Characterization of aminopeptidases in human kidney soluble fraction

Activity profiling of aminopeptidases in cell lysates using a fluorogenic substrate library

Aminopeptidases are exopeptidases that process peptide bonds at the N-terminus of protein substrates, and they are involved in controlling several metabolic pathways. Due to their involvement in diseases such as cancer or rheumatoid arthritis, their presence can also be used as a predictive biomarker. Here, we used a library of fluorogenic substrates containing natural and unnatural amino acids to reliably measure the aminopeptidase N (APN) activity in cell lysates obtained from human, pig and rat kidneys. We compared our results to the substrate specificity profile of isolated APN. Our data strongly support the observation that fluorogenic substrates can be successfully used to identify aminopeptidases and to measure their activity in cell lysates. Moreover, in contrast to assays using single substrates, which can result in overlapping specificity due to cleavage by several aminopeptidases, our library fingerprint can provide information about single enzymes.

Metal promiscuity and metal-dependent substrate preferences of Trypanosoma brucei methionine aminopeptidase 1

Methionine aminopeptidases play a major role in posttranslational protein processing and are therefore promising targets for the discovery of novel therapeutical agents. We here describe the heterologous expression, purification, and characterization of recombinant Trypanosoma brucei methionine aminopeptidase, type 1 (TbMetAP1). We investigated the dependency of TbMetAP1 activity on pH and metal cofactor (type and concentration) using in particular the substrates Met-Gly-Met-Met and Met-AMC along with related compounds, and determined kinetic values (Km, vmax, kcat). The optimal pH for TbMetAP1 activity is between 7.0 and 8.0. Surprisingly, the two substrates have different cofactor requirements: Both substrates are processed by the cobalt-activated TbMetAP1, but only the Met-Gly-Met-Met substrate is processed with nearly identical catalytical properties by the zinc-activated enzyme. Depending on the substrate, various other metal ions (iron(II), manganese, nickel) were also accepted as cofactors. Two aspects of this work are relevant for the biochemistry of MetAPs and further drug discovery efforts: 1. Zinc, and not cobalt ions are probably the physiological cofactor of TbMetAP1 and possibly other MetAPs. 2. In MetAP assays for compound screening, the combination of the Met-AMC substrate with cobalt, manganese or iron ions may not represent the physiological reality, thereby leading to results that can not be extrapolated towards a phenotypic effect.

Altered peptidase activities in thyroid neoplasia and hyperplasia

Background. Papillary thyroid carcinoma (PTC), follicular thyroid adenoma (FTA), and thyroid nodular hyperplasia (TNH) are the most frequent diseases of the thyroid gland. Previous studies described the involvement of dipeptidyl-peptidase IV (DPPIV/CD26) in the development of thyroid neoplasia and proposed it as an additional tool in the diagnosis/prognosis of these diseases. However, very little is known about the involvement of other peptidases in neoplastic and hyperplastic processes of this gland. Methods. The catalytic activity of 10 peptidases in a series of 30 PTC, 10 FTA, and 14 TNH was measured fluorimetrically in tumour and nontumour adjacent tissues. Results. The activity of DPPIV/CD26 was markedly higher in PTC than in FTA, TNH, and nontumour tissues. Aspartyl aminopeptidase (AspAP), alanyl aminopeptidase (AlaAP), prolyl endopeptidase, pyroglutamyl peptidase I, and aminopeptidase B activities were significantly increased in thyroid neoplasms when compared to nontumour tissues. AspAP and AlaAP activities were also significantly higher in PTC than in FTA and TNH. Conclusions. These data suggest the involvement of DPPIV/CD26 and some cytosolic peptidases in the neoplastic development of PTC and FTA. Further studies will help to define the possible clinical usefulness of AlaAP and AspAP in the diagnosis/prognosis of thyroid neoplasms.

The impact of peptidase activity on clear cell renal cell carcinoma survival

Several studies have proposed that protease expression and activity may have a predictive value in the survival of clear cell renal cell carcinoma (CCRCC). Most efforts on this issue have been focused on the analysis of matrix metalloproteinases (MMP) and very little on the role of other proteases, such as peptidases. The catalytic activity of 9 peptidases (APN, APB, ASP, CAP, DPP-IV, NEP/CD10, PEP, PGI, and PSA) was quantified by fluorometric methods in a series of 79 CCRCC patients, and the results obtained were analyzed for survival (Kaplan-Meier curves, log-rank test, and Cox multivariate analysis). CCRCC patients with higher activity levels of membrane-bound APN and soluble APN, DPP-IV, and CAP had significantly shorter 5-yr survival rates than those with lower levels. By contrast, higher soluble APB activity significantly correlated with longer survival. Our data suggest the involvement of peptidases in the biological aggressiveness of CCRCC and support the usefulness of measuring these proteases to assess the prognosis of patients with CCRCC.

Activity of soluble aminopeptidase A and dipeptidyl peptidase IV and membrane-bound aminopeptidase B and pyroglutamyl peptidase I in adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis

OBJECTIVE

To analyze soluble and membrane-bound peptidase activities in the tonsils and adenoids removed from patients with adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis.

