A simple spectrophotometric assay for amino acyl arylamidases (naphthylamidases, aminopeptidases)

Beneficial influence of dietary spices on the ultrastructure and fluidity of the intestinal brush border in rats

The beneficial influence of three common spices was examined in experimental rats on: (i) the membrane fluidity of intestinal brush-border membranes (BBM), (ii) the activity of intestinal membrane-bound enzymes, and (iii) ultrastructural alterations in the intestinal epithelium. Groups of male Wistar rats were maintained on dietary black pepper (0.5 %), red pepper (3.0 %), ginger (0.05 %) and spice bioactive compounds piperine (0.02 %) and capsaicin (0.01 %) for 8 weeks. A membrane fluidity study using an apolar fluorescent probe showed increased BBM fluidity in all the spice-fed animals. This was corroborated by a decreased cholesterol:phospholipid ratio in the jejunal and ileal regions of the intestine. These dietary spices stimulated the activities of BBM enzymes (glycyl-glycine dipeptidase, leucine amino peptidase and gamma-glutamyl transpeptidase) in the jejunal mucosa, suggesting a modulation in membrane dynamics due to the apolar spice bioactive compounds interacting with surrounding lipids and hydrophobic portions in the protein vicinity, which may decrease the tendency of membrane lipids to act as steric constraints to enzyme proteins and thus modify enzyme conformation. Scanning electronic microscopy of the intestinal villi in these spice treatments revealed alterations in the ultrastructure, especially an increase in microvilli length and perimeter which would mean a beneficial increase in the absorptive surface of the small intestine, providing for an increased bioavailability of micronutrients. Thus, dietary spices (black pepper, red pepper and ginger) were evidenced to induce alterations in BBM fluidity and passive permeability property, associated with the induction of an increased microvilli length and perimeter, resulting in an increased absorptive surface of the small intestine.

Significance of the conserved Tyr352 and Asp380 residues in the catalytic activity of Bacillus stearothermophilus aminopeptidase II as evaluated by site-directed mutagenesis

The importance of the conserved Tyr352 and Asp380 residues of Bacillus stearothermophilus aminopeptidase II (AP-II) was investigated by site-directed mutagenesis. The wild-type and mutant enzymes were expressed in recombinant Escherichia coli M15 cells and the 45-kD proteins were purified from the cell-free extracts by Ni(2+)-NTA resin. The specific activity for Tyr352 and Asp380 replacements was decreased by more than 3.5-fold. Detailed analysis of the kinetic consequences in the mutant proteins revealed that the K (m) values were increased 1.9- to 2.6-fold with respect to wild-type enzyme. Catalytic efficiencies (k (cat)/K (m)) of mutant proteins were between 3.5- and 31-fold lower than the corresponding value of the wild-type enzyme. Tryptophan emission fluorescence and circular dichroism spectra were nearly identical for wild-type and mutant enzymes. These results indicate that residues Tyr352 and Asp380 are essential for the proper function of AP-II.

Piperine modulates permeability characteristics of intestine by inducing alterations in membrane dynamics: influence on brush border membrane fluidity, ultrastructure and enzyme kinetics

Piperine (1-Piperoyl piperidine) is a major alkaloid of Piper nigrum Linn. and Piper longum Linn. It is shown to possess bioavailability-enhancing activity with various structurally and therapeutically diverse drugs. The mechanism of enhancing the bioavailability, is, however, not understood. We hypothesize that piperine's bioavailability-enhancing property may be attributed to increased absorption, which may be due to alteration in membrane lipid dynamics and change in the conformation of enzymes in the intestine. Results of membrane fluidity studies using an apolar fluorescent probe, pyrene (which measures the fluid properties of hydrocarbon core), showed an increase in intestinal brush border membrane (BBM) fluidity. Piperine also stimulated Leucine amino peptidase and Glycyl-glycine dipeptidase activity, due to the alteration in enzyme kinetics. This suggests that piperine could modulate the membrane dynamics due to its apolar nature by interacting with surrounding lipids and hydrophobic portions in the protein vicinity, which may decrease the tendency of membrane lipids to act as stearic constrains to enzyme proteins and thus modify enzyme conformation. Ultra structural studies with piperine showed an increase in microvilli length with a prominent increase in free ribosomes and ribosomes on the endoplasmic reticulum in enterocytes, suggesting that synthesis or turnover of cytoskeletal components or membrane proteins may be involved in the observed effect. In conclusion, it is suggested that piperine may be inducing alterations in membrane dynamics and permeation characteristics, along with induction in the synthesis of proteins associated with cytoskeletal function, resulting in an increase in the small intestine absorptive surface, thus assisting efficient permeation through the epithelial barrier.

