Purification and characterisation of leukotriene A4 hydrolase from rat neutrophils

Leukotriene A4 hydrolase was rapidly and extensively purified from rat neutrophils using anion exchange and gel filtration high-pressure liquid chromatography. The enzyme which converts the allylic epoxide leukotriene A4 to the 5,12-dihydroxyeicosatetraenoic acid leukotriene B4 was localized in the cytosolic fraction and exhibited an optimum activity at pH 7.8 and an apparent Km for leukotriene A4 between 2 X 10(-5) and 3 X 10(-5) M. The purified leukotriene A4 hydrolase was shown to have a molecular weight of 68 000 on sodium dodecylsulfate polyacrylamide gel electrophoresis and of 50 000 by gel filtration. The molecular weight and monomeric native form of this enzyme are unique characteristics which distinguish leukotriene A4 hydrolase from previously purified epoxide hydrolases.     

Purification and characterization of human microsomal dipeptidase

Human microsomal dipeptidase (MDP, formerly referred to as dehydropeptidase-I or renal dipeptidase) [EC 3.4.13.11] was solubilized from the membrane fraction of kidney by treatment with octyl-beta-D-glucoside and purified by a procedure including ion exchange chromatography and affinity chromatography on cilastatin-immobilized Sepharose. The purified human MDP was found to be homogeneous on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The apparent molecular weight (Mr) was estimated by SDS-polyacrylamide gel electrophoresis under non-reducing conditions to be 130 kDa, comprising a homodimer of two subunits. After treatment with endoglycosidase F, human MDP showed a single band with an apparent Mr of 42 kDa on SDS-polyacrylamide gel electrophoresis. Human MDP was found to bind to Con A-Sepharose and the activity was eluted with methyl-alpha-D-mannopyranoside, suggesting that human MDP is a glycoprotein. We also examined the substrate specificity of human MDP and found that human MDP catalyzed the hydrolysis of S(substituent)-L-cysteinyl-glycine adducts such as L-cystinyl-bis(glycine) and S-N-ethylmaleimide-L-cysteinyl-glycine, as well as the conversion of leukotriene D4 to leukotriene E4. These results suggest that MDP might play an important role in the metabolism of glutathione and leukotriene.     

Purification and characterisation of leukotriene A4 hydrolase from rat neutrophils

Leukotriene A₄ hydrolase was rapidly and extensively purified from rat neutrophils using anion exchange and gel filtration high-pressure liquid chromatography. The enzyme which converts the allylic epoxide leukotriene A₄ to the 5,12-dihydroxyeicosatetraenoic acid leukotriene B₄ was localized in the cytosolic fraction and exhibited an optimum activity at pH 7.8 and apparent K_m for leukotriene A₄ between 2 · 10^?5 and 3 · 10^?5 M. The purified leukotriene A₄ hydrolase was shown to have a molecular weight of 68 000 on sodium dodecylsulfate polyacrylamide gel electrophoresis and of 50 000 by gel filtration. The molecular weight and monomeric native form of this enzyme are unique characteristics which distinguish leukotriene A₄ hydrolase from previously purified epoxide hydrolases.     