METHODS

A total of 48 tissue samples from patients undergoing adenoidectomy and tonsillectomy for adenoid hyperplasia, tonsillar hyperplasia or chronic tonsillitis were analyzed. The catalytic activity of a pool of peptidases in the soluble (dipeptidyl peptidase IV, aminopeptidase A, aminopeptidase N and cystinyl aminopeptidase) and membrane-bound (prolyl endopeptidase, aspartyl aminopeptidase, aminopeptidase B and pyroglutamyl peptidase I) fractions was measured fluorometrically.

RESULTS

The activity of membrane-bound aminopeptidase B was higher in cases of chronic tonsillitis and adenoid hyperplasia than in tonsillar hyperplasia, p=0.004. Soluble dipeptidyl peptidase IV and membrane-bound pyroglutamyl peptidase I were found to be more active in tissues from male chronic tonsillitis tissues, p<0.05, while membrane-bound aminopeptidase B activity was higher in tissues of females with tonsillar hyperplasia, p<0.001. In the case of chronic tonsillitis, soluble aminopeptidase A was found to have a higher level of activity in tissues from children than those from adults, p=0.005.

CONCLUSIONS

Our results suggest a potential role of soluble aminopeptidase A, soluble dipeptidyl peptidase IV, membrane-bound aminopeptidase B and membrane-bound pyroglutamyl peptidase I in the pathobiology of adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis that is differently regulated as a function of gender. These finfings may modify in the future the clinical approach to these diseases.

Altered dipeptidyl peptidase IV and prolyl endopeptidase activities in chronic tonsillitis, tonsillar hyperplasia and adenoid hyperplasia

OBJECTIVE

To analyse peptidase activities in the removed tonsils and adenoids from patients with chronic tonsillitis, tonsillar hyperplasia and adenoid hyperplasia.

METHODS

We have analyzed 48 tissue samples from patients undergoing tonsillectomy and adenoidectomy for chronic tonsillitis, tonsillar hyperplasia or adenoid hyperplasia. Tonsillectomy and adenoidectomy samples were collected and frozen for later enzyme analysis. The catalytic activity of a pool of peptidases (dipeptidyl peptidase IV, prolyl endopeptidase, aminopeptidase A, aminopeptidase N, aspartyl aminopeptidase, aminopeptidase B, neutral endopeptidase, pyroglutamyl peptidase I, puromycin-sensitive aminopeptidase and cystinyl aminopeptidase) was measured fluorometrically.

RESULTS

The activity of prolyl endopeptidase was higher in tonsillar hyperplasia and adenoid hyperplasia than in chronic tonsillitis. On the contrary, dipeptidyl peptidase IV activity was higher in chronic tonsillitis than in hypertrophic tissues. When data were stratified by age and gender, dipeptidyl peptidase IV was also found to be more active in adult and male chronic tonsillitis tissues. Inversely, dipeptidyl peptidase IV activity was higher in tissues of females with tonsillar hyperplasia.

CONCLUSIONS

These data indicate the involvement of dipeptidyl peptidase IV and prolyl endopeptidase in the mechanisms underlying chronic tonsillitis, tonsillar hyperplasia and adenoid hyperplasia.

Acid, basic, and neutral peptidases present different profiles in chromophobe renal cell carcinoma and in oncocytoma

Renal cell carcinomas (RCCs) are neoplasias with high prevalence and mortality. We previously reported that several peptidases may be involved in the pathophysiology of clear cell renal cell carcinoma (CCRCC). Now, to gain insight into the reasons that lead the various RCC types to behave very differently with regard to aggressiveness and response to anticancer treatments, we analyzed subsets of chromophobe renal cell carcinoma (ChRCC), and renal oncocytoma (RO), a benign tumor; as well as different grades and stages of CCRCCs. Particulate APN, APB, and APA activities were decreased in both ChRCC and RO (tumor vs. nontumor tissues). Interestingly, activities were downregulated in a tumor-type specific way and the intensities of the decreases were stronger in the benign tumor than in the malignant type. Moreover, when two key histopathological parameters for tumor prognosis (high vs. low stage and grade) were analyzed, increases of activity were also observed in several of these cell surface peptidases (APN, APB). Some soluble activities (APB, Asp-AP) were also downregulated in the RCCs. With respect to genetic expression, PSA and APN were in a positive correlation related to their activities in both ChRCC and RO; but not APB, Asp-AP, APA, and PGI. These results may suggest an involvement of several peptidases in the pathophysiology of renal cancer, since they presented different patterns of activity and expression in tumors with different behaviors.

Altered levels of acid, basic, and neutral peptidase activity and expression in human clear cell renal cell carcinoma

