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PubMed1989

Comparison of major cortical aminopeptidase activity in normal brain and brain from patients with Alzheimer's disease.

In order to develop a greater understanding of the importance of peptide catabolism in the intracellular protein degradation process in normal and pathological human brain, we have undertaken a systematic investigation of the aminopeptidase group of enzymes. Although a wide range of aminoacyl-7-amino-4-methylcoumarin derivatives (which are used to measure aminopeptidase activity) were hydrolysed by normal human cortical soluble extract, fractionation of the latter via anion exchange and gel filtration chromatography resolved only 4 separable aminopeptidase types (activity relative to alanyl aminopeptidase in parenthesis): alanyl (EC 3.4.11.14, 100%); arginyl (2 isoenzymes, EC 3.4.11.6, 15%); pyroglutamyl (EC 3.4.19.3, 4%); and leucyl (EC 3.4.11.1, 1%). Thus approx. 80% of the total soluble aminopeptidase activity in normal human cerebral cortex can be accounted for by a single enzyme, the major cortical aminopeptidase. The activity of this enzyme was measured in the soluble fraction prepared from 4 cortical regions (occipital, frontal, temporal and parietal) in a series of 8 patients with Alzheimer's disease and compared with corresponding data in 8 control normal patients. Although enzyme activity varied in these cortical regions, the activity in corresponding brain areas in the Alzheimer's disease and normal groups was very similar. These findings suggest that the characteristic neurodegeneration associated with Alzheimer's disease does not result from altered activity of the major cortical aminopeptidase in the cortical tissue of patients with this disorder.

Aged↗

PubMed1985

Possible involvement of aminopeptidase, an ecto-enzyme, in the inactivation of bradykinin by intact neutrophils.

The subcellular localization of the bradykinin-inactivating activity was studied using guinea-pig neutrophils and the following results were obtained. The bradykinin-inactivating activities were found to be present in the cytosol and membrane fractions but not in the granular and nuclear fractions. The bradykinin-inactivating activity of the cytosol fraction was inhibited by N-carbobenzoxy-Gly-Pro, an inhibitor of prolyl endopeptidase, whereas that of the membrane fraction was inhibited by bestatin, an inhibitor of aminopeptidase. Prolyl endopeptidase and aminopeptidase activities were located predominantly in the cytosol and membrane fractions, respectively, and their activities were inhibited by their respective inhibitors. Prolyl endopeptidase and aminopeptidase activities measured with synthetic substrates were competitively inhibited by bradykinin, suggesting that bradykinin is a possible substrate for prolyl endopeptidase and aminopeptidase. Intact neutrophils inactivated bradykinin rapidly. However, when neutrophils were modified chemically by diazotized sulfanilic acid, a poorly permeant reagent which inactivates ecto-enzymes selectively, both the bradykinin-inactivating activity and aminopeptidase activity of neutrophils decreased significantly without any inhibition of cytosol prolyl endopeptidase. The possibility that aminopeptidase, an ecto-enzyme, would be responsible for the inactivation of bradykinin by intact neutrophils was deduced from the results above, although both cytosol prolyl endopeptidase and membrane aminopeptidase could inactivate bradykinin.

Aminopeptidases↗

PubMed1988

The occurrence of aminopeptidase N and desquamated cell proteins in intestinal perfusate of the rat.

The in vivo release of a microvillar enzyme, aminopeptidase N (EC 3.4.11.2), and a cytosolic enzyme, lactate dehydrogenase (EC 1.1.1.27), into the intestinal lumen was measured to gain information on the fraction of desquamated cell protein in intestinal juice and on the mechanism of release of intestinal microvillar enzymes. 1.6% and 2.9% of the mucosal activities of aminopeptidase N and lactate dehydrogenase were released to the intestinal lumen per hour, respectively. The ratios between aminopeptidase N and lactate dehydrogenase in intestinal perfusates and mucosal homogenates were similar. This result is compatible with the view that aminopeptidase N in the rat small intestine is predominantly released into the intestinal lumen by desquamation of enterocytes. This conclusion was supported by the failure to demonstrate microvesiculation of the microvilli by electron microscopy. 30-40% of the aminopeptidase N in the intestinal lumen is membrane-bound indicating that partial solubilization occurs during desquamation. The addition of calcium ions did not augment the release of aminopeptidase N or the membrane-bound fraction in the lumen. 10-20% of the protein content in the intestinal lumen is due to extruded cell protein. This includes aminopeptidase N which constitutes 1% of the luminal protein.

