were polypeptides of Mr 225000, 140000 and 115000 respectively. These were found to represent the enzymes in a 'high-mannose' state of glycosylation, as judged by their susceptibility to treatment with endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96). After about 40-60 min of chase, maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV were further modified to yield the mature polypeptides of Mr 245000, 170000 and 137000 respectively, which were expressed at the microvillar membrane after 60-90 min of chase. The fact that the enzymes before reaching the microvillar membrane were found in a Ca2+-precipitated membrane fraction (intracellular and basolateral membranes), but not in soluble form, indicates that during biogenesis maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV are transported and assembled in a membrane-bound state.

Acetylglucosaminidase↗

PubMed1997

A tyrosine residue essential for catalytic activity in aminopeptidase A.

Aminopeptidase A (EC 3.4.11.7; APA) is a 130 kDa membrane-bound zinc enzyme that contains the consensus sequence HEXXH (residues 385-389) conserved among the zinc metalloprotease family. In this motif, both histidine residues and the glutamic residue were shown to be involved respectively in zinc co-ordination and catalytic activity. Treatment of APA with N-acetylimidazole results in a loss of enzymic activity; this is prevented by the competitive aminopeptidase inhibitor amastatin, suggesting the presence of an important tyrosine, lysine or cysteine residue at the active site of APA. A tyrosine residue was previously proposed to be involved in the enzymic activity of aminopeptidase N. Furthermore sequence alignment of mouse APA with other monozinc aminopeptidases indicates the presence of a conserved tyrosine (Tyr-471 in APA). The functional role of Tyr-471 in APA was investigated by replacing this residue with a phenylalanine (Phe-471) or a histidine (His-471) residue by site-directed mutagenesis. Kinetic studies showed that the Km values of both mutants were similar to that of the wild-type enzyme, whereas kcat values were decreased by three orders of magnitude and corresponded to a variation in free energy of the rate-limiting step by 4.0 and 4.2 kcal/mol (0.96 and 1.00 kJ/mol) for the Phe-471 and His-471 mutants respectively. The mutation did not modify the inhibitory potency of a thiol-containing inhibitor that strongly chelates the active-site zinc ion, whereas that of a putative analogue of the transition state presumed to mimic the reaction intermediate was reduced. Taken together, these results strongly suggest that the Tyr-471 hydroxy group participates in catalysis by stabilizing the transition state complex through interaction with the oxyanion.

Amino Acid Substitution↗

PubMed1998

A glutamate residue contributes to the exopeptidase specificity in aminopeptidase A.

Aminopeptidase A (EC 3.4.11.7, APA) is a 130 kDa membrane-bound aminopeptidase that contains the consensus sequence HEXXH (385-389) found in the zinc metalloprotease family, the zincins. Sequence alignment of the mouse APA with other monozinc-aminopeptidases indicates the presence of a highly conserved glutamate residue (Glu352 in APA) found in the conserved motif GAMEN (349-353). In monozinc-aminopeptidases, the negative charge of the glutamate side-chain carboxylate may constitute the anionic binding site involved in the recognition of the free amino group of substrates or inhibitors. The functional role of Glu352 in APA was investigated by substituting this residue with an aspartate (Asp352), a glycine (Gly352), a glutamine (Gln352) or an arginine (Arg352) residue by site-directed mutagenesis. Kinetic studies showed that the Km values of the mutant enzymes were unaffected, whereas kcat values were decreased 10-250-fold, resulting in a 10-, 30- 260- and 400-fold reduction in cleavage efficiencies for the mutants Asp352, Gly352, Gln352 and Arg352 respectively. The inhibitory potency of two different classes of inhibitors, a thiol and a phosphonate compound, was significantly (P<0.05) decreased by 10- and 4-fold respectively in the mutated enzymes. Moreover, the inhibitory potency of angiotensin I, used as a competitor of the synthetic substrate alpha-l-glutamyl beta-naphthylamide, displayed a 4-fold reduction (P<0.01) in the mutated enzymes, whereas the Ki values of its N-acetyl derivative were unchanged. These data strongly suggest that Glu352 is involved in the catalytic process of APA and contributes to the exopeptidase activity of this enzyme through interaction with the N-terminal part of substrates or inhibitors.

Amino Acid Sequence↗

PubMed1998

Production and properties of a recombinant soluble form of aminopeptidase A.