Peptides play important roles in cell regulation and signaling in many tissues and are regulated by peptidases, most of which are highly expressed in the kidney. Several peptide convertases have a function in different tumor stages, and some have been clearly characterized as diagnostic and prognostic markers for solid tumors, including renal cancer; however, little is known about their in vivo role in kidney tumors. The present study compares the activity of a range of peptidases in human tumor samples and nontumor tissue obtained from clear cell renal cell carcinoma (CCRCC) patients. To cover the complete spectrum and subcellular distribution of peptide-converting activity, acid, neutral, basic, and omega activities were selected. CCRCC displays a selective and restricted pattern of peptidase activities. Puromycin-sensitive aminopeptidase activity in the tumor increases [tumor (t) = 10,775 vs. nontumor (n) = 7,635 units of peptidase (UP)/mg protein; P < 0.05], whereas aminopeptidase N decreases (t = 6,664 vs. n = 33,381 UP/mg protein; P < 0.001). Aminopeptidase B activity of the particulate fraction in tumors decreases (t = 2,399 vs. n = 13,536 UP/mg protein; P < 0.001) compared with nontumor tissues, and aspartyl-aminopeptidase activity decreases significantly in CCRCC (t = 137 vs. n = 223 UP/mg protein; P < 0.05). Soluble and particulate pyroglutamyl peptidase I activities, aminopeptidase A activity, and soluble aminopeptidase B activity do not vary in renal cancer. The relative expression for the aforementioned peptidases, assayed using quantitative RT-PCR, increases in CCRCC for aminopeptidases B (1.5-fold) and A (19-fold), aspartyl-aminopeptidase (3.9-fold), puromycin-sensitive aminopeptidase (2.5-fold), and pyroglutamyl peptidase I (7.6-fold). Only aminopeptidase N expression decreases in tumors (1.3-fold). This peptidase activity profile in the neoplastic kidney suggests a specific role for the studied convertases and the possible involvement of an intracrine renin-angiotensin system in the pathogenesis of CCRCC.

Ischemia-reperfusion injury in cadaveric nonheart beating, cadaveric heart beating and live donor renal transplants

PURPOSE

Ischemia-reperfusion injury is gaining importance in transplantation as being responsible for allograft dysfunction. Ischemia occurs during kidney procurement, which is shortest in LDs, and prolonged in cadaveric HBDs and NHBDs.

MATERIALS AND METHODS

Renal transplants from 17 LDs, 15 HBDs and 19 NHBDs were assessed during reperfusion for biochemical markers of ischemia-reperfusion injury and assessed clinically. Central venous blood sampling was assayed for free radicals using electron spin resonance and tissue injury biomarkers, namely lactate dehydrogenase, fatty acid binding protein, alanine aminopeptidase, lactate and total antioxidants.

RESULTS

The return to stable renal function was more rapid in LD renal transplants, while recovery continued from 3 months after hospital discharge in NHBD renal transplants. Injury markers, such as lactate dehydrogenase, fatty acid binding protein, alanine aminopeptidase and lactate, were raised at the time of reperfusion, especially in NHBD renal transplants. Free radical release measured by electron spin resonance showed 2 phase release, that is early (0 to 10-minute) and late (20 to 40-minute) release. In NHBD, HBD and LD renal transplants the index of free radical release in the early phase was 1.43, 1.36 and 1.20, and in the late phase it was 1.43, 1.38 and 0.97, respectively (each ANOVA p <0.05).

CONCLUSIONS

NHBD renal transplants were accompanied by a greater release of free radicals at reperfusion (NHBD > HBD > LD), which was associated with an increase in tissue injury markers at reperfusion. This was reflected in a slower return to stable renal function in NHBD compared to HBD and LD renal transplants.

Novel organic nitrate prodrug 4(R)-N-(2-Nitroxyethyl)-2-oxothiazolidine-4-carboxamide (RS-7897) serves as a xenobiotic substrate for pyroglutamyl aminopeptidase I in dogs

RS-7897, a novel organic nitrate, structurally contains aminoethylnitrate (AEN) and L-2-oxothiazolidine-4-carboxylic acid (L-OTCA), which are linked together via an amide bond. Vasodilating activity of RS-7897 was 130 times weaker than that of AEN in vitro, while in vivo it was comparable to but longer lasting than those of AEN and nitroglycerin in anesthetized dogs. Intravenous administration of RS-7897 to dogs resulted in the appearance in plasma of AEN, which decreased with about 2.5 times longer t(1/2) (0.49 h) than that after administration of AEN itself. The T(max) value of AEN (0.25 h) after RS-7897 dosing agreed with the time showing the maximum vasodilating effect, indicating that RS-7897 serves as a prodrug releasing AEN slowly in vivo. The activity to hydrolyze RS-7897 to AEN and L-OTCA was localized in the cytosolic fractions of dog tissues, inhibited by thiol-blocking agents and was strongly inhibited by thyrotropin-releasing hormone, a substrate of pyroglutamyl aminopeptidase I (PAP-I). Furthermore, the RS-7897-hydrolyzing activity in dog liver cytosol was completely inhibited by an antibody against rat PAP-I. Therefore, it was found that PAP-I is involved in bioactivation of RS-7897 by amide bond hydrolysis, recognizing the sulfur-substituted L-pyroglutamyl moiety (L-OTCA) of this xenobiotic substrate.

Hydrolysis of synthetic substrate, L-pyroglutamyl p-nitroanilide is catalyzed solely by pyroglutamyl aminopeptidase I in rat liver cytosol