Specificity and inhibition studies of human renal dipeptidase

Purified human renal dipeptidase was shown to exhibit no detectable activity against substrates that are characteristic for other known mammalian peptidases. The enzymic activities that were assayed were: aminopeptidase A, aminopeptidase B, aminopeptidase M, aminopeptidase P, and tripeptidase. A quantitative assay for renal dipeptidase was developed which measures the rate of release of glycine from glycylpeptides by pre-column derivatization of the amino acid with phenylisothiocyanate followed by high-performance liquid chromatography. The ratio of Vmax/Km for a series of dipeptides was used as an index of the enzyme's preference for substrates. According to the data obtained, the enzyme prefers that a bulky, hydrophobic group of the dipeptide be located at the N-terminal position. This suggests that the substrate-binding site of the enzyme may provide a hydrophobic pocket to accommodate the hydrophobic moiety at the N-terminus of the dipeptide. The unsaturated dipeptide substrate, glycyldehydrophenylalanine, was employed in spectrophotometric assays to provide kinetic analyses of enzymic inhibition. The inhibitory effect of dithiothreitol was immediate, and the kinetic data indicated reversible, competitive inhibition. These results suggest that the inhibitor competes with substrate for a coordination site of zinc within the active site of the enzyme. The reaction of renal dipeptidase with the transition-state peptide analog, bestatin, was time dependent, and velocity measurements were made after the inhibitor had been incubated with the enzyme until constant rates were observed. These steady-state rate measurements, made following preincubation of enzyme with inhibitor, were employed to show that bestatin caused apparent non-competitive inhibition of the enzyme. The inhibitory effect of the beta-lactam inhibitor, cilastatin, upon the oligomeric dipeptidase was shown to be competitive. Graphical analysis of this inhibition indicated that the subunits of the enzyme react independently during enzymic catalysis and that the catalytic event is not influenced by cooperativity between sites on the subunits. The conversion of leukotriene D4 to leukotriene E4 in the presence of human renal dipeptidase was demonstrated by HPLC procedures. This bioconversion reaction was quantitated by derivatizing the glycine produced by cleavage of the cysteinylglycine bond and isolating this derivative as a function of time. The relationship between the purified enzyme concentration and enzyme activity against leukotriene D4 was shown to be linear over the enzyme concentration range of 1 ng through 69 ng in this assay.(ABSTRACT TRUNCATED AT 400 WORDS)     

Human peritoneal macrophages synthesize leukotrienes B4 and C4

Macrophages were isolated from the dialysis fluid of patients undergoing continuous ambulatory peritoneal dialysis and separated by gradient centrifugation and purification on 50% Percoll. The cells were prelabeled with [14C]arachidonic acid for 1.5 h. The labeled cells were then incubated with calcium ionophore A23187 (1 microM), serum-treated zymosan (200 micrograms/ml), and a lipoxygenase inhibitor, nordihydroguairetic acid (1 X 10(-5) M). The arachidonate metabolites in the medium were separated on Sep-Pak columns, and finally purified by reverse-phase high-pressure liquid chromatography (HPLC). The labeled products co-chromatographed with authentic leukotriene B4 and leukotriene C4 standards. Serum-treated zymosan and A23187 significantly stimulated and nordihydroguairetic acid significantly inhibited leukotriene synthesis. Leukotriene D4 was not detected, which suggests that these cells contain low gamma-glutamyltranspeptidase or high dipeptidase activity. These results establish, for the first time, that human peritoneal macrophages synthesize the lipoxygenase products, leukotriene B4 and leukotriene C4.     

Cilastatin-sensitive dehydropeptidase I enzymes from three sources all catalyze carbapenem hydrolysis and conversion of leukotriene D4 to leukotriene E4

The dipeptidase, dehydropeptidase I (EC 3.4.13.11), was purified to homogeneity from rat lung, rat kidney, and hog kidney. Analysis of physical parameters (subunit molecular weights, Km values for glycyldehydrophenylalanine, Ki values for dehydropeptidase I inhibitors, and immunoreactivity) showed the rat dipeptidases to be similar to each other but different from the hog dipeptidase. However, all three enzymes hydrolyzed imipenem and converted leukotriene D4 to leukotriene E4, and these activities were inhibited by cilastatin.     

The purification and characterization of a proline dipeptidase from guinea pig brain

A proline dipeptidase (EC 3.4.13.9) from guinea pig brain was purified to over 90% homogeneity by a combination of ammonium sulfate fractionation, DEAE-cellulose chromatography, calcium phosphate-cellulose chromatography, chromatofocusing, and gel filtration on Sephadex G-200. A purification factor of 2718-fold was obtained with a yield of 7%. The purified enzyme was found to have an apparent molecular weight of 132,000 and to consist of two dissimilar subunits of molecular weights 64,000 and 68,000. The substrate specificity of the enzyme is not that of a strict proline dipeptidase. Although it preferentially hydrolyzes proline dipeptides (Leu-Pro) it also hydrolyzes prolyl dipeptides (Pro-Leu) and dipeptides not containing proline (Leu-Leu). The purified enzyme preparation exhibited weak aminoacylproline aminopeptidase activity against Arg-Pro-Pro but it did not exhibit any post-proline dipeptidyl aminopeptidase, post-proline cleaving endopeptidase, proline iminopeptidase, prolyl carboxypeptidase or carboxypeptidase P activities when tested with a large variety of peptides and arylamides. With all of the proline and prolyl dipeptides examined the enzyme exhibited biphasic kinetics (two distinct slopes on Lineweaver-Burk plots). However, with Leu-Leu as substrate normal Michaelis-Menten kinetics were obeyed.     