Aminopeptidases↗

PubMed2005

Representative aminopeptidases and prolyl endopeptidase from murine macrophages: comparative activity levels in resident and elicited cells.

Macrophages are considered the main effector cells of immune system. Under stimulation these cells are known to be activated by a process involving morphological, biochemical and functional changes. Since altered peptidase activities could be among the factors leading to the differentiation and activation of these cells, in the present work seven naphthylamide derivative substrates were employed to assess representative aminopeptidase and prolyl endopeptidase activities in resident and elicited macrophages of mice. Soluble basic aminopeptidase and prolyl endopeptidase and soluble and particulate neutral and prolyl dipeptidyl aminopeptidase IV activities were present at measurable levels while particulate prolyl endopeptidase and basic aminopeptidase, and particulate and soluble cystyl and pyroglutamyl aminopeptidases were not detectable. Kinetic parameters, chloride activation and the inhibitory effects of puromycin, bestatin, amastatin and diprotin A characterized differential properties of these peptidase activities. The observed increment (about 6-17-fold) of the soluble basic aminopeptidase and prolyl endopeptidase and soluble and particulate neutral and prolyl dipeptidyl aminopeptidase IV activities in elicited macrophages was particularly relevant, as these might contribute to an increased ability of this cell to inactivate several susceptible substrates known to be inflammatory and/or immunological mediators.

Aminopeptidases↗

PubMed2005

Cystyl aminopeptidase activity in the plasma, viscera and brain of the snake Bothrops jararaca.

The relationship between plasma osmolality and cystyl aminopeptidase was characterized in the snake Bothrops jararaca and comparisons were made with the emerging picture of this relationship in rats. The profile of cystyl aminopeptidase activity under basal conditions was determined in the soluble and membrane-bound forms in visceral organs and in the central nervous system in comparison with that of alanyl aminopeptidase. The regional localization of cystyl and alanyl aminopeptidase activities was studied in the central nervous system. The basal level of plasma cystyl aminopeptidase, four- to six-fold higher than in rats, suggests its importance to help regulate circulating levels of neurohypophysial peptides in B. jararaca snake. The osmotic sensitivity of this plasma enzyme, undetectable in male, but about three-fold higher in female snakes than in rats, reveals a sexual dimorphism. In marked contrast to those observed in rats, low levels of soluble and particulate forms in the kidney indicate that cystyl aminopeptidase plays a minor metabolizing role at this anatomical location in B. jararaca. Despite of the regional-specific divergence between the levels of rat and snake enzymes, the bilaterally symmetric pattern of the diencephalic distribution of alanyl aminopeptidase reflects functional homologies between these two distantly related species.

Animals↗

PubMed2000

The role of amino acid residues in the active site of a midgut microvillar aminopeptidase from the beetle Tenebrio molitor.

Aminopeptidases are major enzymes in the midgut microvillar membranes of most insects and are targets of insecticidal Bacillus thuringiensis crystal delta-endotoxins. Sequence analysis and substrate specificity studies showed that these enzymes resemble mammalian aminopeptidase N, although information on the organization of their active site is lacking. The effect of pH at different temperatures on the kinetic parameters of Tenebrio molitor (Coleoptera) larval aminopeptidase showed that enzyme catalysis depend on a deprotonated (pK 7.6; DeltaH degrees (ion), 7.6 kJ/mol) and a protonated (pK 8.2; DeltaH degrees (ion), 16.8 kJ/mol) group. 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide and diethylpyrocarbonate inactivate the enzyme by modifying a pK 5.8 carboxylate and a imidazole group, respectively, with a reaction order around 1. Tetranitromethane changes the K(m) of the enzyme without affecting its V(max) by modifying a phenol group. The presence of a competitive inhibitor decrease the inactivation reaction rates in all these cases. EDTA inactivation of the aminopeptidase is affected by pH and temperature suggesting the involvement in metal binding of at least one deprotonated imidazole group (pK 5.8, DeltaH degrees (ion), 20 kJ/mol). The data support the hypothesis that T. molitor aminopeptidase catalysis depends on a catalytic metal and on a carboxylate and a protonated imidazole group, whereas substrate binding relies in one phenol and one carboxylate groups. The insect aminopeptidase shares common features with mammalian aminopeptidase N, although differing in details of substrate binding and in residues directly involved in catalysis.