One step purification and characterization of the pyrrolidone carboxyl peptidase ofStreptococcus pyogenesover-expressed inEscherichia coli

Pyrrolidone carboxyl peptidase (EC 3.4.11.8) (Pcp), an enzyme which selectively removes pyrrolidone carboxylic acid (PCA) from some PCA-peptides and -proteins, was demonstrated in bacteria and in plant, animal and human tissues. In this paper we describe the purification to homogeneity of the enzyme of Streptococcus pyogenes, over-expressed in Escherichia coli. This was achieved, for the first time in one step, by hydrophobic interaction chromatography. Analysis under non-denaturing conditions revealed a molecular mass of 85 kDa and in the presence of sodium dodecyl sulfate gave a molecular mass of 23.5 kDa. Investigations on enzymatic properties showed that the Pcp over-expressed in E. coli disclosed properties similar to those found for the enzyme extracted from S. pyogenes or for some other Pcps studied previously. Thus the over-expressed enzyme should serve as a suitable source for N-terminal unblocking prior to some PCA protein sequencing.

High pressure processing of fresh seafoods

Crude proteolytic enzyme extracts were prepared from the muscle tissues of two fish species, bluefish and sheephead, and subjected to high hydrostatic pressure treatments (from 1,000-3,000 atm), and monitored for residual activity for cathepsin C, collagenase, chymotrypsin-like and trypsin-like enzymes versus homologous enzymes from bovine. The fish enzymes were more sensitive to hydrostatic pressure than the mammalian enzymes. The extent of enzyme inactivation achieved depended on both the amount of pressure applied, the duration of pressurization, and on the source material. Pressure treatment of fresh fish flesh formed products whose color deteriorated (cooked appearance) with increasing pressure as well as holding time. Application of pressure also improved tissue firmness or strength of fresh fish up to 2,000 atm and a holding time of 10 min, beyond which texture generally deteriorated. The combined use of pressure in combination with the broad spectrum protease inhibitor, alpha 2-macroglobulin, enhanced the capacity of the hydrostatic pressure technology to achieve a more lasting inactivation of endogenous enzymes to form stable fish gels.

Oral insulinlike growth factor-I stimulates intestinal enzyme maturation in newborn rats

Insulinlike growth factor-I (IGF-I) has been found in the milk of various species. To investigate if milk-borne IGF-I has any effect on postnatal gut development in neonatal animals, newborn rat pups were given orally 1 microg recombinant human IGF-I daily for 3 days. For comparison, a separate group of newborn pups was given 150 microg hydrocortisone, the hormone known to stimulate intestinal maturation in neonatal rats. Oral IGF-I treatment had no significant effect on the animal body weight nor on the weight of the stomach, small and large intestines, and pancreas. Oral administration of hydrocortisone significantly reduced body weight gain, but it had no apparent effect on internal organ weights. Both IGF-I and hydrocortisone treatments, however, significantly increased lactase, maltase and sucrase activities and hydrocortisone significantly increased aminopeptidase activity at the proximal small intestine when compared with the control. The finding supports the hypothesis that milk-borne IGF-I may play a role in regulating postnatal gut development in the suckling young.

Mutational analysis of the active site of Pseudomonas fluorescens pyrrolidone carboxyl peptidase

On the basis of chemical inhibition studies and a multiple alignment of four pyrrolidone carboxyl peptidase (Pcp) amino acid sequences, seven conserved residues of the Pseudomonas fluorescens Pcp, which might be important for enzyme activity, have been modified by site-directed mutagenesis experiments. Wild-type and mutant Pcps were expressed in Escherichia coli, purified, and characterized by the ability to cleave the synthetic chromogenic substrate pyroglutamyl-beta-naphthylamide and the dipeptide pyroglutamyl-alanine. Substitution of Glu-10 and Glu-22 by Gln led to enzymes which displayed catalytic properties and sensitivities to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide similar to those of the wild-type Pcp. These residues are not essential for the catalytic activity. Replacement of Asp-89 by Asn and Ala resulted in enzymes which retained nearly 25% of activity and which had no activity, respectively. Substitution of the Cys-144 and His-166 residues by Ala and Ser, respectively, resulted in inactive enzymes. Proteins with changes of Glu-81 to Gln and Asp-94 to Asn were not detectable in crude extract and were probably unstable in bacteria. Our results are consistent with the proposal that Cys-144 and His-166 constitute the nucleophilic and imidazole residues of the Pcp active site, while residue Glu-81, Asp-89, or Asp-94 might constitute the third part of the active site. These results lead us to propose Pcps as a new class of thiol aminopeptidases.