Pyroglutamyl aminopeptidase I (PAP-I) is a cytosolic cysteine peptidase, which hydrolytically removes the L-pyroglutamate residue from the amino terminus of endogenous proteins and peptides. L-Pyroglutamyl p-nitroanilide serves as the synthetic substrate of this enzyme, while there is a possibility of other hydrolases being involved in the hydrolysis of this xenobiotic substrate. We cloned a full-length cDNA encoding rat PAP-I from a rat liver cDNA library and expressed this cDNA in Escherichia coli to obtain a recombinant PAP-I as a single protein. The cDNA encoded a sequence of 209 amino acids with a calculated molecular weight of 22913 Da. The homology of the deduced amino acid sequence of rat PAP-I was 98.6 and 94.3% to mouse and human PAP-Is, respectively. The biochemical properties of the recombinant rat PAP-I were almost identical to those of the recombinant mouse and human PAP-Is and the purified rat liver cytosolic PAP-I in terms of the molecular weight, subunit structure, affinity to the substrate, inhibitor profile and pH optimum. Immunoblot analysis using an antibody raised against recombinant rat PAP-I showed that rat PAP-I is present almost exclusively in the cytosolic fraction of the rat liver. Moreover, the hydrolyzing activity for L-pyroglutamyl p-nitroanilide in rat liver cytosolic fraction was completely inhibited by the antibody, strongly suggesting that this xenobiotic substrate is hydrolyzed solely by PAP-I.

Purification and properties of an aminopeptidase from the mid-gut gland of scallop (Patinopecten yessoensis)

An aminopeptidase was isolated from the mid-gut gland of Patinopecten yessoensis. The enzyme was purified from an acetone-dried preparation by extracting, ammonium sulfate precipitation, Hi-Load Q column chromatography, isoelectric focusing, and POROS HP2 and HQ column chromatography. The molecular weight of the enzyme was estimated to be 61 kDa by SDS-polyacrylamide gel electrophoresis and 59 kDa by gel permeation chromatography. The isoelectric point of the enzyme was 5.2 and the optimum pH was 7.0 toward leucine p-nitroanilide (Leu-pNA). The enzyme was inhibited by o-phenanthroline. The activity of the enzyme treated with o-phenanthroline was completely recovered by adding excess Zn(2+). Relative hydrolysis rates of amino acid-pNAs and amino acid-4-methylcoumaryl-7-amides (amino acid-MCAs) indicated that the enzyme preferred substrates having Ala or Met as an amino acid residue. The enzyme had a K(m) of 32.2 microM and k(cat) of 29.5 s(-1) with Ala-pNA and a K(m) of 11.1 microM and k(cat) of 9.49 s(-1) with Ala-MCA. The enzyme sequentially liberated amino acids from the amino-termini of Ala-Phe-Tyr-Glu.

Improving the quality of kidneys from non-heart-beating donors, using streptokinase: an animal model

BACKGROUND

Non-heart-beating donors (NHBD) offer a promising potential to increase the cadaveric organ donor pool, especially for kidneys. However, almost half of NHBD kidneys are discarded after viability assessment. This wastage is costly in both human and monetary terms. Intravascular thrombosis at the time of donor death is an event leading to failure in the viability assessment. We have developed an animal model to investigate the effects of the addition of streptokinase to the in situ flush medium before transplant in an attempt to redress the situation.

METHODS

Two groups of eight healthy young Landrace Yorkshire white pigs were entered into the study. Both groups were subjected to approximately 70 min warm ischemia. Both groups received an intravascular flush with 4 L of Marshall's solution with heparin (1000 IU/L); one group of pigs also had streptokinase (1.5 MIU/L) added. After donor nephrectomy, all kidneys were machine perfused for 4 hr. Data on perfusion characteristics were taken and samples of kidney effluent were assayed for tissue damage biomarkers, glutathione S-transferase (GST) and alanine aminopeptidase (Ala-AP). Wedge sections of porcine kidneys were taken at the end of perfusion, for histological analysis.

RESULTS

Data on machine perfusion parameters (temperature, mean pressure index, resistance) indicate better cooling, lower resistance, and lower mean pressure index in the streptokinase-treated group of pigs. GST and Ala-AP levels were increased in the nonstreptokinase group perfusates. Histopathological analysis of porcine kidneys indicated more ischemic injury and tissue damage in the nonstreptokinase group.

CONCLUSION

The use of streptokinase in this porcine NHBD model conferred benefits to donor kidneys when assessed by machine perfusion. Markers of biochemical injury indicated that less renal tissue damage occurred with the incorporation of streptokinase in the in situ flush medium.

Puromycin-sensitive alanyl aminopeptidase from human liver cytosol: purification and characterization

A cytosolic alanyl aminopeptidase (AAP-S) was purified to homogeneity from human liver cytosol. The molecular weight of the purified enzyme was calculated to be approximately 98,000 on TOF-MS and 90,000 on SDS-PAGE in the presence of beta-ME. These findings suggest that the enzyme exists as a monomeric form in human liver cytosol. The enzyme rapidly hydrolyzed the substrates Ala-, Lys- and Phe-MCAs, and moderately hydrolyzed Met-, Leu-, Tyr- and Lys-Ala-MCAs at pH ranging from 7.5 to 8.0. The order of the K(cat)/K(m) values of AAP-S at the optimal pH was Arg->Arg-Arg->Met->Leu->Lys->Phe->Lys-Ala->Tyr->Ala-MCAs. It was strongly inhibited by bestatin, leuhistin, actinonin, amastatin, 1, 10-phenanthroline, DFP, PCMBS, Zn(2+), Cd(2+), Co(2+), Cu((2+)), Hg(2+) and puromycin. AAP-S was approximately 80 times more sensitive than human seminal plasma AAP (aminopeptidase N, membrane type). The amino acid sequence of the first 60 residues of AAP-S was highly homologous with the N-terminal amino acid sequence of the rat liver puromycin-sensitive enkephalin-degrading aminopeptidase. These physicochemical properties and findings indicate that AAP-S from human liver cytosol is identical to those of other puromycin-sensitive aminopeptidase(s). Furthermore, with immunohistochemistry the enzyme was strongly stained in the cytoplasm of liver cells and renal tubules, and was ubiquitously localized in various human tissues.