Aminopeptidase A is a homodimeric membrane-bound zinc metallopeptidase anchored at the plasma membrane by a 22-amino-acid hydrophobic segment. The anchor segment separates a small N-terminal cytoplasmic domain from a large ectodomain that contains the active site. Site-directed mutagenesis was performed to investigate the role of the cytoplasmic domain of aminopeptidase A in membrane anchoring and routing of the enzyme. Expression in COS-7 cells of a mutant lacking the N-terminal cytoplasmic domain resulted in the efficient secretion of a catalytically active enzyme in the medium. The soluble mutated aminopeptidase A, purified from the medium of a stable cell line, exhibited similar biochemical features to those of the wild-type enzyme. Pulse/chase metabolic labeling experiments revealed that the soluble form is generated intracellularly at an early stage of biosynthesis, suggesting that the signal peptide/membrane anchor domain of aminopeptidase A is removed in the endoplasmic reticulum through the action of the signal peptidase.

Amino Acid Sequence↗

PubMed1999

Lateralization of aminopeptidase A activity in substantia nigra, striatum and frontal cortex of rats.

Several brain aminopeptidase activities have been reported to be asymmetrical, but no direct correlation with lateralized functions has been proposed. Cholecystokinin (CCK) coexists with dopamine (DA) in the nigrostriatal system, which is involved in lateralized motor behaviors. Because aminopeptidase A activity is probably responsible for the hydrolysis of CCK, we studied the left-right distribution of glutamate- (GluAP) and aspartate-aminopeptidase (AspAP) activities in their soluble (Sol) and membrane-bound (M-B) forms in the substantia nigra, striatum and cortex of rats. Although there was a highly significant predominance of the left side in the substantia nigra and striatum for Sol GluAP and M-B AspAP respectively, in the frontal cortex predominance was on the right side for M-B AspAP. These results suggest a relationship between aminopeptidase A activity and lateralized nigro-striato-cortical functions involving CCK.

Aminopeptidases↗

PubMed1991

Aminopeptidase A activity of the murine B-lymphocyte differentiation antigen BP-1/6C3.

The predicted amino acid sequence of the cDNA encoding the murine B-lymphocyte differentiation antigen BP-1/6C3 suggested that it is a member of the zinc-dependent metalloprotease family, possibly an aminopeptidase related to aminopeptidase N [microsomal aminopeptidase; alpha-aminoacyl-peptide hydrolase (microsomal), EC 3.4.11.2]. In the present studies, we examined the enzymatic activity of this antigen. From brush border preparations of the small intestine, a rich source of many endopeptidases and exopeptidases, the BP-1 antibody selectively removed aminopeptidase A [APA; L-alpha-aspartyl(L-alpha-glutamyl)-peptide hydrolase, EC 3.4.11.7] activity. The APA activity of a panel of cell lines correlated in linear fashion with cell-surface levels of the BP-1/6C3 antigen. APA activity was demonstrated for the BP-1/6C3 antigen immunopurified from the pre-B-cell membrane. This activity was enhanced by alkaline earth metals such as Ca2+ and was abrogated by amastatin and angiotensin, which are known competitive inhibitors of APA. The data indicate that the murine BP-1/6C3 antigen is active APA, an enzyme that catalyzes specifically the removal of unsubstituted, N-terminal glutamic acid and aspartic acid residues from peptides.

Aminopeptidases↗

PubMed2001

Genomic organization of the human adipocyte-derived leucine aminopeptidase gene and its relationship to the placental leucine aminopeptidase/oxytocinase gene.

The genomic organization of the gene encoding the human adipocyte-derived leucine aminopeptidase (A-LAP) has been determined. The gene is composed of 20 exons and 19 introns and spans approximately 47 kilobases of chromosome 5q15. The gluzincin aminopeptidase motif, the HEXXH(X)(18)E zinc-binding motif essential for enzymatic activity, is encoded by exons 6 and 7. A comparison of the exon/intron boundaries, together with phylogenetic analysis, shows the close relationship between A-LAP and placental leucine aminopeptidase (P-LAP)/oxytocinase, another gluzincin aminopeptidase considered to be important for the maintenance of normal pregnancy. Primer extension analysis revealed two transcriptional initiation sites. Analysis of the sequence immediately upstream of the transcriptional initiation sites revealed that the A-LAP promoter contains no canonical TATA- or CCAAT-box, but has a PyPyA(+1)N(T/A)PyPy initiator consensus sequence and multiple putative regulatory elements. Finally, luciferase-reporter assays revealed a functional promoter activity of the 5'-flanking region of the gene, and suggested that the activity is regulated in a cell type-specific manner.