Amino Acids↗

PubMed1985

Identification of aminopeptidase M as an enkephalin-inactivating enzyme in rat cerebral membranes.

Two membrane-bound enkephalin-hydrolyzing aminopeptidase activities were partially purified from rat brain membranes. The first, which represents 90% of the total activity, was highly sensitive to both puromycin (Ki = 1 microM) and bestatin (Ki = 0.5 microM). The second was inhibited much more by bestatin (Ki = 4 microM) than by puromycin (Ki = 100 microM). The latter puromycin-insensitive aminopeptidase was found to resemble aminopeptidase M purified from rat kidney brush border membranes. Both displayed the same purification pattern and the same kinetic constants of substrates and inhibitors, and both were similarly inactivated by metal chelating agents. Moreover, antibodies raised in rabbits against rat kidney aminopeptidase M inhibited the aminopeptidase activities of both kidney and brain puromycin-insensitive enzymes at similar dilutions, while the brain puromycin-sensitive aminopeptidase activity was not affected. Thus, aminopeptidase M (EC 3.4.11.2) was found to occur in brain, and the role of this enzyme in inactivating endogenous enkephalins released from their neuronal stores is suggested.

Aminopeptidases↗

PubMed2005

Overexpression of leucyl aminopeptidase in Plasmodium falciparum parasites. Target for the antimalarial activity of bestatin.

Malaria aminopeptidases are important in the generation and regulation of free amino acids that are used in protein anabolism and for maintaining osmotic stability within the infected erythrocyte. The intraerythrocytic development of malaria parasites is blocked when the activity of aminopeptidases is specifically inhibited by reagents such as bestatin. One of the major aminopeptidases of malaria parasites is a leucyl aminopeptidase of the M17 family. We reasoned that, when this enzyme was the target of bestatin inhibition, its overexpression in malaria cells would lead to a reduced sensitivity to the inhibitor. To address this supposition, transgenic Plasmodium falciparum parasites overexpressing the leucyl aminopeptidase were generated by transfection with a plasmid that housed the full-length gene. Transgenic parasites expressed a 65-kDa protein close to the predicted molecule size of 67.831 kDa for the introduced leucyl aminopeptidase, and immunofluorescence studies localized the protein to the cytosol, the location of the native enzyme. The product of the transgene was shown to be functionally active with cytosolic extracts of transgenic parasites exhibiting twice the leucyl aminopeptidase activity compared with wild-type parasites. In vitro inhibitor sensitivity assays demonstrated that the transgenic parasites were more resistant to bestatin (EC50 64 microM) compared with the parent parasites (EC50 25 microM). Overexpression of genes in malaria parasites would have general application in the identification and validation of targets for antimalarial drugs.

Animals↗

PubMed1994

Gene cloning and characterization of PepC, a cysteine aminopeptidase from Streptococcus thermophilus, with sequence similarity to the eucaryotic bleomycin hydrolase.

Streptococcus thermophilus CNRZ 302 contains at least three general aminopeptidases able to hydrolyze Phe-beta-naphthylamide substrate. The gene encoding one of these aminopeptidases was cloned from a total DNA library of S. thermophilus CNRZ 302 constructed in Escherichia coli TG1 using pBluescript plasmid. The wild-type TG1 strain, although not deficient in aminopeptidase activity, is unable to hydrolyze the substrate Phe-beta-naphthylamide, and thus the library could be screened with an enzymic plate assay using this substrate. One clone was selected which was shown to express an aminopeptidase, identified as a PepC-like enzyme on the basis of cross-reactivity with polyclonal antibodies directed against the lactococcal PepC cysteine aminopeptidase. The gene was further subcloned and sequenced. A complete open reading frame coding for a 445-residue (50414 Da) polypeptide was identified. 70% identity was found between the deduced amino acid sequence and the sequence of PepC from Lactococcus lactis subspecies cremoris, confirming the identity of the cloned gene. High sequence similarity (38% identity) was also found with an eucaryotic enzyme, bleomycin hydrolase. In addition, the predicted amino acid sequence of the streptococcal PepC showed a region of strong similarity to the active site of cysteine proteinases with conservation of the residues involved in the catalytic site. The product of the cloned pepC gene was overproduced in E. coli and was purified from a cellular extract. Purification to homogeneity was achieved by two-step ion-exchange chromatography. Biochemical characterization of the pure recombinant enzyme confirms that the cloned peptidase is a thiol aminopeptidase possessing a broad specificity. The enzyme has a molecular mass of 300 kDa suggesting an hexameric structure. On the basis of sequence similarities as well as common biochemical and enzymic properties, the bacterial PepC-type enzymes and the eucaryotic bleomycin hydrolase constitute a new family of thiol aminopeptidases among the cysteine peptidases.

