Specificity of the wound-induced leucine aminopeptidase (LAP-A) of tomato activity on dipeptide and tripeptide substrates.

Wounding of tomato leaves results in the accumulation of an exoprotease called leucine aminopeptidase (LAP-A) that preferentially hydrolyzes amino acid-p-nitroanilide and -beta-naphthylamide substrates with N-terminal Leu, Met and Arg residues. To determine the substrate specificity of LAP-A on more natural substrates, the rates of hydrolysis of 60 dipeptide and seven tripeptide substrates were determined. For comparison, the specificities of the porcine and Escherichia coli LAPs were evaluated in parallel. Several marked differences in substrate specificities for the animal, plant and prokaryotic LAP enzymes were observed. Substrates with variable N-terminal (P1) residues (Xaa) were evaluated; these substrates had Leu or Gly in the penultimate (P1') position. The plant, animal, and prokaryotic LAPs hydrolyzed dipeptides with N-terminal nonpolar aliphatic (Leu, Val, Ile, and Ala), basic (Arg), and sulfur-containing (Met) residues rapidly, while P1 Asp or Gly were cleaved inefficiently from peptides. Significant differences in the cleavage of dipeptides with P1 aromatic residues (Phe, Tyr, and Trp) were noted. To systematically evaluate the impact of the P1' residue on cleavage of dipeptides, three series of dipeptides (Leu-Xaa, Gly-Xaa, and Arg-Xaa) were evaluated. The P1' residue strongly influenced hydrolysis of dipeptides and the magnitude of its effect was dependent on the P1 residue. P1' Pro, Asp, Lys and Gly slowed the hydrolysis rates of the tomato LAP-A, porcine LAP, and E. coli PepA markedly. Analysis six Arg-Gly-Xaa tripeptides showed that more diversity was tolerated in the P2' position. P2' Arg inhibited tripeptide cleavage by all three enzymes, while P2' Asp enhanced hydrolysis rates for the porcine and prokaryotic LAPs.     

Aminopeptidases in webbing clothes moth larvae. properties and specificities of enzymes of highest electrophoretic mobility.

The group of aminopeptidase bands from Tineola bisselliella larvae with highest electrophoretic mobility in polyacrylamide gels were purified further and partially separated by ion exchange chromatography. Three aminopeptidase bands were present in this material and were very similar with respect to their pH optima (7-7), their molecular weight of 94,000, their responses to metal ions and enzyme inhibitors and in their substrate specificity requirements. Kinetic constants were obtained for the hydrolysis of 17 different alpha-aminoacyl-beta-naphthylamides by these aminopeptidases, the most favoured substrates being the derivatives of alanine, methionine, proline, leucine, glycine, glutamic acid, lysine and arginine. The enzymes also hydrolyse amino acid amides, dipeptides, dipeptide amides, tripeptides and oligopeptides at the N-terminal end. These enzymes differ from the other aminopeptides in T. bisselliella in being able to hydrolyse bonds involving proline.     

Isolation and characterization Salmonella typhimurium mutants lacking a tripeptidase (peptidase T).

Salmonella typhimurium contains an enzyme, peptidase T, that hydrolyzes a variety of tripeptides. Specificity studies with a peptidase activity stain after gel electrophoresis of crude cell extracts showed that peptidase T hydrolyzes tripeptides containing N-terminal methionine, leucine, or phenylalanine. Little or no activity could be detected against dipeptides, N-blocked or C-blocked tripeptides, and tetrapeptides. Analysis of reaction products by high-pressure liquid chromatography showed that peptidase T removes the N-terminal amino acid from tripeptides. Mutants lacking peptidase T were isolated by screening microcultures grown in the wells of plastic microtitration plates for hydrolysis of Met-Ala-Ser or Met-Gly-Gly. Mutations (pepT) that eliminate this enzyme were found to be phage P22 cotransducible with purB at approximately 25 map units on the S. typhimurium map. Comparison of the growth properties of mutant and wild-type strains suggests that peptidase T does not function in utilization of tripeptides to provide amino acids during growth.     