Adipocytes↗

PubMed1980

Aminopeptidases highly specific for glutamyl residues from Neisseria meningitidis and Moraxella urethralis.

Cell-associated glutamyl aminopeptidase activity was detected in several strains of Neisseria meningitidis and Moraxella urethralis grown in liquid culture. Enzymatic activity was released from washed cells by ultrasonic treatment and monitored fluorometrically by measuring the release of aryl groups from 17 different aminoacyl-beta-naphthylamides. Substrates containing a glutamyl moiety were readily hydrolyzed by both N. meningitidis and M. urethralis. Glutamyl aminopeptidase activity was partially purified from crude sonicates by means of ion-exchange and gel chromatography, and samples were examined by polyacrylamide gel electrophoresis. Kinetic and pH studies were performed to partially characterize activities. The molecular weight of the M. urethralis enzyme was approximately 88,000, whereas the apparent molecular weight of the N. meningitidis enzyme was shown to be in excess of 200,000. M. urethralis produced two glutamyl aminopeptidases, one specific for a gamma-glutamyl moiety, the other specific for an alpha-glutamyl moiety. In contrast, N. meningitidis produced a single glutamyl aminopeptidase which hydrolyzed alpha- and gamma-glutamyl-substituted beta-naphthylamides.

Aminopeptidases↗

PubMed1986

Serum leucine aminopeptidase for monitoring viral infections with plasmacytoid reaction.

Analysis of data on 9 cases with active cytomegalovirus infection in patients with kidney grafts showed a positive association of serum leucine aminopeptidase activity concentration with the appearance of plasmacytoid lymphocytes in blood. Additional studies indicate that like the liver, the lymphocytes contain leucine aminopeptidase in relatively large quantities and that this enzyme is increased about 3-fold in plasmacytoid lymphocytes when compared with the activity in normal lymphocytes. In contrast, the 'hepatic' enzyme alanine aminotransferase is practically absent in both lymphocytes and plasmacytoid cells. Therefore, the difference in serum between the relative increases of leucine aminopeptidase and alanine aminotransferase may be attributed to proliferating plasmacytoid lymphocytes. Earlier observations on a large number of cases of acute viral hepatitis A or B lend credence to this assumption. However, in this disease, the serum enzyme changes reflect the much greater involvement of the liver and the relatively slight, but significant, proliferation of plasmacytoid lymphocytes. Our hypothesis is confirmed by the recent observation of 3 cases of acute EBV infection (infectious mononucleosis) in otherwise healthy individuals showing greatly elevated leucine aminopeptidase in contrast to normal or slightly raised alanine aminotransferase in serum.

Adult↗

PubMed2005

The two authentic methionine aminopeptidase genes are differentially expressed in Bacillus subtilis.

BACKGROUND: Two putative methionine aminopeptidase genes, map (essential) and yflG (non-essential), were identified in the genome sequence of Bacillus subtilis. We investigated whether they can function as methionine aminopeptidases and further explored possible reasons for their essentiality or dispensability in B. subtilis. RESULTS: In silico analysis of MAP evolution uncovered a coordinated pattern of MAP and deformylase that did not correlate with the pattern of 16S RNA evolution. Biochemical assays showed that both MAP (MAP_Bs) and YflG (YflG_Bs) from B. subtilis overproduced in Escherichia coli and obtained as pure proteins exhibited a methionine aminopeptidase activity in vitro. Compared with MAP_Bs, YflG_Bs was approximately two orders of magnitude more efficient when assayed on synthetic peptide substrates. Both map and yflG genes expressed in multi-copy plasmids could complement the function of a defective map gene in the chromosomes of both E. coli and B. subtilis. In contrast, lacZ gene transcriptional fusions showed that the promoter activity of map was 50 to 100-fold higher than that of yflG. Primer extension analysis detected the transcription start site of the yflG promoter. Further work identified that YvoA acted as a possible weak repressor of yflG expression in B. subtilis in vivo. CONCLUSION: Both MAP_Bs and YflG_Bs are functional methionine aminopeptidases in vitro and in vivo. The high expression level of map and low expression level of yflG may account for their essentiality and dispensality in B. subtilis, respectively, when cells are grown under laboratory conditions. Their difference in activity on synthetic substrates suggests that they have different protein targets in vivo.