The crystal structure of pyroglutamyl peptidase I from Bacillus amyloliquefaciens reveals a new structure for a cysteine protease

BACKGROUND

The N-terminal pyroglutamyl (pGlu) residue of peptide hormones, such as thyrotropin-releasing hormone (TRH) and luteinizing hormone releasing hormone (LH-RH), confers resistance to proteolysis by conventional aminopeptidases. Specialized pyroglutamyl peptidases (PGPs) are able to cleave an N-terminal pyroglutamyl residue and thus control hormonal signals. Until now, no direct or homology-based three-dimensional structure was available for any PGP.

RESULTS

The crystal structure of pyroglutamyl peptidase I (PGP-I) from Bacillus amyloliquefaciens has been determined to 1.6 A resolution. The crystallographic asymmetric unit of PGP-I is a tetramer of four identical monomers related by noncrystallographic 222 symmetry. The protein folds into an alpha/beta globular domain with a hydrophobic core consisting of a twisted beta sheet surrounded by five alpha helices. The structure allows the function of most of the conserved residues in the PGP-I family to be identified. The catalytic triad comprises Cys144, His168 and Glu81.

CONCLUSIONS

The catalytic site does not have a conventional oxyanion hole, although Cys144, the sidechain of Arg91 and the dipole of an alpha helix could all stabilize a negative charge. The catalytic site has an S1 pocket lined with conserved hydrophobic residues to accommodate the pyroglutamyl residue. Aside from the S1 pocket, there is no clearly defined mainchain substrate-binding region, consistent with the lack of substrate specificity. Although the overall structure of PGP-I resembles some other alpha/beta twisted open-sheet structures, such as purine nucleoside phosphorylase and cutinase, there are important differences in the location and organization of the active-site residues. Thus, PGP-I belongs to a new family of cysteine proteases.

Pyroglutamyl peptidase: an overview of the three known enzymatic forms

Pyroglutamyl peptidase can be classified as an omega peptidase which hydrolytically removes the amino terminal pyroglutamate (pGlu) residue from specific pyroglutamyl substrates. To date, three distinct forms of this enzyme have been identified in mammalian tissues. Type I is typically a cytosolic, cysteine peptidase displaying a broad pyroglutamyl substrate specificity and low molecular mass. Type II has been shown to be a membrane anchored metalloenzyme of high molecular mass with a narrow substrate specificity restricted to the hypothalamic releasing factor, thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2). A third pyroglutamyl peptidase activity has also been observed in mammalian serum which displays biochemical characteristics remarkably similar to those of tissue Type II, namely a high molecular mass, sensitivity to metal chelating agents, and a narrow substrate specificity also restricted to TRH. This serum activity has subsequently been designated 'thyroliberinase'. This review surveys the biochemical, enzymatic, and structural properties of this interesting and unique class of peptidases. It also addresses the putative physiological roles which have been ascribed to these enzymes. Pyroglutamyl peptidase activities isolated and characterized from bacterial sources are also reviewed and compared with their mammalian counterparts.

Isolation and characterization of an alanyl aminopeptidase from rat liver cytosol as a puromycin-sensitive enkephalin-degrading aminopeptidase

Alanyl aminopeptidase (AAP-S) was purified to homogeneity from rat liver cytosol. The molecular weight of the purified enzyme was calculated to be approximately 100,000 on Sephacryl S-200 HR and to be 90,000 on SDS-PAGE in the presence of beta-mercaptoethanol. These findings suggested that the enzyme exists as a monomeric form in rat liver cytosol. The enzyme rapidly hydrolyzed the substrates Ala-, Tyr- and Met-MCAs, and moderately hydrolyzed Arg-, Lys-, Leu-, Phe- and Lys-Ala-MCAs at pHs ranging from 7.5to 8.0. The enzyme also hydrolyzed several amino acid 4-methyl-coumaryl-7-amide (MCA) substrates. The order for k(cat)/Km values of AAP-S at the optimal pH (pH 7.5) was Lys->Met->Arg->Ala->Leu->Phe->Tyr->Lys-Ala-MCAs. It was strongly inhibited by bestatin, leuhistin, actinonin, amastatin, 1, 10-phenanthroline, PCMBS, Zn2+, Cd2+, Co2+, Cu2+ and Hg2+, and puromycin. The amino acid sequence of the first 43 residues of the enzyme was determined as Pro1-Glu-Lys-Arg-Pro5-Phe-Glu-Arg-Leu-Pro10-Thr-Glu-Val-Ser-Pro 15-Ile-Asn-Tyr-Ser-Leu20-(Cys)-Leu-Lys-Pro-Asp25-Leu-Leu- Asp-Phe-Thr30-Phe-Glu-Gly-Lys-Leu35-Glu-Ala-Ala-Ala-Gln40 -Val-Arg-Gln-. This N-terminal amino acid sequence is almost identical with those of puromycin-sensitive enkephalin-degrading aminopeptidases in rat and human brains, and the mouse neuroblastoma cell line Neuro2A. These findings suggest that the AAP-S from rat liver cytosol is a puromycin-sensitive aminopeptidase. Furthermore, with immunohistochemistry the enzyme was strongly stained in the cytosol of the rat liver cells.