Isolation, purification and investigation of physico-chemical properties and specificity of Leu-Gly-Gly-amino peptidase]

A highly purified (237-fold) preparation of extracellular Leu-Gly-Gly aminopeptidase was isolated from the 716 strain of mould Aspergillis flavus. The enzyme was found electrophoretically and enzymatically homogeneous, using Leu-beta-naphthylimide as substrate. The pH optimum is 8.60; the temperature optimum is about 50 degrees C. The enzyme was inhibited by EDTA and completely reactivated by Co2+ ions; Ca2+ and Mn2+ ions considerably restored the enzyme activity. The enzyme showed the optimal activity during the cleavage of substrates, containing N-terminal leucine. Mild hydrolysis of leucine-free tripeptides and dipeptides with N-terminal glycine and alanine was observed. The enzyme was found to be stereospecific in some respects. Peptides with a blocked terminal NH2-group are not hydrolyzed by the enzyme.     

Aminopeptidase N from Streptococcus salivarius subsp. thermophilus NCDO 573: purification and properties

A 96 kDa aminopeptidase was purified from Streptococcus salivarius subsp. thermophilus NCDO 573. The enzyme had similar properties to aminopeptidases isolated from lactococci and lactobacilli and showed a high degree of N -terminal amino acid sequence homology to aminopeptidase N from Lactococcus lactis subsp. cremoris. It catalysed the hydrolysis of a range of aminoacyl 4-nitroanilides and 7-amido-4-methylcoumarin derivatives, dipeptides, tripeptides and oligopeptides. In common with aminopeptidases from other lactic acid bacteria, the enzyme from Strep. salivarius subsp. thermophilus showed highest activity with lysyl derivatives but was also very active with arginyl and leucyl derivatives. Relative activity with alanyl, phenylalanyl, tyrosyl, seryl and valyl derivatives was considerably lower and with glycyl, glutamyl and prolyl derivatives almost negligible. The aminopeptidase also catalysed the hydrolysis of dipeptides and tripeptides but mostly at rates much less than that with L-lysyl-4-nitroanilide and oligopeptides. The enzyme catalysed the successive hydrolysis of various amino acid residues from the N -terminus of several oligopeptides but it was unable to cleave peptide bonds on the N -terminal side of a proline residue.     

Structure and activity of angiotensin I converting enzyme inhibitory peptides derived from Alaskan pollack skin

Angiotensin I that converts the enzyme (ACE) inhibitory peptide, Gly-Pro-Leu, previously purified and identified from the Alaskan pollack skin gelatin hydrolysate, were synthesized. In addition, the peptides Gly-Leu-Pro, Leu- Gly-Pro, Leu-Pro-Gly, Pro-Gly-Leu, Pro-Leu-Gly, Gly- Pro, and Pro-Leu, which consisted of glycine, proline, and leucine, were synthesized by the solid-phase method. The IC50 values of each tripeptide. namely Leu-Gly-Pro, Gly- Leu-Pro, Gly-Pro-Leu, Pro-Leu-Gly, Leu-Pro-Gly, and Pro-Gly-Leu. were 0.72, 1.62, 2.65, 4.74, 5.73, and 13.93 microM, respectively. The ACE inhibitory activity of these tripeptides was higher than that of dipeptides, such as Gly- Pro and Pro-Leu with IC50 values of 252.6 and 337.3 microM, respectively. Among the tripeptides, Leu-Gly-Pro and Gly- Leu-Pro had higher inhibitory activity than Gly-Pro-Leu that was isolated from the Alaskan pollack skin gelatin hydrolysate. Among the different types of tripeptides that were examined, the highest ACE inhibitory activity was observed for Leu-Gly-Pro. It had the leucine residue at the N-terminal and proline residue at the C-terminal.     

Histidines 345 and 378 of <Emphasis Type="Italic">Bacillus stearotheromophilus</Emphasis> leucine aminopeptidase II are essential for the catalytic activity of the enzyme

The conserved histidine residues, His-191, His-227, His-345, and His-378, in Bacillus stearothermophilus leucine aminopeptidase II (LAPII) were replaced with leucine by site-directed mutagenesis. The overexpressed wild-type and mutant enzymes have been purified by nickel-chelate chromatography and their molecular masses were approximately 44.5 kDa. Under assay conditions, no LAP activity was detected in H345L and H378L. Although the K_m value for H191L increased more than 30% with respect to the wild-type LAPII, alteration in this residue did not lead to a significant change on the catalytic efficiency. The 39% decrease in K_cat/K_m for H227L was partly caused by a 3.9-fold increase in K_m value. Based on these results, it is suggested that His-345 and His-378 play a crucial role in the catalytic reaction of B. stearothermophilus LAPII.     