Aminopeptidases↗

PubMed2004

Role of the insulin-regulated aminopeptidase IRAP in insulin action and diabetes.

The insulin-regulated aminopeptidase (IRAP) is a member of the family of zinc-dependent membrane aminopeptidases. It is the homolog of the human placental leucine aminopeptidase (P-LAP). IRAP is expressed in different cell types but has been best characterized in two major insulin target cells, muscle and fat. In these cells IRAP localizes to intracellular membrane compartments under basal conditions. In response to insulin IRAP redistributes to the cell surface. IRAP shares this behavior with the insulin-responsive glucose transporter GLUT4. It is established that insulin's dramatic effect on glucose disposal is mediated through its action on GLUT4. The role IRAP plays in insulin action is unknown. IRAP cleaves several peptide hormones in vitro. In insulin-treated cells, concomitant with the appearance of IRAP at the cell surface, aminopeptidase activity toward extracellular substrates increases. Thus, insulin, by bringing IRAP to the cell surface, could increase the processing of extracellular peptide hormones and thereby change their activities. Investigations are underway to determine the in vivo substrates for IRAP and to measure the effect of insulin on the cleavage of identified substrates. In individuals with type 2 diabetes the insulin-stimulated translocation of IRAP to the cell surface of muscle and fat cells is impaired. This defect may lead to decreased cleavage and consequently increased action of peptide hormones that are substrates for IRAP. Impaired IRAP action may thus play a role in the development of complications in type 2 diabetes. The findings of decreased expression of GLUT4 and increased heart size in mice in which IRAP was deleted support this hypothesis.

Amino Acid Sequence↗

PubMed2004

Membrane bound members of the M1 family: more than aminopeptidases.

In mammals the M1 aminopeptidase family consists of nine different proteins, five of which are integral membrane proteins. The aminopeptidases are defined by two motifs in the catalytic domain; a zinc binding motif HEXXH-(X18)-E and an exopeptidase motif GXMEN. Aminopeptidases of this family are able to cleave a broad range of peptides down to only to a single peptide. This ability to either generate or degrade active peptide hormones is the focus of this review. In addition to their capacity to degrade a range of peptides a number of these aminopeptidases have novel functions that impact on cell signalling and will be discussed.

Aminopeptidases↗

PubMed1991

Aminopeptidases and angiotensin I-converting enzyme activities in primary human lung tumors and lung parenchyma.

The activities of alanyl aminopeptidase (AAP), arginyl aminopeptidase (RAP), alpha-glutamyl aminopeptidase (EAP) and angiotensin I-converting enzyme (ACE) were investigated in primary human lung tumors of different histological types and in matched lung parenchyma. In contrast to the studied aminopeptidases whose activity differences between tumor and lung tissues were infrequently significant, the activity of ACE was decreased highly significantly in the majority of lung tumors.

Adenocarcinoma↗

PubMedDate not supplied

Increase of methionine-aminopeptidase activity in hyperplastic Leydig cells of rat cryptorchid testis.

In order to elucidate the reasons for the increased methionine-aminopeptidase activity in the rat cryptorchid testis, a histochemical study was conducted on the changes in testicular aminopeptidase activities using various substrates after the cryptorchidism experimentally was induced with reference to the regenerated hepatic cells which appeared in the partially hepatectomized liver of rat. Methionine-aminopeptidase gradually increased in Leydig cells after cryptorchid was induced, whereas the enzyme activity decreased in regenerated hepatic cells. These histochemical observations were coincident with the data obtained by enzyme assay. The present study has clearly indicated that the increased methionine aminopeptidase activity was specific for hyperplastic and hypertrophic Leydig cells in the cryptorchid testis, but did not depend merely on cell hyperplasia.

Aminopeptidases↗

PubMedDate not supplied

[Aminopeptidase system of Aspergillus flavus].