Isolation and characterization of pcp, a gene encoding a pyrrolidone carboxyl peptidase in Staphylococcus aureus

The pcp gene, encoding a pyrrolidone carboxyl peptidase (PYRase), was cloned from a lambda GT11 genomic library prepared from Staphylococcus aureus FDA 574 and sequenced. The pcp gene is located 740 bp downstream from cna, a gene that encodes a collagen-binding adhesin in S. aureus. S. aureus pcp encodes a 212-amino-acid (aa) polypeptide. The pcp gene was overexpressed in Escherichia coli and the PYRase purified to homogeneity. The recombinant enzyme exhibited biological activity, as determined using the chromogenic substrate L-pyroglutamyl-beta-napthylamide. Biochemical analysis of the PYRase using thiol-blocking chemicals suggested that the enzyme belongs to the cysteine peptidase family. Moreover, multiple sequence alignment revealed a high degree of similarity to previously described bacterial PYRases. This family of peptidases has been used to selectively remove the N-terminal pyrrolidone carboxylic acid residue found on certain blocked proteins and peptides prior to aa sequencing. However, the exact biological role of PYRases has yet to be elucidated.

Degradation of angiotensin I to [des-Asp1]angiotensin I by a novel aminopeptidase in the rat hypothalamus

The particulate enzyme that degrades angiotensin I (ANG I) to [des-aspartate1]angiotensin I ([des-Asp1]ANG I) in the hypothalamic homogenate of the rat has been established as a specific aminopeptidase. The major characteristics is its resistance to inhibition by 10(-4) M amastatin, bestatin and EDTA. Among the four amino acyl-beta-naphthylamides (aspartyl, glutamyl-, arginyl- and leucyl-beta-naphthylamide), aspartyl-beta-naphthylamide is the most susceptible substrate of the enzyme; being degraded at twice the rate of arginyl-, and leucyl-beta-naphthylamide, and six times that of glutamyl-beta-naphthylamide. Although the precise role of this aminopeptidase has yet to be determined, its presence establishes the existence of a specific pathway for the degradation of ANG I that bypasses the formation of ANG II. The relationship between degradation and hypertension is shown by our recent findings that the formation of [des-Asp1]ANG I form ANG I in the hypothalamic homogenate of the spontaneously hypertensive rat (SHR) is significantly enhanced, and the findings of other investigators that the production of ANG II by neuronal cultures of the SHR is significantly decreased.

Characterization of the pcp gene of Pseudomonas fluorescens and of its product, pyrrolidone carboxyl peptidase (Pcp)

The gene pcp, encoding pyrrolidone carboxyl peptidase (Pcp), from Pseudomonas fluorescens MFO was cloned and its nucleotide sequence was determined. This sequence contains a unique open reading frame (pcp) coding for a polypeptide of 213 amino acids (M(r) 22,441) which has significant homology to the Pcps from Streptococcus pyogenes, Bacillus subtilis, and Bacillus amyloliquefaciens. Comparison of the four Pcp sequences revealed two highly conserved motifs which may be involved in the active site of these enzymes. The cloned Pcp from P. fluorescens was purified to homogeneity and appears to exist as a dimer. This enzyme displays a Michaelis constant of 0.21 mM with L-pyroglutamyl-beta-naphthylamide as the substrate and an absolute substrate specificity towards N-terminal pyroglutamyl residues. Studies of inhibition by chemical compounds revealed that the cysteine and histidine residues are essential for enzyme activity. From their conservation in the four enzyme sequences, the Cys-144 and His-166 amino acids are proposed to form a part of the active site of these enzymes.