Rat brain N-acetylated alpha-linked acidic dipeptidase activity. Purification and immunologic characterization

N-Acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase) is a membrane-bound metallopeptidase that cleaves glutamate from the endogenous neuropeptide N-acetyl-L-aspartyl-L-glutamate. In this report, we have solubilized NAALA dipeptidase activity from synaptosomal membranes with Triton X-100 and purified it to apparent homogeneity by sequential column chromatography on DEAE-Sepharose, CM-Sepharose, and lentil lectin-Sepharose. This procedure resulted in a 720-fold purification with 1.6% yield. The purified ezyme migrated as a single silver-stained band on a sodium dodecyl sulfate gel with an apparent molecular weight of 94 kDa. Using an enzymatic stain to visualize NAALA dipeptidase activity within a gel matrix, we have confirmed that the 94-kDa band is, indeed, NAALA dipeptidase. The purified enzyme was characterized and found to be pharmacologically similar to NAALA dipeptidase activity described previously in synaptosomal membrane extracts. Using the purified NAALA dipeptidase as antigen, we have raised specific and high titer polyclonal antibodies in guinea pig. Immunocytochemical studies show intense NAALA dipeptidase immunoreactivity in the cerebellar and renal cortices.     

Purification and Characterization of a Dipeptidase from Lactobacillus helveticus SBT 2171

A metal-dependent dipeptidase was purified to homogeneity from a cell extract of Lactobacillus helveticus SBT 2171 by fast protein liquid chromatography. The enzyme was purified 237-fold from the extract, with a yield of 1.8%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band with a molecular weight of 50,000. The dipeptidase hydrolyzes a range of only dipeptides. Dipeptides containing proline, glutamic acid, and aspartic acid are not hydrolyzed. The enzyme was shown to be a metalloenzyme with a pH optimum of 8.0 and a temperature optimum of 55(deg)C. Dithiol-reducing reagents exert strong inhibition on enzyme activity. Kinetic studies indicated that the enzyme has a relative average affinity for leucyl-leucine (K(infm), 0.5 mM). The negative immunoresponse of the purified enzyme with monoclonal antibodies raised against a dipeptidase from Lactococcus lactis subsp. cremoris Wg2 shows that both enzymes can be immunologically distinguished.     

Leukotriene synthesis by human gastrointestinal tissues

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassay for prostaglandin E2, leukotriene B4 and sulfidopeptide leukotrienes. The leukotriene immunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37 degrees C, fragments of human gastric, jejuno-ileal and colonic mucosa released considerably larger amounts of prostaglandin E2 than of leukotriene B4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B4, sulfidopeptide leukotrienes and prostaglandin E2 than normal colonic mucosa. Ionophore A23187 (5 micrograms/ml) did not stimulate release of prostaglandin E2 from any of the tissues investigated, but enhanced release of leukotriene B4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B4 co-chromatographed almost exclusively with standard leukotriene B4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C4, D4 and E4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D4 and E4, while release of leukotriene C4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [3H]leukotriene D4 and [3H]leukotriene E4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes gamma-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.     

Ectoenzymes of the kidney microvillar membrane. Isolation and characterization of the amphipathic form of renal dipeptidase and hydrolysis of its glycosyl-phosphatidylinositol anchor by an activity in plasma.

Renal dipeptidase (EC 3.4.13.11) has been solubilized from pig kidney microvillar membranes with n-octyl-beta-D-glucopyranoside and then purified by affinity chromatography on cilastatin-Sepharose. The enzyme exists as a disulphide-linked dimer of two identical subunits of Mr 45,000 each. The purified dipeptidase partitioned into the detergent-rich phase upon phase separation in Triton X-114 and reconstituted into liposomes consistent with the presence of the glycosyl-phosphatidylinositol membrane anchor. The N-terminal amino acid sequence of the amphipathic, detergent-solubilized, form of renal dipeptidase was identical with that of the hydrophilic, phospholipase-solubilized, form, locating the membrane anchor at the C-terminus of the protein. The glycosyl-phosphatidylinositol anchor of both purified and microvillar membrane renal dipeptidase was a substrate for an activity in pig plasma which displayed properties similar to those of a previously described phospholipase D. The cross-reacting determinant of the glycosyl-phosphatidylinositol anchor was generated by incubation of purified renal dipeptidase with bacterial phosphatidylinositol-specific phospholipase c, whereas the anchor-degrading activity in plasma failed to generate this determinant.     