The aminopeptidases system contained in a complex of exocellular peptidhydrolases synthetized by Asp. flavus was studied. Separation of the system into individual enzymes of the type of leucin aminopeptidase, aminotripeptidase and specific leucyl-glycyl-glycine-aminopeptidase by the methods of salt fractionation. DEAE-Sephadex A-50 and DEAE-cellulose chromatography. These enzymes are characterized by a different degree of purification as well as by the presence of the multiple forms, anion and cation ones. The multiple forms differ in solubility, specific activity, chromatographic properties, thermostability. The presence of individual triglycine-aminotripeptidase is shown in the system. The differences are found in the properties of the enzymes splitting leucinamide and leucyl-glycine. There may be two different leucine aminopeptidases. Studies in correlation during hydrolysis of leucinamide and leucyl-glycyl-glycine and comparison of the fractions properties displaying the activities showed that there are no reasons to ascribe these both reactions to the effect of the same enzyme.

Aminopeptidases↗

PubMed1982

[Leucine and alanine aminopeptidase activity in the organs of cattle, sheep and swine].

Studied was the activity of leucine-aminopeptidase and alanine-aminopeptidase in fresh tissue homogenates of liver, spleen, kidney, heart, pancreas, femoral muscle, stomach (rumen), small intestine, and lung taken from 8 cattle, sheep, and pigs. Both enzymes showed ubiquity. Leucine-aminopeptidase exhibited highest activity in the spleen of pigs and the kidney of sheep and cattle. The kidneys of all investigated animal species showed 10 to 15 times higher alanine-aminopeptidase activity than the remaining organs. This pointed to the relative ubiquity of the enzyme with special reference to kidneys.

Aminopeptidases↗

PubMed1994

Potential indirect anti-inflammatory effects of IL-4. Stimulation of human monocytes, macrophages, and endothelial cells by IL-4 increases aminopeptidase-N activity (CD13; EC 3.4.11.2).

IL-4 up-regulates various monocytic properties that are associated with pro-inflammatory functions. Paradoxically, IL-4 may also act as an anti-inflammatory agent by down-regulating the production of several inflammatory mediators. As the activity of some mediators has recently been shown to be regulated by peptidases, we examined whether IL-4 was able to modulate the expression of a cell membrane-associated peptidase, aminopeptidase-N (CD13). IL-4 caused a dose-dependent increase in the expression of CD13 Ag on highly purified human blood monocytes. Maximal expression was observed around 48 h of culture. This IL-4-induced increase was completely blocked by anti-IL-4 antiserum. Furthermore, the increase in surface expression was preceded by increased mRNA levels of CD13, which was maximal around 24 h of culture. We also observed that CD13-mediated leucine-aminopeptidase activity of monocytes was induced by IL-4. Other CD13-expressing cells were also sensitive to IL-4, as CD13 Ag expression and CD13 mRNA levels were up-regulated in human alveolar macrophages and endothelial cells upon IL-4 treatment. The increased expression of cell membrane aminopeptidase-N represents a potentially increased cellular ability to inactivate inflammatory mediators. Therefore, these findings represent further evidence of IL-4-mediated anti-inflammatory actions. We postulate that up-regulation of aminopeptidase-N expression may be an indirect mechanism of IL-4 to modulate the action of bioactive peptides. This mechanism may underlie, at least partially, the anti-inflammatory effects of IL-4 in vivo.

Aminopeptidases↗

PubMed2002

Purification and properties of phenylalanyl aminopeptidase synthesised by Pseudomonas sp.

Intracellular aminopeptidase synthesized by a soil strain of Pseudomonas sp. was purified 323-fold using the following procedure: saturation with ammonium sulfate, separation by preparative electrophoresis, anion-exchange chromatography and gel filtration chromatography. Molecular weight of the enzyme determined according to the latter method was 57 kDa. Aminopeptidase showed a high substrate specificity and affinity to Phe-beta-naphtylamide (Phe-beta-NA) as a substrate. A considerable inhibition of the enzymatic activity by iodoacetamide and p-chloromercuribenzoate (p-CMB) led to the conclusion that it was a cysteine aminopeptidase. Hydrosulphide compounds markedly stabilised the enzyme. Ethylenediaminetetra-acetic acid (EDTA), a metalloenzyme inhibitor, caused a double increase in the phenylalanyl aminopeptidase activity.( )Mg(2+) ions activated the enzyme to a negligible extent, whereas Co(2+), Cu(2+), Cd(2+) and Pb(2+) ions contributed to its inhibition. The highest enzymatic activity was observed at 37 degrees C and pH 7.0.

2-Naphthylamine↗