Bovine brain pyroglutamyl aminopeptidase (type-1): purification and characterisation of a neuropeptide-inactivating peptidase

Pyroglutamyl aminopeptidase type-1 (PAP-I) is reported to be a soluble, broad specificity aminopeptidase, capable of removing the pyroglutamic acid (pGlu) residue from the amino terminus of pGlu-peptides (e.g. TRH, LHRH, neurotensin and bombesin). The central aim of this study was to undertake, for the first time, the complete purification and characterisation of a PAP activity observed within the cytosolic fraction of bovine whole brain and to compare the properties of the enzyme with previous findings. A series of chromatographic steps (DEAE-Sepharose, Sephacryl S-200 and Activated Thiol Sepharose 4B) generated a soluble PAP activity purified to near homogeneity with a total active yield of 6.6% The enzyme displayed a native molecular mass of approximately 23,700 Da, which compares well with that value obtained under denaturing conditions via SDS-PAGE (24,000 Da), suggesting that the enzyme exists as a monomer. The expression of PAP activity displayed an absolute requirement for the presence of a disulphide bond-reducing agent such as DTT, whilst optimum activity was observed at pH 8.5. strong inhibition of PAP activity was observed with a number of different agents, including transition metal ions, sulphydryl-blocking agents and 2-pyrrolidone (a pGlu analog). A broad pyroglutamyl substrate specificity, which excludes substrates commencing with the pGlu-Pro bond, was also demonstrated for the bovine brain enzyme. Based on a comparison of these findings with those reported for PAP-I in other mammalian tissues, the soluble PAP activity observed in bovine whole brain can tentatively be classified as a pyroglutamyl aminopeptidase type-1 (EC 3.4.19.3).

The effect of small doses of mercury on the level of selected lysosomal enzymes in the plasma and lymphocytes of sheep

1. The 12-month-old ewes, Slovak Merinos breed, were given 40 mg of mercury daily for 28 days in the form of HgCl2. 2. Administration of mercury had a significant influence on the activity of the investigated lysosomal enzymes in the plasma and lymphocytes of sheep.

A study of a synaptosomal thyrotropin releasing hormone-inactivating pyroglutamate aminopeptidase from bovine brain

Pyroglutamate aminopeptidase type II is a highly specific membrane-bound neuropeptidase that has the ability to remove N-terminal pyroglutamate (Glp) from Thyrotropin Releasing Hormone (Glp-His-Pro-NH2) or very closely related tripeptides or tripeptide amides. In this paper we report on the purification and characterisation of a pyroglutamate aminopeptidase activity from the synaptosomal membranes of bovine brain. The Triton X-100 solubilised enzyme was purified nearly 600-fold by a combination of conventional column chromatography steps with a recovery/yield of 17.0%. Phase-partitioning experiments with Triton X-114 showed the activity to be an integral membrane protein. This detergent-solubilised pyroglutamate aminopeptidase activity was found to have a relative molecular mass of 240 kDa on a calibrated S-200 column. HPLC analysis on a C18 reverse-phase column showed that the purified activity displayed a very narrow substrate specificity cleaving only Thyrotropin Releasing Hormone (TRH) or the very closely related acid-TRH, LHRH (1-3) and the TRH-analogue (methyl-His)-TRH and had a Km of 100 microM for the fluorimetric substrate Glp-His-Pro-methyl-coumarin. The enzyme was inactivated by the metalchelator 1,10-ortho-phenanthroline but showed less sensitivity to EDTA. It also showed some inhibition by thiol protease inhibitors such as iodoacetate and n-ethyl-maleimide. In summary, we have purified a pyroglutamate aminopeptidase from the synaptosomal membrane of bovine brain. This enzyme displays characteristics consistent with it being classified as a PAP type II neuropeptidase with only minor differences from other proteases in this group.