Purification and characterization of recombinant pyrrolidone carboxyl peptidase of Bacillus subtilis

Bacillus subtilis pyrrolidone carboxyl peptidase (Pcp) overexpressed in Escherichia coli was purified to homogeneity in less than 12 h using ammonium sulphate precipitation and hydrophobic interaction chromatography. The enzyme, which removes amino-terminal L-pyroglutamic acid from peptides, appears to be a tetramer of 25,200 molecular mass subunits. The protein cross-reacted with polyclonal antibodies raised against Pcp from Streptococcus pyogenes. The overexpressed enzyme exhibits an absolute substrate specificity towards N-terminal pyroglutamyl residues with a Michaelis constant of 1.04 mM for L-pyroglutamyl-beta-naphthylamide. The enzyme could be used for the removal of pyroglutamyl residues that block amino termini of proteins and peptides before performing Edman sequential degradation.

Cloning and nucleotide sequence of opdA, the gene encoding oligopeptidase A in Salmonella typhimurium

The opdA gene (formerly called optA) of Salmonella typhimurium encodes a metallopeptidase, oligopeptidase A (OpdA), first recognized by its ability to cleave and allow utilization of N-acetyl-L-Ala4 (E. R. Vimr, L. Green, and C. G. Miller, J. Bacteriol. 153:1259-1265, 1983). Derivatives of pBR328 carrying the opdA gene were isolated and shown to express oligopeptidase activity at levels approximately 100-fold higher than that of the wild type. These plasmids complemented all of the phenotypes associated with opdA mutations (failure to use N-acetyl-L-Ala4, defective phage P22 development, and diminished endopeptidase activity). The opdA region of one of these plasmids (pCM127) was defined by insertions of Tn1000 (gamma delta), and these insertions were used as priming sites to determine the nucleotide sequence of a 2,843-bp segment of the insert DNA. This region contained an open reading frame coding for a 680-amino-acid protein, the N terminus of which agreed with that determined for purified OpdA. This open reading frame contained both a sequence motif typical of Zn2+ metalloproteases and a putative sigma 32 promoter. However, no induction was detected upon temperature shift by using a beta-galactosidase operon fusion. The predicted OpdA sequence showed similarity to dipeptidyl carboxypeptidase, the product of the S. typhimurium gene dcp, and to rat metallopeptidase EC 3.4.24.15., which is involved in peptide hormone processing.

Purification and characterization of proteinase yscJ, a new yeast peptidase

A newly recognized peptidase, designated proteinase yscJ, was purified from the yeast Saccharomyces cerevisiae. The enzyme is of non-vacuolar origin and cleaves the Tyr-Lys bond of the synthetic peptide substrate Cbz-Tyr-Lys-Arg-NH-Ph (Cbz, benzyloxycarbonyl; NH-Ph, 4-nitroanilide) and the Glu-Lys bond of the substrate Boc-Glu-Lys-Lys-NH-Mec (Boc, butoxycarbonyl; Mec, 4-methylcoumarinyl) with high efficiency. Optimum pH for cleavage of Cbz-Tyr-Lys-Arg-NH-Ph is in the range 7.0-7.5. The purified enzyme has a molecular mass of approximately 58 kDa, as judged by gel filtration on a Superose 12 FPLC column. Mercury compounds and EDTA were found to be potent inhibitors of proteinase yscJ activity.

Isolation and properties of a metalloproteinase from buckwheat (Fagopyrum esculentum) seeds

A homogeneous preparation of metalloproteinase, purified 1000-fold, was obtained from buckwheat (Fagopyrum esculentum) seeds. The Mr of the enzyme, determined by SDS/PAGE, was 34,000 (it was 39,000 by gel chromatography). Its pH optimum was 8.0-8.2 with 13 S globulin, from buckwheat seeds, as substrate. Atomic-absorption spectroscopy revealed the presence of one Zn2+ ion per enzyme molecule. The enzyme was completely inhibited by EDTA (1 mM), zincone (1 mM) and 1, 10-phenanthroline (1 mM). The metalloproteinase performed limited proteolysis of the following seed storage proteins: 13 S globulin from buckwheat seeds and 11 S globulin from soybean (Glycine max) seeds. It hydrolysed three peptide bonds formed by the amino groups of Leu15, Tyr16 and Phe25 in the oxidized B-chain of insulin. In its main properties the enzyme is similar to metalloproteinases of animal and bacterial origin.