Peptidase-deficient mutants of Escherichia coli.

Mutant derivatives of Escherichia coli K-12 deficient in several peptidases have been obtained. Mutants lacking a naphthylamidase, peptidase N, were isolated by screening for colonies unable to hydrolyze L-alanine beta-naphthylamide. Other mutants were isolated using positive selections for resistance to valine peptides. Mutants lacking peptidase A, a broad-specificity aminopeptidase, were obtained by selection for resistance to L-valyl-L-leucine amide. Mutants lacking a dipeptidase, peptidase D, were isolated from a pepN pepA strain by selection for resistance to L-valyl-glycine. Starting with a pepN pepA pepD strain, selection for resistance to L-valyl-glycyl-glycine or several other valine peptides produced mutants deficient in another aminopeptidase, peptidase B. Mutants resistant to L-valyl-L-proline lack peptidase Q, an activity capable of rapid hydrolysis of X-proline dipeptides. Using these selection procedures, a strain (CM89) lacking five different peptidases has been isolated. Although still sensitive to valine, this strain is resistant to a variety of valine di- and tripeptides. The ability of this strain to use peptides as sources of amino acids is much more restricted than that of wild-type E. coli strains. Strains containing only one of the five peptidases missing in CM89 have been constructed by transduction. The peptide utilization profiles of these strains show that each of the five peptidases can function during growth in the catabolism of peptides.     

Comparative characteristics of soluble and membrane brain aminopeptidases. II. Substrate specificity

Comparative studies on substrate specificity of the soluble and membrane-bound aminopeptidases from bovine brain were carried out. A series of p-nitroanilides and beta-naphthylamides of amino acids, di- and tripeptides with the aminoterminal phenylalanine residue, as well as a biologically active pentapeptide--[Leu5]enkephalin--were used as substrates. The soluble and membrane-bound aminopeptidases manifested identical specificity towards the employed substrates. The aminopeptidases were equally effective towards the p-nitroanilides of amino acids and peptides, whereas beta-naphthylamides were more susceptible to hydrolysis by both aminopeptidases than p-nitroanilides and peptides. Taking into account physico-chemical characteristics of these enzymes, it was concluded that the soluble and membrane-bound aminopeptidases are quite similar or perhaps identical. Their role in the regulation of nervous system functioning was discussed. A comparison of specificities for brain aminopeptidases and leucine aminopeptidase from bovine lens led to the conclusion that they belong to different groups. This feature allows planning the synthesis of selective inhibitors.     

Enzymatic digestibility of peptides cross-linked by ionizing radiation

p6gestibility by proteolytic enzymes of peptides cross-linked by ionizing radiation was investigated. Small peptides of alanine and phenylalanine were chosen as model compounds and aminopeptidases and carboxypeptidases were used as proteolytic enzymes. Peptides exposed to gamma-radiation in aqueous solution were analysed by high-performance liquid chromatography before and after hydrolysis by aminopeptidase M, leucine aminopeptidase, carboxypeptidase A and carboxypeptidase Y. The results obtained clearly demonstrate the different actions of these enzymes on cross-linked aliphatic and aromatic peptides. Peptide bonds of cross-linked dipeptides of alanine were completely resistant to enzymatic hydrolysis whereas the enzymes, except for carboxypeptidase Y, cleaved all peptide bonds of cross-linked peptides of phenylalanine. The actions of the enzymes on these particular compounds are discussed in detail.     

Directed Mutagenesis of the Conserved Asparagine Residues of Bacillus Stearothermophilus Leucine Aminopeptidase II

Summary To understand the structure–function relationships of Bacillus stearothermophilus leucine aminopeptidase II (LAPII), each of the four conserved asparagine residues was replaced with leucine, aspartate, and lysine respectively by site-directed mutagenesis. The over-expressed wild-type and mutant enzymes with an apparent molecular mass of approximately 44.5 kDa were purified to homogeneity by nickel-chelate chromatography. Substitution of Asn-245, Asn-335, and Asn-341 with Lys generated variants with a dramatic loss of LAP activity. Kinetic analysis of Asn-373 variants with p-leucine-nitroanilide as the substrate revealed an increase in k_cat with no significant change in K_m, leading to a more than 2-fold increase in the catalytic efficiency. Thermostability assays showed that replacement of Asn-335, Asn-341, and Asn-373 by aspartic acid markedly increased the half-life of the enzyme at 70 °C, indicating that the deamination of these residues may have a deleterious effect on LAPII.     