Glutathione-degrading enzymes of microvillus membranes

Microvillus membranes from rat kidney, jejunum, and epididymis have been purified by the Ca precipitation method. The membranes exhibit enrichment in specific activities of gamma-glutamyl transpeptidase, aminopeptidase M, and a dipeptidase. The latter has been characterized and shown to be the principal activity responsible for the hydrolysis of S derivatives of Cys-Gly (including cystinyl-bis-glycine (Cys-bis-Gly) and 5-hydroxy-6-S-cysteinylglycyl-1-7,9-trans-11,14-cis-eicosatetraenoic acid (leukotriene D4)). A method is described for the simultaneous purification of papain-solubilized forms of the three enzymes from renal microvilli. Dipeptidase (Mr = 105,000) appears to be a zinc metalloprotein composed of two Mr = 50,000 subunits. The enzyme is severalfold more effective in the hydrolysis of dipeptides than aminopeptidase M. Dipeptidase, in contrast to aminopeptidase M, is inhibited by thiol compounds; Cys-Gly, in particular, is a potent inhibitor (Ki = 20 microM). The inhibition of dipeptidase by thiols has been employed to probe the relative significance of dipeptidase and aminopeptidase M in the metabolism of glutathione and its derivatives at the membrane surface.     

Characterization of dehydropeptidase I in the rat lung

The activity of dehydropeptidase I in rat tissues decreases in the order of lung greater than kidney greater than liver-spleen greater than other tissues, while aminopeptidase activity is high in the kidney, and lower in the lung than in other tissues. Dehydropeptidase I was solubilized from the membrane fraction of rat lung by treatment with papain and purified by DEAE-cellulose column chromatography, affinity chromatography on concanavalin-A-Sepharose and high-performance liquid chromatography gel filtration. The purified preparation was found to be homogeneous on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The relative molecular mass was estimated to be 150,000 by gel filtration, comprising a homodimer of two 80,000-Mr subunits. The enzyme activity was inhibited by cilastatin, o-phenanthroline and ATP. This enzyme catalyzed the hydrolysis of S(substituent)-L-cysteinyl-glycine adducts such as L-cystinyl-bis(glycine) and N-ethylmaleimide-S-L-cysteinyl-glycine, as well as the conversion of leukotriene D4 to E4. Furthermore it catalyzed a hydrolytic splitting of L-Leu-L-Leu, but not S-benzyl-L-cysteine p-nitroanilide, which is a good substrate for aminopeptidase. Our enzyme preparation was immunologically identical to the rat renal dehydropeptidase I. The physiological significance of the pulmonary dehydropeptidase I on the metabolism of glutathione and its adducts is discussed.     

Metabolism of arachidonic acid by guinea pig Clara cells.

A method for the isolation of non-ciliated bronchiolar epithelial (Clara) cells from the guinea pig is described. Following digestion of the lung tissue with Type XXIV protease, the isolated lung cells showed a viability greater than 90% and contained 3% of Clara cells. Several cell populations were then separated on the basis of size using 2 centrifugal elutriations. The macrophages and endothelial cells were removed from the Clara cells enriched fractions by differential adherence on Petri dishes. The Clara cell-rich suspension was then further purified by centrifugation on Percoll non-continuous density gradients consisting of 48-52-55% Percoll solution. The lower interface and the pellet of the non-continuous gradient consisted of approximately 80% Clara cells. Identification of isolated Clara cells was confirmed by light microscopic observations after nitroblue tetrazolium staining and by ultrastructural characteristic features as observed by electron microscopy. The metabolism of arachidonic acid into prostaglandins and TxB2 by purified Clara cells was examined by enzyme immunoassay (EIA) and leukotriene formation was investigated by reverse phase high performance liquid chromatography (RP-HPLC). Enriched guinea pig Clara cells incubated with arachidonic acid released TxB2, PGE2 and 6-keto PGF1 alpha, but did not produce leukotrienes. These cells could however transform exogenous leukotriene A4 into leukotriene B4. These results suggest that guinea pig Clara cells possess the enzymes of the cyclooxygenase pathway required for TxB2, PGE2 and 6-keto-PGF1 alpha synthesis. Clara cells do not possess the 5-lipoxygenase enzyme but show some leukotriene A4 hydrolase activity since they can produce leukotriene B4 upon incubation with leukotriene A4.     