Aspartic proteinase from wheat seeds: isolation, properties and action on gliadin

Wheat endosperm was shown to contain an aspartic proteinase capable of hydrolyzing the wheat storage protein, gliadin, in vitro. The enzyme was purified to homogeneity by affinity chromatography on bacilliquin-silochrome, diethylaminoethyl-Toyopearl ion-exchange chromatography, chromatofocusing, and preparative polyacrylamide gel electrophoresis. The sedimentation constant of the enzyme was 3.4 S and the relative molecular mass (Mr), determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 58000 dalton (Da). The purified enzyme was completely inhibited by pepstain whereas other enzyme inhibitors did not affect its activity. The enzyme was found to hydrolyze mainly ω- and γ-gliadins with Mr's of 67000-95000 Da, with maximal activity at pH 4.5. The data make it possible to suggest that the enzyme has an endogenous function by initiating proteolysis of storage proteins in germinating wheat seeds.

Molecular and catalytic properties of a butyrylesterase from human red cells and brain

A butyrylesterase from human red cells was prepared to homogeneity using DEAE-cellulose, Ultrogel ACA-34, DEAE-Sephacel, and precipitation with 1.5 M (NH4)2SO4. The yield was 25-35% relative to the enzyme activity of the hemolysate. Because of its preference for butyric acid esters the enzyme was designated a butyrylesterase. With alpha-naphthyl butyrate the Km was 7.6 microM and the kcat, 48 s-1. The molecular weight was 340,000 and the subunit weight 85,000, indicating a tetrameric structure. The isoelectric pH was 4.0. The enzyme preparation did not contain cystine. Sialic acid or other carbohydrate components could not be detected. The enzyme was irreversibly inhibited by organophosphate esters and the second-order rate constant was 192 M-1 s-1 for diethyl p-nitrophenyl phosphate. For the brain enzyme the constant was 206 M-1 s-1. The enzyme was irreversibly inhibited by sulfhydryl reagents, indicating that the enzyme is a sulfhydryl-dependent serine esterase. The enzyme was identical to the butyrylesterase from human brain, and the two enzymes were immunochemically identical. An amino acid ester has been shown to be split at a higher rate than butyric acid esters; however, the specificity constant (kcat/Km) was lower for the amino acid ester than for the butyric acid ester. The enzyme did not exhibit amidase activity.

Purification and characterization of an aminopeptidase from bovine cornea

An aminopeptidase from bovine cornea has been extensively purified by gel filtration and ion-exchange chromatography. The purified enzyme with a molecular weight of 96,000 showed broad substrate specificity. All of the various aminoacyl bonds were hydrolyzed optimally at pH 6.5. The purified enzyme showed hydrolytic activity towards bioactive peptides such as enkephalins, bradykinin, and angiotensin-II. The enzyme was inhibited by bestatin, amastatin, puromycin, bacitracin, sulfhydryl reagents and metal chelators. Only Co2+ stimulated the enzyme whereas other heavy metal ions were toxic. The gross properties of the corneal enzyme resemble those of an aminopeptidase III isolated from bovine lens.

An improved spectrophotometric assay for leucine aminopeptidase

A sensitive assay to determine the activity of leucine aminopeptidase (EC 3.4.11.1), using L-leucine thiobenzyl ester as substrate, was developed. Hydrolysis of the ester by leucine aminopeptidase can be monitored in the presence of 5,5-dithiobis-(2-nitrobenzoic acid) by continuous spectrophotometric measurement at 412 nm. Comparison with some amide substrates showed that the thiol ester provides a much more sensitive assay, its specificity constant (Vmax./Km) being some 3000-fold higher than that of leucine p-nitroanilide.

Purification and characterization of ascamycin-hydrolysing aminopeptidase from Xanthomonas citri

A nucleoside antibiotic, ascamycin (9-beta-[5'-0-(N-L-alanyl) sulphamoyl-D-ribofuranosyl]-2-chloroadenine), has a selective antibacterial activity against Xanthomonas species. When ascamycin was dealanylated, dealanylascamycin showed a broad antibacterial activity against various Gram-negative and Gram-positive bacteria. Xanthomonas citri is susceptible to ascamycin by virtue of the ascamycin-dealanylating enzyme on the cell surface [Osada & Isono (1985) Antimicrob. Agents Chemother. 27, 230-233]. The enzyme (Xc aminopeptidase) was purified from X. citri cells by successive DEAE-cellulose, chromatofocusing and Sephadex G-100 column chromatography to a homogeneous state. The purified enzyme exhibited a single band with an Mr of 38 000 in SDS/polyacrylamide-gel electrophoresis. Gel filtration on a calibrated column indicated a similar Mr value. The isoelectric point of the enzyme was 5.7. The enzyme catalysed the hydrolysis of the alanyl group of ascamycin and liberated alanine from the sulphamoyl nucleoside. The enzyme also catalysed the hydrolysis of L-proline beta-naphthylamide and L-alanine beta-naphthylamide. The optimal pH and temperature for enzyme activity were pH 7.5-8.0 and 35-40 degrees C respectively. The enzyme was inhibited by thiol-enzyme inhibitors (i.e. rho-chloromercuribenzoate and N-ethylmaleimide), but was not affected by various naturally occurring aminopeptidase inhibitors (i.e. amastatin, bestatin, pepstatin and leupeptin). Mn2+ and Mg2+ activated the enzyme, whereas Cu2+, Zn2+ and Cd2+ were inhibitory.