Activation and cytotoxicity of 2-alpha-aminoacyl prodrugs of methotrexate

In an effort to improve the selectivity of the anticancer drug methotrexate (MTX), a series of potential prodrugs in which the 2-amino group was acylated with various alpha-amino acids (as well as L-pyroglutamic acid) was synthesized. Such derivatives are anticipated to be hydrolysed to MTX by appropriate aminopeptidases localized (over-expressed naturally or targeted as anti-tumor antibody conjugates) in the vicinity of the tumor. The L-leucyl, L-valyl, L-isoleucyl, D-alanyl and L-pyroglutamyl derivatives were assessed as to their suitability as prodrugs. Except for the L-pyroglutamyl compound, all derivatives decomposed slowly when incubated in phosphate buffer, pH 7.3; the formation of MTX was minimal. No major differences were observed when serum was included in the incubation medium, except for the L-leucyl compound, which was hydrolysed to MTX. The L-leucyl, L-valyl and L-isoleucyl derivatives were hydrolysed readily to MTX by aminopeptidase M (EC 3.4.11.2), while the L-pyroglutamyl and D-alanyl compounds were activated by pyroglutamate aminopeptidase (EC 3.4.19.3) (from Bacillus amyloliquefaciens) and D-aminopeptidase (from Ochrobactrum anthropi), respectively. When tested for inhibition of the target enzyme dihydrofolate reductase (DHFR; EC 1.5.1.3), 2-L-valyl-MTX showed inhibition two orders of magnitude poorer than that given by MTX, in agreement with the expectation that acylation of the 2-amino group reduces binding to DHFR. After treatment of this derivative with aminopeptidase M, the extent of inhibition correlated with the amount of MTX formed. MTX derivatives alone or in combination with the complementary peptidase were tested for cytotoxicity on murine L1210 cells in culture. The above-listed derivatives were considerably less cytotoxic than MTX, except for the L-leucyl derivative which showed considerable cytotoxicity. When the appropriate exogenous peptidase was included, the cytotoxicity of the activated prodrugs approached that of MTX. These results indicate that 2-L-leucyl-MTX is unsuitable as a prodrug since it is activated prematurely by serum enzymes. Although the L-valyl and L-isoleucyl derivatives do not hydrolyse to MTX in serum and are readily activated, they are not ideal prodrugs since they decompose under physiological conditions; the properties of the decomposition product will have a bearing on the ultimate suitability of these compounds. 2-L-Pyroglutamyl-MTX is the best candidate prodrug, showing stability and ready activation by the appropriate aminopeptidase.

Pyrrolidone carboxyl peptidase (Pcp): an enzyme that removes pyroglutamic acid (pGlu) from pGlu-peptides and pGlu-proteins

Pyrrolidone carboxyl peptidase (EC 3.4.11.8) is an exopeptidase commonly called PYRase, which hydrolytically removes the pGlu-proteins. pGlu also known as pyrrolidone carboxylic acid may occur naturally by an enzymatic procedure or may occur as an artifact in proteins or peptides. The enzymatic synthesis of pGlu suggests that this residue may have important biological and physiological functions. Several studies are consistent with this supposition. PYRase has been found in a variety of bacteria, and in plant, animal, and human tissues. For over two decades, biochemical and enzymatic properties of PYRase have been investigated. At least two classes of PYRase have been characterized. The first one includes the bacterial and animal type I PYRases and the second one the animal type II and serum PYRases. Enzymes from these two classes present differences in their molecular weight and in their enzymatic properties. Recently, the genes of PYRases from four bacteria have been cloned and characterized, allowing the study of the primary structure of these enzymes, and their over-expression in heterelogous organisms. Comparison of the primary structure of these enzymes revealed striking homologies. Type I PYRases and bacterial PYRases are generally soluble enzymes, whereas type II PYRases are membrane-bound enzymes. PYRase II appears to play as important a physiological role as other neuropeptide degrading enzymes. However, the role of type I and bacterial PYRases remains unclear. The primary application of PYRase has been its utilization for some protein or peptide sequencing. Development of chromogenic substrates for this enzyme has allowed its use in bacterial diagnosis.

The significance of aminopeptidases and haematopoietic cell differentiation

Aminopeptidases are a group of enzymes found on the cell surface and in the cytoplasmic compartments of many peripheral blood cell types and their progenitors. Their functional roles include the hydrolysis of several biologically active peptides and growth factors and some have proved to be of diagnostic and prognostic value in leukaemia. These enzymes may also be found in serum as a consequence of non-haematopoietic related diseases and so have been used as indicators of liver damage.

Haematopoietic cells in the bone marrow go through a process of growth and differentiation before being released into the peripheral circulation where they fulfill many functional roles. The enzyme activities of some aminopeptidases have been shown to modulate the growth of these cells. In addition, the activities of these enzymes themselves can be regulated by haematopoietic growth factors. However, the mechanisms that regulate their expression and activity are not fully understood. In this report the current literature has been reviewed for evidence of expression, regulation and clinical significance.

Identification and characterization of aminopeptidases from Aplysia californica

Aminopeptidase activities were identified in extracts of kidney, ovotestis, head ganglia, heart and haemolymph of Aplysia californica. These enzyme preparations hydrolysed [3H][Leu]enkephalin at the Try-1-Gly-2 bond as determined by h.p.l.c. analysis of cleavage products. In all these tissues, enkephalin-degrading aminopeptidase activities were present both in membrane-bound and cytosolic fractions. The bivalent-cation-chelating agent, 1,10-phenanthroline, inhibited kidney membrane aminopeptidase activity with an IC50 of 30 microM, suggesting that this enzyme is a metalloproteinase. The aminopeptidase inhibitor amastatin was the most potent inhibitor of [Leu]enkephalin degradation (IC50 25 nM) by membrane-bound aminopeptidase, and bacitracin, bestatin and puromycin were about 100-1000 times less potent. In contrast with membrane-bound aminopeptidase, the cytosolic form is sensitive to puromycin. Angiotensin-converting enzyme inhibitor had no effect on [Leu]enkephalin degradation by kidney membranes, while the neutral endopeptidase inhibitors were poor inhibitors of the enzymes in this preparation. The Km values of the aminopeptidase in the kidney membranes and cytosolic fractions for the [Leu]enkephalin substrate were 2.4 and 7.4 microM respectively. The aminopeptidase present in the kidney membranes also hydrolysed endogenous Phe-Met-Arg-Phe-amide peptide at the Phe-1-Met-2 bond as well as synthetic alanine p-nitroanilide and leucine p-nitroanilide. When used in a competition assay, these substrates inhibited hydrolysis of [3H][Leu]enkephalin, suggesting that the same enzyme degraded all these substrates. Taken together, these results suggest that Aplysia tissues contain both a membrane-bound aminopeptidase related to the mammalian aminopeptidase N and a cytosolic puromycin-sensitive aminopeptidase.