Hydrolysis of the brain dipeptide N-acetyl-L-aspartyl-L-glutamate. Identification and characterization of a novel N-acetylated alpha-linked acidic dipeptidase activity from rat brain

High performance liquid chromatography studies documented the presence of an enzyme activity, N-acetylated alpha-linked acidic dipeptidase (NAALA dipeptidase), in rat brain membranes that cleaves the endogenous brain dipeptide, N-acetyl-L-aspartyl-L-glutamate to N-acetyl-aspartate and glutamate. With ion exchange chromatography, which quantitatively separated [3,4-3H]glutamate from N-acetyl-L-aspartyl-L-[3,4-3H]glutamate, we found that NAALA dipeptidase activity was essentially restricted to nervous tissue and kidney. We characterized NAALA dipeptidase activity in lysed synaptosomal membranes obtained from rat forebrain. Membrane-bound NAALA dipeptidase activity was optimal between pH 6.0 and 7.4 at 37 degrees C. Eadie-Hofstee analysis of kinetic data revealed a rather high apparent affinity for N-acetyl-L-aspartyl-L-glutamate with a Km = 540 nM and a Vmax = 180 nM/mg of protein/min. While NAALA dipeptidase showed a requirement for monovalent anions such as Cl-, the polyvalent anions phosphate and sulfate inhibited enzyme activity 50% at 100 microM and 1 mM, respectively. The divalent metal ion chelators EGTA, EDTA, and o-phenanthroline completely abolished activity, which was partially restored by manganese. Treatment of membranes with 1 mM dithiothreitol abolished NAALA dipeptidase activity. NAALA dipeptidase activity was also sensitive to the aminopeptidase inhibitors bestatin and puromycin, although not to the selective aminopeptidase A inhibitor amastatin. Structure-activity relationships inferred from inhibitor studies suggest that this enzyme shows specificity for N-acetylated alpha-linked acidic dipeptides. NAALA dipeptidase was also potently inhibited by the excitatory amino acid agonist L-quisqualate. Comparison of the properties of NAALA dipeptidase to those of previously characterized enzymes suggests that this is a novel peptidase which may be involved in the synaptic degradation of N-acetyl-L-aspartyl-L-glutamate.     

The proteolytic system of Lactobacillus sanfrancisco CB1: purification and characterization of a proteinase, a dipeptidase, and an aminopeptidase.

A cell envelope 57-kDa proteinase, a cytoplasmic 65-kDa dipeptidase, and a 75-kDa aminopeptidase were purified from Lactobacillus sanfrancisco CB1 sourdough lactic acid bacterium by sequential fast protein liquid chromatography steps. All of the enzymes are monomers. The proteinase was most active at pH 7.0 and 40 degrees C, while aminopeptidase and dipeptidase had optima at pH 7.5 and 30 to 35 degrees C. Relatively high activities were observed at the pH and temperature of the sourdough fermentation. The proteinase is a serine enzyme. Urea-polyacrylamide gel electrophoresis of digest of alpha s1- and beta-caseins showed differences in the pattern of peptides released by the purified proteinase and those produced by crude preparations of the cell envelope proteinases of Lactobacillus delbrueckii subsp. bulgaricus B397 and Lactococcus lactis subsp. lactis SK11. Reversed-phase fast protein liquid chromatography of gliadin digests showed a more-complex peptide pattern produced by the proteinase of Lactobacillus sanfrancisco CB1. The dipeptidase is a metalloenzyme with high affinity for dipeptides containing hydrophobic amino acids but had no activity on tripeptides or larger peptides. The aminopeptidase was also inhibited by metal-chelating agents, and showed a broad N-terminal hydrolytic activity including di- and tripeptides. Km values of 0.70 and 0.44 mM were determined for the dipeptidase on Leu-Leu and the aminopeptidase on Leu-p-nitroanilide, respectively.     

Salmonella typhimurium peptidase active on carnosine.