Natural structural variation in enzymes as a tool in the study of mechanism exemplified by a comparison of the catalytic-site structure and characteristics of cathepsin B and papain. pH-dependent kinetics of the reactions of cathepsin B from bovine spleen and from rat liver with a thiol-specific two-protonic-state probe (2,2'-dipyridyl disulphide) and with a specific synthetic substrate (N-alpha-benzyloxycarbonyl-L-arginyl-L-arginine 2-naphthylamide)

Cathepsin B (EC 3.4.22.1) from bovine spleen and the analogous enzyme from rat liver were investigated at 25 degrees C at I0.1 in acidic media by kinetic study of (a) the reactions of their catalytic-site thiol groups towards the two-protonic-state reactivity probe 2,2'-dipyridyl disulphide and (b) their catalysis of the hydrolysis of N-alpha-benzyloxycarbonyl-L-arginyl-L-arginine 2-naphthylamide. Reactivity-probe kinetics showed that nucleophilic character is generated in the sulphur atom of cathepsin B by protonic dissociation with pKa 3.4, presumably to form an S-/ImH+ ion-pair. Substrate-catalysis kinetics showed that ion-pair formation is not sufficient to generate catalytic competence in cathepsin B, because catalytic activity is not generated as the pH is raised across pKa 3.4 but rather as it is raised across pKa 5-6 (5.1 for kcat; 5.6 for kcat./Km for the bovine spleen enzyme and 5.8 for kcat./Km for the rat liver enzyme). The implications of these results and of known structural differences between the catalytic sites of the rat liver enzyme and papain (EC 3.4.22.2) for the mechanism of cysteine-proteinase-catalysed hydrolysis are discussed.

Salmonella typhimurium mutations affecting utilization of L-leucine beta-naphthylamide

L-leucine-beta-naphthylamide (LNA) will support growth of a leucine auxotroph of Salmonella typhimurium. Utilization of this compound depends on the presence in the cells of active peptidase N. Selection for improved growth on a suboptimal concentration of LNA yields mutants some of which contain elevated levels of peptidase N. The properties of these strains indicate that they carry tandem genetic duplication of the pepN locus: they show rec-dependent genetic instability; they contain an approximately doubled level of the pepN gene product; neighboring chromosomal loci are also duplicated; and, the mutants occur with a greatly diminished frequency in rec- strains. When selection for improved growth on LNA is applied to a rec- strain, the mutants obtained do not contain duplications. These strains appear to contain lesions in the pepN gene that lead to the production of a peptidase N with altered substrate specificity.

Multiple molecular forms of human alanine aminopeptidase: immunochemical properties

Human pancreas, kidney, and liver alanine aminopeptidases have similar if not identical antigenic determinants even though these three isoenzymes have distinctly different electrophoretic mobilities. Single precipitin lines without spur formation were obtained for all three enzymes with antisera obtained from rabbits immunized with these three purified enzymes. Treatment of these enzymes with neuraminidase eliminated the differences in their electrophoretic migration on polyacrylamide gels and on agarose immunoelectrophoresis gels. Treatment of the pancreas, kidney, and liver alanine aminopeptidases with their respective antibodies yielded enzymes that displayed non-competitive inhibition when the dependence of velocity upon substrate concentration was determined for each enzyme, i.e. the antibodies did not cause a change in the Km values obtained in the absence of the antibody whereas kcat was reduced to the same extent for each enzyme. The removal of sialic acid(s) from these enzymes did not alter their immunochemical characteristics or their kinetic characteristics.