Purification and characterization of a cell wall peptidase from Lactococcus lactis subsp. cremoris IMN-C12.

A peptidase from the cell wall fraction of Lactococcus lactis subsp. cremoris IMN-C12 has been purified to homogeneity by hydrophobic interaction chromatography, two steps of anion-exchange chromatography, and gel filtration. The molecular mass of the purified enzyme was estimated to be 72 kDa by gel filtration and 23 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme has a pI of 4.0, and it has the following N-terminal sequence from the 2nd to the 17th amino acid residues: -Arg-Leu-Arg-Arg-Leu-?-Val-Pro-Gly-Glu-Ileu-Val-Glu-Glu-Leu-Leu. The peptidase is most active at pH 5.8 and at 33 degrees C with trileucine as the substrate. Reducing agents such as dithiothreitol, beta-mercaptoethanol, and cysteine strongly stimulated enzyme activity, while p-chloromercuribenzoate had an inhibitory effect. Also, metal chelators lowered the peptidase activity, which could not be restored with Ca2+ and Mg2+. The divalent cations Cu2+, Zn2+, Fe2+, and Hg2+ completely inhibited peptidase activity. The peptidase is capable of hydrolyzing tripeptides and some dipeptides, with a preference for peptides containing leucine and with the highest activity towards the tripeptides Leu-Leu-Leu, Leu-Trp-Leu, and Ala-Leu-Leu, which were hydrolyzed with Kms of 0.37, 0.18, and 0.61 mM, respectively.     

Novel and highly sensitive fluorescent assay for leucine aminopeptidases

l-Leucine aminopeptidases (LAPs) are implicated in the progress of many pathological disorders and play some regulatory roles in tumor cell proliferation, invasion, and/or angiogenesis. Thus, LAPs not only could become new diagnostic or prognostic biomarkers but also may have potential as novel molecular targets for the treatment of several cancers. Highly sensitive assays are critical for early detection of changes in LAP activity and for screening potent LAP inhibitors. In this study, we developed a novel and highly sensitive fluorescent assay for LAPs based on substituted aminopyridines as fluorescent reporters. This assay was at least 100- and 20-fold more sensitive than commercial colorimetric and fluorescent LAP substrates, respectively. We also showed that this assay was a useful tool for monitoring LAP activities in extracts from cancer cell lines, as well as for the high-throughput screening of inhibitors, which could lead to new cancer treatments.     

Studies on ox brain aminopeptides

1. Mn(2+)-inhibited and Mn(2+)-activated aminopeptidases have been observed in ox brain and separated from one another by DEAE-cellulose column chromatography. 2. The Mn(2+)-inhibited enzyme has been purified 36-fold; it exhibits a specificity for tripeptide substrates, whereas the Mn(2+)-activated aminopeptidase cleaves dipeptides as well as tripeptides. 3. Ammonium sulphate treatment generates a Mn(2+)-stimulated aminopeptidase that is stable to dialysis against EDTA and water, in contrast with an endogenous Mn(2+)-activated preparation that is irreversibly denatured by such dialysis against EDTA and water.     

Soluble di- and aminopeptidases in Escherichia K-12. Dispensible enzymes.

As part of a study of the peptidase content of Escherichia coli K-12, two peptidase-deficient amino acid auxotrophs isolated and characterized by Miller as pepD- (strain CM17) and pepD- pepN- pepA- pepB- pepQ- (strain CM89) were examined for the presence of several peptidases previously obtained from strain K-12 in this laboratory. The soluble fraction of each mutant was found to lack the broad-specificity strain K-12 dipeptidase DP and the strain CM89 fraction also lacked activity characteristic of the strain K-12 aminopeptidases AP, L, and OP; like strain CM17, strain CM89 contained the tripeptide-specific aminopeptidase TP. Strain CM89 (but not CM17) appeared to contain little if any activity attributable to the ribosome-bound aminopeptidase I of strain K-12. Whereas loss of DP, AP, OP, and aminopeptidase I activity may be attributed to the pepD-, pepB-, pepN-, and pepA- mutations, respectively, the reason for the loss of L activity remains uncertain. Grown responses of strain CM89 in liquid media containing di- or tripeptides were in accord with absence of enzymes catalyzing rapid hydrolysis of dipeptides. In synthetic liquid media supplemented with the required amino acids per se or with peptone, cultures of both CM strains grew more slowly than strain K-12 and produced smaller cell-yields than those produced by strain K-12.     