Wild-type Salmonella typhimurium can use carnosine (beta-alanyl-L-histidine) as a source of histidine, but carnosine utilization is blocked in particular mutants defective in the constitutive enzyme peptidase D, the product of the pepD gene. Biochemical evidence for assigning carnosinase activity to peptidase D (a broad-specificity dipeptidase) includes: (i) coelution of carnosinase and dipeptidase activity from diethylaminoethyl-cellulose and Bio-Gel P-300 columns; (ii) coelectrophoresis of carnosinase and dipeptidase on polyacrylamide gels; and (iii) inactivation of carnosinase and dipeptidase activities at identical rates at both 4 and 42 degrees C. Genetic evidence indicates that mutations leading to loss of carnosinase activity map at pepD. Several independent pepD mutants have been isolated by different selection procedures, and the patterns of peptide utilization of strains carrying various pepD alleles have been studied. Many pepD mutations lead to the production of partially active peptidase D enzymes with substrate specificities that differ strikingly from those of the wild-type enzyme. The growth yields of carnosinase-deficient strains growing in Difco nutrient broth indicate that carnosine is the major utilizable source of histidine in this medium.     

Leukotriene A4 hydrolase: an anion activated peptidase.

The peptidase activity of leukotriene A4 hydrolase purified from human leukocytes has been characterized, utilizing synthetic amides as substrates. The enzyme was stimulated by several monovalent anions. Thiocyanate ions were most effective followed by chloride and bromide ions. In phosphate buffer alone the peptidase activity towards alanine-4-nitroanilide was barely detectable and addition of 100 mM NaCl increased the specific activity more than 20-fold. Increasing the concentration of NaCl (or NaSCN) did not significantly affect the apparent Km for the substrate alanine-4-nitroanilide, but resulted in a dose dependent increase of Vmax. The stimulatory effect of these anions on the reaction velocities appeared to obey saturation kinetics and thus indicated the presence of an anion binding site. Apparent affinity constants for chloride and thiocyanate ions were calculated to 100 and 50 mM, respectively. In contrast to the effect on the peptidase activity, no chloride-stimulation could be detected of the epoxide hydrolase activity of this enzyme, i.e., the conversion of leukotriene A4 into leukotriene B4. In conclusion, the results indicate that under physiological conditions, chloride ions may selectively stimulate the peptidase activity of LTA4 hydrolase. Also, the differences in chloride concentrations between cellular compartments suggest that a possible proteolytic function of the enzyme may be limited to the extracellular space.     

Cilastatin (MK 0791) is a potent and specific inhibitor of the renal leukotriene D4-dipeptidase

The metabolism of leukotriene D4 to leukotriene E4 by a dipeptidase of kidney tissue is strongly inhibited by cilastatin (MK 0791) a known renal dehydropeptidase-I inhibitor. The comparison with similar enzyme activities from other tissues (liver, lung, serum, polymorphonuclear granulocytes) revealed a high specificity of cilastatin for the kidney enzyme which was found to be associated with the microsomal fraction. The lowest detectable inhibitory concentration of cilastatin within renal tissue was 8 X 10(-8)M.     

Purification and partial characterization of a tripeptidase from Pediococcus pentosaceus K9.2.

A tripeptidase was purified from the cytoplasm of Pediococcus pentosaceus K9.2 by anion-exchange chromatography, gel filtration chromatography, and high-performance liquid chromatography. The molecular mass of the enzyme was estimated by gel filtration at 100,000 Da. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified peptidase showed one protein band of 45,000 Da. Optimal enzyme activity was obtained at pH 7.0 and at 50 degrees C. The peptidase hydrolyzed all tripeptides tested. Cleavage was not observed with dipeptides, oligopeptides, or amino acid-p-nitroanilide derivatives. Strong inhibition of activity was caused by EDTA, 1,10-phenanthroline, dithiothreitol, and beta-mercaptoethanol, whereas phenylmethylsulfonyl fluoride and sulfur-reactive reagents had no effect on peptidase activity. Mg2+, Mn2+, and Ca2+ stimulated the hydrolyzing activity of the enzyme. The 20 N-terminal amino acids of the tripeptidase from P. pentosaceus had 84% identity with those from the corresponding N-terminal region of the tripeptidase from Lactococcus lactis subsp. cremoris Wg2.