Purification and properties of human intestine alanine aminopeptidase

Human intestinal alanine aminopeptidase has been purified to greater than 90% homogeneity. The enzyme was released from mucosal cell membranes by Triton X-100 treatment. The native enzyme had a molecular weight of 206,000 in dilute buffer and 108,000 in the presence of sodium dodecyl sulfate. The enzyme was inhibited by chelators suggesting the presence of a metal ion in the enzyme. The most potent chelator inhibitor tested, o-phenanthroline, gave mixed kinetics (Ki = 67 micro M). Activity was restored by removal of the chelator. The enzyme was inhibited competitively by amino acids having hydrophobic side chains such as L-phenylalanine (Ki = 0.67 mM). Puromycin and methicillin also inhibited the enzyme in the competitive (Ki = 12.5 micro M) and noncompetitive (Ki = 4.6 mM) manner, respectively. Kinetic analysis of several amino acid beta-naphthylamides as substrates demonstrated the preference for substrates having hydrophobic or basic amino terminal residues with no beta-branching. L-Methionyl-beta-naphthylamide was the most tightly bound with L-alanyl-beta-naphthylamide was the most rapidly hydrolyzed.

Peptidase activities in the functioning jejunum and ileum before and after jejunoileal bypass in morbid obesity

Different peptidase activities were studied preoperatively and postoperatively on intestinal biopsy specimens from patients with jejunoileal bypass for morbid obesity. Preoperatively the activities of the brush border peptidases, microvillus aminopeptidase (EC 3.4.11.2) and dipeptidyl peptidase IV (EC 3.4.14.X), were lowest at the ligament of Treitz and highest in the distal ileum. The activity of the other brush border peptidase studied, the gamma-glutamyl transpeptidase (EC 2.3.2.2), had a maximum at proximal jejunum, like the two cytosol dipeptidases glycyl-leucine dipeptidase (EC 3.4.13.2) and proline dipeptidase (EC 3.4.13.9). Postoperative changes in peptidase activities were most pronounced in the ileal part of the shunt, whereas changes were small in the jejunal part. The most conspicuous finding was a significant increase in gamma-glutamyl transpeptidase activity in the ileum. There was also tendency to an increase of the cytosol dipeptidases in the ileum. In contrast, the activity of microvillus aminopeptidase and dipeptidyl peptidase IV in the ileum had a tendency to decrease.

Immunoelectrophoretic studies on pig intestinal brush border proteins

Brush borders were prepared from pig intestinal mucosa and the membrane proteins solubilized with either Triton X-100 or papain. Proteins, thus released, were used as antigens to raise antisera in rabbits. The immunoglobulin G fractions were isolated and shown by the double layer immunofluorescence staining technique to react only with the brush border region of the enterocyte. The antibodies obtained were used in immunoelectrophoretic studies on the brush border proteins. Eight hydrolytic activities were identified by the use of histo-chemical staining methods. These were the microsomal aminopeptidase (EC 3.4.11.2), aspartate aminopeptidase (EC 3.4.11.7), dipeptidyl peptidase IV (EC 3.4.14.X), lactase (EC 3.2.1.23), glucoamylase (EC 3.2.1.3), sucrase (EC 3.2.1.48), isomaltase (EC 3.2.1.10) and alkaline phosphatase (EC 3.1.3.1). In addition, at least four faint immunoprecipitates were formed but none of these were identified.

Effect of pH on substrate and inhibitor kinetic constants of human liver alanine aminopeptidase. Evidence for two ionizable active center groups