Amino Acid Sequence↗

PubMed1997

Cloning and characterization of Manduca sexta and Plutella xylostella midgut aminopeptidase N enzymes related to Bacillus thuringiensis toxin-binding proteins.

We report the purification, cloning and characterization of an aminopeptidase N from the midgut epithelium of Manduca sexta that binds Cry1Ab5, an insecticidal crystal protein [ICP] from Bacillus thuringiensis. Sequence information derived from this M. sexta aminopeptidase N was used for the cloning of an aminopeptidase N from the midgut brush-border membrane of Plutella xylostella, an insect species of which some populations acquired resistance against Cry1Ab5. Affinity chromatography on a Cry1Ab5 matrix was used to isolate a 120-kDa glycoprotein from the larval midgut of the lepidopteran M. sexta. On ligand blots the purified 120-kDa protein discriminates between the lepidopteran-specific Cry1Ab5 and the coleopteran-specific Cry3A delta-endotoxin. Internal amino acid sequences from the 120-kDa protein were used for the design of degenerate oligonucleotides. From a nested PCR with M. sexta midgut cDNA as template, a DNA fragment was obtained which shows similarity to prokaryotic and eukaryotic aminopeptidase N genes. This PCR fragment was used to screen cDNA libraries of larval midguts from M. sexta and P. xylostella. From the M. sexta midgut cDNA library a 2973-bp nucleotide sequence was cloned. The ORF of the sequence encodes a 942-residue aminopeptidase N (M. sexta Apn2) containing two hydrophobic regions. The NH2-terminal hydrophobic region corresponds to a secretory signal sequence and the COOH-terminal hydrophobic region is typical of glycosylphosphatidylinositol (glycosyl-PtdIns)-anchored proteins. Low-stringency hybridization of the P. xylostella midgut cDNA library with M. sexta apn2 probes enabled the isolation of a 3118-bp sequence with an ORF encoding a 946-residue preproprotein. This aminopeptidase N (P. xylostella Apn1) displays 61% amino acid identity to M. sexta Apn2 and contains a COOH-terminal signal peptide for glycosyl-PtdIns anchor addition. Both M. sexta Apn2 and P. xylostella Apn1 contain four Cys residues, which are highly conserved among eukaryotic aminopeptidase N molecules. Treatment of Sf9 cells expressing the P. xylostella apn1 gene with PtdIns-specific phospholipase C demonstrated that P. xylostella Apn1 is attached to the insect cell membrane by a glycosyl-PtdIns anchor.

Amino Acid Sequence↗

PubMed1994

Localization of aminopeptidase N and dipeptidyl peptidase IV in pig striatum and in neuronal and glial cell cultures.

The subcellular distribution of the plasma membrane ectoenzymes, aminopeptidase N (aminopeptidase M) and dipeptidyl peptidase IV, has been examined by fractionating homogenates of porcine striata by a discontinuous Percoll gradient centrifugation procedure which distinguishes fractions containing pre- and post-synaptic elements. The two enzymes showed different distributions--dipeptidyl peptidase IV did not show a significant pre-synaptic location, whereas aminopeptidase N was present on both pre- and post-synaptic fractions. Immunofluorescent staining on mixed and neuron-enriched primary cultures of pig striatal tissue using affinity purified antibodies to the aminopeptidase and to the dipeptidyl peptidase revealed the ectoenzymes on distinct populations of cells. The astrocytic identity of the aminopeptidase N-staining cells was established by correlation with immunostaining for glial fibrillary acidic protein and for vimentin by confocal microscopy. Ultracryosections of striatum immunostained with gold-labelled immunoglobulins of differing diameters demonstrated aminopeptidase N on pericytes and confirmed its location on endothelial and astrocytic glial cells. Thus, several independent approaches indicated that aminopeptidase N, in addition to being present on endothelial and synaptic membranes, is found on astrocytes and pericytes in the perivascular neuropil, whereas dipeptidyl peptidase IV is less widely distributed on microvessels and appears not to have a synaptosomal location.

Aminopeptidases↗

PubMed2003

Purification and characterization of an immunogenic aminopeptidase of Brucella melitensis.