Purified gamma-glutamyl transpeptidases from tomato exhibit high affinity for glutathione and glutathione S-conjugates

gamma-Glutamyl transpeptidases (gammaGTases) are the only enzymes known to hydrolyze the unique N-terminal amide bonds of reduced glutathione (gamma-L-glutamyl-cysteinyl-glycine), oxidized glutathione, and glutathione S-conjugates. Two gammaGTases (I and II) with K(m) values for glutathione of 110 and 90 microM were purified 2,977-fold and 2,152-fold, respectively, from ripe tomato (Lycopersicon esculentum) pericarp. Both enzymes also hydrolyze dipeptides and other tripeptides with N-terminal, gamma-linked Glu and the artificial substrates gamma-L-glutamyl-p-nitroanilide and gamma-L-glutamyl(7-amido-4-methylcoumarin). They transfer the glutamyl moiety to water or acceptor amino acids, including L-Met, L-Phe, L-Trp, L-Ala, or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. gammaGTase I and II were released from a wall and membrane fraction of a tomato fruit extract with 1.0 M NaCl, suggesting that they are peripheral membrane proteins. They were further purified by acetone precipitation, Dye Matrex Green A affinity chromatography, and hydrophobic interaction chromatography. The two gammaGTases were resolved by concanavalin A (Con A) affinity chromatography, indicating that they are differentially glycosylated. The native and SDS-denatured forms of both enzymes showed molecular masses of 43 kD.     

The subcellular localization of di- and tri-peptide hydrolase activity in guinea-pig small intestine

1. Two different subcellular fractionation techniques were applied to guinea-pig intestinal mucosa and the composition of the brush borders prepared by the two methods were compared. 2. By using a kinetic assay system the subcellular distribution of activity against ten dipeptides and five tripeptides was studied. 3. Only small amounts (5–10%) of activity against dipeptides were found in the brush-border region, the enzymes being concentrated in the cytosol. 4. Significant amounts (10–60%) of activity against tripeptides were found in the brush border with the remainder largely present in the soluble fraction. 5. The relevance of these studies to the localization in vivo and the possible role of peptidases in protein digestion is discussed.     

Proteinases in growth and spore formation of Bacillus thuringiensis]

Some serine proteases and leucine aminopeptidases were detected inside and outside the cells during the analysis of three crystalline and two acrystalline strains of Bac. thuringiensis var. galleriae. The data obtained on the protease formation during growth and sporulation and the level of their activity are indicative of intracellular proteases involvement in spore- and crystal formation. The enzymes isolated from the culture medium do not probably take part in these processes. The intracellular enzymes may account for the different crystal protein composition of various strains due to limited proteolysis of crystal proteins in the course of biosynthesis.     

Inactivation of Bacillus stearothermophilus Leucine Aminopeptidase II by Hydrogen Peroxide and Site-Directed Mutagenesis of Methionine Residues on the Enzyme

Leucine aminopeptidases (LAPs) are exopeptidases that remove the N-terminal L-leucine from peptide substrates. Oxidative stability assay showed that the recombinant Bacillus stearothermophilus LAP II (rLAPII) was sensitive to oxidative damage by hydrogen peroxide at the elevated temperature. The H2O2-treated enzyme experienced obvious changes in the secondary structure when the oxidant concentration increased to 300 mM. To investigate the role of methionine residues on the oxidative inactivation, each of the five methionine residues in the rLAPII was replaced with leucine by site-directed mutagenesis. The mutant enzymes with an apparent Mr of approximately 44.5 kDa were overexpressed in Escherichia coli and were purified to homogeneity by nickel-chelate chromatography. The specific activities for Met82Leu, Met88Leu, Met254Leu, and Met382Leu were similar to that of the wild-type enzyme, whereas a reduced activity was observed in Met136Leu. The 50% decrease in the catalytic efficiency (kcat/Km) for Met136Leu was caused by 47% decrease in kcat value. As compared with the wild-type enzyme, all mutant proteins were more sensitive to the oxidant, implying that the methionine residues of B. stearothermophilus LAP II are important for the protection of the enzyme from oxidative inactivation.