The presence of at least two ionizable active center groups has been detected by a study of the effect of pH upon catalysis of hydrolysis of L-alanyl-beta-naphthylamide by human liver alanine aminopeptidase and upon the inhibition of hydrolysis by inhibitors and substrate analogs. Octanoic acid, octylamine, and peptide inhibitors have been found to be competitive inhibitors and are therefore thought to bind the active center. L-Phe was previously shown to bind the active center since it was found to be a competitive inhibitor of the hydrolysis of tripeptide substrates (Garner, C. W., and Behal, F. J. (1975), Biochemistry 14, 3208). A plot of pKm vs. pH for the substrate L-Ala-beta-naphthylamide showed that binding decreased below pH 5.9 and above 7.5, the points at which the theoretical curve undergoes an integral change in slope. These points are interpreted as the pKa either of substrate ionizable groups or binding-dependent enzyme active center groups. Similar plots of pKm vs. pH for L-alanyl-p-nitroanilide (as substrate) and pKi vs. pH for L-Leu-L-Leu-L-Leu and D-Leu-L-Tyr (as inhibitors) gave pairs fo pKa values of 5.8 and 7.4, 6.0 and 7.5, and 5.7 and 7.5, respectively. All the above substrates (and D-Leu-L-Tyr) have pKa values near 7.5; therefore, the binding-dependent group with a pKa value near 7.5 is possibly this substrate group. Similar plots of pKi vs. pH for the inhibitors L-Phe, L-Met, L-Leu, octylamine, and octanoic acid had only one bending point at 7.7, 7.6, 7.4, 6.3, and 5.9, respectively. Amino acid inhibitors, octylamine, and octanoic acid have no groups with pKa values between 5 and 9. These data indicate that there are two active center ionizable groups with pKa values of approximately 6.0 and 7.5 which are involved in substrate binding or inhibitory amino acid binding but not in catalysis since Vmax was constant at all pH values tested.

Characterization of an inducible amidase from Pseudomonas acidovorans AE1

The main molecular and catalytic properties of an acetanilide-hydrolyzing enzyme from Pseudomonas acidovorans AE 1, purified to a homogeneous state, were investigated. The molecular weight was 57 500 as determined by gel filtration and 55 300 as computed from the amino acid composition. By polyacrylamide gel electrophoresis in dodecylsulfate a polypeptide chain weight of 56 700 was obtained. Based on the reaction of the highly purufied enzyme with diethyl-4-nitrophenyl phosphate an equivalent weight of approximately 59 100 was found. From these results it was concluded that the enzyme consists of a single polypeptide chain and contains one active site per molecule. The enzyme hydrolyzed esters as well as certain aromatic amides. It also catalysed the transfer of acetyl groups to phenetidine yielding phenacetin. The activities towards aliphatic esters were much smaller. The enzyme was stable at pH values ranging from 7 to 9 and its pH-optimum was about 10. It was strongly inhibited by organophosphorous compounds, like diethyl-4-nitrophenyl phosphate or diisopropylphosphorofluoridate, as well as by physostigmine sulfate and -SH-blocking reagents, like HgCl-2 or 4-chloromercuribenzoic acid. o-Nitrophenol caused a competitive inhibition and phenetidine an uncompetitive inhibition.

Pptidase activities in group N streptococci

Several peptidase activites in the 3 species of Group N streptococci were partly separated by gel filtration on Sephadex G-200. The peptidases identified were a general aminopeptidase of wide specificity, a tripeptidase, a proline iminopeptidase (prolyl-beta-napthylamidase), a proline iminodipeptidase and an aminopeptidase-P. The effects of temperature and pH on the stability of the enzyme activities, and the influence of the type of N source used in the growth medium on the elution pattern of the enzymes were examined.

Peptidase mutants of Salmonella typhimurium

Six peptidase activities have been distinguished electrophoretically in cell extracts of Salmonella typhimurium with the aid of a histochemical stain. The activities can also be partially separated by chromatography on diethylaminoethyl-cellulose. These peptidases show overlapping substrate specificities. Mutants (pepN) of the parent strain leu-485 lacking one of these enzymes (peptidase N) were obtained by screening for colonies that do not hydrolyze the chromogenic substrate l-alanyl-beta-naphthylamide. The absence of this broad-specificity peptidase in leu-485 pepN(-) mutants allowed the selection of mutants unable to use l-leucyl-l-alaninamide as a leucine source. These mutants (leu-485 pepN(-)pepA(-)) lack a broad-specificity peptidase (peptidase A) similar to aminopeptidase I previously described in Escherichia coli. Mutants (pepD) lacking a dipeptidase (peptidase D) have been isolated from a leu-485 pepN(-)pepA(-) parent by penicillin selection for mutants unable to use l-leucyl-l-glycine as a leucine source. Mutants (pepB) lacking a fourth peptidase (peptidase B) have been isolated from a leu-485 pepN(-)pepA(-)pepD(-) strain by penicillin selection for failure to utilize l-leucyl-l-leucine as a source of leucine. Single recombinants were obtained by transduction for each of the peptidases missing in a leu-485 pepN(-)pepA(-)pepD(-)pepB(-) strain. The growth response of these recombinants to leucine peptides shows that all of these peptidases can function in the catabolism of peptides and that they display overlapping substrate specificities in vivo.