Comparison of soluble aminopeptidases in human cerebral cortex, skeletal muscle and kidney tissues

In an attempt to elucidate the cellular function of the soluble aminopeptidases (with which the majority of tissue aminopeptidase activity is usually associated) we have determined the distribution and characteristics of these enzymes in three functionally dissimilar human tissues (cerebral cortex, skeletal muscle and kidney cortex), using a systematic experimental approach. Following fractionation of brain, muscle or kidney soluble extracts via anion exchange chromatography, four aminopeptidase enzymes types (alanyl-, arginyl-, leucyl- and pyroglutamyl-) were identified; the absolute and relative activities for corresponding enzymes were similar in each tissue. Following further purification of each enzyme type from each tissue (via liquid chromatography/preparative electrophoresis), corresponding enzyme types were found to have similar characteristics (pH optimum of activity, action of enzyme effectors, substrate specificity and molecular mass). Since the same enzymes, with correspondingly similar distribution and characteristics are present in such functionally dissimilar tissues, it is suggested that the principal role for the soluble aminopeptidases (in contrast to the membrane-associated enzymes, which may function in the catabolism of neuropeptides) is in the final stages of the general intracellular protein catabolism cascade, via hydrolysis of oligopeptide intermediates to free amino acids.

Purification and characterization of leucine-specific aminopeptidase from the soluble fraction of human placenta

A soluble aminopeptidase distinct from two enzymes described previously was isolated from human placenta and some of its properties were investigated. The three aminopeptidases were separated by DEAE-cellulose chromatography. The newly found aminopeptidase exhibits specific hydrolysis of leucine derivatives among various synthetic substrates. However, a broad substrate specificity was observed toward some natural bioactive peptides.

Purification and characterization of leucyl aminopeptidase and pyroglutamyl aminopeptidase from human skeletal muscle

The purification and characterization of leucyl aminopeptidase and pyroglutamyl aminopeptidase from human skeletal muscle are described. The characteristics of leucyl aminopeptidase were as follows: optimum activity was at pH 9.5 in the presence of 5 mmol/l Mg2+ or 0.5 mmol Mn2+. No activation of enzyme activity was obtained following addition of other divalent cations or sulphhydryl reagents. Only the leucyl-AMC and methionyl-AMC derivatives were appreciably hydrolysed. The mol mass was estimated as 280 kDa. Approx. 50% inhibition of activity was obtained following addition of p-hydroxymercuriphenyl sulphonate (10 mumol/l), N-ethyl maleimide (2 mmol/l), o-phenanthroline (5 mmol/l), bacitracin (1 mmol/l), amastatin (1 microgram/ml) and bestatin (0.1 mumol/l); no inhibition of activity was obtained in the presence of phenylmethanesulphonyl fluoride (1 mmol/l), limabean trypsin inhibitor (100 microgram/ml) or pepstatin (100 microgram/ml). The following oligopeptides were hydrolysed by the enzyme: luliberin 7-10, proctolin and [Leu5]enkephalin; oligopeptides not appreciably hydrolysed included neurotensin, angiotensin-I, substance-P and bradykinin. Pyroglutamyl aminopeptidase had the following characteristics: optimum activity was at pH 8.5 in the presence of 1 mmol/l dithiothreitol (an absolute requirement for maintenance of enzyme activity). Maximum activity was obtained in the absence of divalent cations. Only the pyroglutamyl-AMC derivative was appreciably hydrolysed. The mol mass of this enzyme was estimated as 22 kDa. Approximately 50% inhibition of activity was obtained on addition of phenanthroline (4 mmol/l) and antipain (7 microgram/ml); no inhibition of activity was obtained following addition of phenyl methanesulphonyl fluoride (1 mmol/l), limabean trypsin inhibitor (100 microgram/ml) or pepstatin (100 microgram/ml). Only oligopeptides with a pyroglutamyl N-terminal residue (thyroliberin, neurotensin, and luliberin) were hydrolysed by the enzyme.

Characterization of dipeptidyl and tripeptidyl aminopeptidases in human kidney soluble fraction

In an attempt to identify improved biochemical markers for the diagnosis of early kidney damage via urinary analysis of kidney derived enzymes, we have undertaken the systematic identification, quantification and characterization (following purification via anion exchange and gel filtration chromatography, and preparative electrophoresis) of the dipeptidyl and tripeptidyl aminopeptidases in normal human kidney soluble extract (with which the majority of the cellular activity of these enzymes is associated). Four chromatographically separable enzyme types were identified as follows (% relative activity in parentheses): dipeptidyl aminopeptidase I (EC 3.4.14.1; 24%); dipeptidyl aminopeptidase II (EC 3.4.14.2; 8%); dipeptidyl aminopeptidase IV (EC 3.4.14.5; 61%); tripeptidyl aminopeptidase (unclassified; 7%). Comparison of the levels of activity for the above enzyme types in normal and pathological urine may lead to an improvement upon existing procedures for the early detection of renal damage.