An immunogenic aminopeptidase was purified from Brucella melitensis strain VTRM1. The purification procedure consisted of ammonium sulfate fractionation and three chromatographic steps. This procedure resulted in a yield of 29% and a 144-fold increase in specific activity. The aminopeptidase appeared to be a monomeric enzyme with a molecular mass of 96 kDa and an isoelectric point of 4.8. Its activity was optimal at pH 7.0 at 40 degrees C. The enzyme was strongly inhibited by EDTA, 1,10-phenathroline, and divalent cations (Zn(2+) and Hg(2+)), suggesting that this protein was a metalloaminopeptidase. The enzyme showed preference for alanine at the N termini of aminoacyl derivatives. The K(m) values for L-alanine-p-nitroanilide (Ala-pNA) and Lys-pNA were 0.35 and 0.18 mM, respectively. The N-terminal sequence of aminopeptidase was used for a homologous search in the genomes of B. melitensis 16M and Brucella suis 1330. The analysis revealed an exact match of the probe sequence (36 bp) with an open reading frame of 2,652 bp encoding a protein predicted to be alanyl aminopeptidase (aminopeptidase N). Collectively, these data suggest designation of the B. melitensis enzyme as an aminopeptidase N. The aminopeptidase was recognized by sera from patients with acute and chronic brucellosis, suggesting that the enzyme may have important diagnostic implications.

Amino Acid Sequence↗

PubMed2006

Brain aminopeptidases and hypertension.

The brain aminopeptidases that participate in the enzymatic cascade of the renin-angiotensin system play a major role in blood pressure (BP) control, and their study offers new perspectives for the understanding of central BP control and the treatment of hypertension. In this system, angiotensin II is converted to angiotensin III (Ang III) by glutamyl aminopeptidase (GluAP) and Ang III is further metabolised to angiotensin IV by alanyl aminopeptidase or arginine-aminopeptidase. It is now clear that Ang III is the key active form of the central angiotensins, exerting tonic stimulatory control over BP. Therefore, the development of GluAP inhibitors as potential antihypertensive agents offers new perspectives for therapy. Brain aspartyl aminopeptidase, which converts angiotensin I to angiotensin 2-10, is also a possible target for antihypertensive therapy because of its potential role in BP control. Finally, since changes in BP levels, that paralleled changes in brain and plasma aminopeptidase activities, were observed after unilateral lesions of the nigrostriatal system, brain asymmetry, aminopeptidase activities and BP control appear to be related, resulting their interplay in an asymmetrical neuroendocrine response that differentially affect BP control. The study of this interaction may contribute to our understanding of how the brain controls BP.

Aminopeptidases↗

PubMed2000

Aminopeptidase PC from the hepatopancreas of the Kamchatka crab Paralithodes camtshatica.

Homogeneous aminopeptidase PC was isolated with yield 67% and purification degree 237 from the hepatopancreas of the Kamchatka crab Paralithodes camtshatica by ion-exchange chromatography on DEAE-Sepharose, hydrophobic chromatography on Phenyl-Sepharose, and gel-filtration on Sephadex G-150. The enzyme is a homodimer with a molecular mass 220 kD (110 x 2). Aminopeptidase PC has pI = 4.1. It hydrolyzes Leu-pNA optimally at pH 6.0 and at the optimum temperature 36-40 degrees C; in the presence of Ca2+ the enzyme is stable at pH 5.5-8.0. Aminopeptidase PC is activated by Ca2+, Mg2+, and Fe2+; it is completely inhibited by EDTA, o-phenanthroline, and bestatin. The enzyme contains four Zn atoms per molecule and is therefore a metalloaminopeptidase. The aminopeptidase PC can effectively cleave N-terminal Arg and Lys residues as well as Leu, Phe, and Met residues. Km and kcat values for hydrolysis of Leu-pNA were 0.075 mM and 0.19 sec-1 and for hydrolysis of Arg-pNA 0.078 mM and 0.48 sec-1, respectively. D-Amino acid residues cannot be cleaved. Thus, aminopeptidase PC of the Kamchatka crab has a mixed substrate specificity which is characteristic of some microbe aminopeptidases. Its N-terminal sequence ESVEIELPEGLSPLV is 46% coincident with that of yeast vacuolar aminopeptidase YSCA.

Amino Acid Sequence↗

PubMed1991

[Utility of the L-alanine-aminopeptidase test for differentiating the cell wall structure of bacteria].

Evaluation of a detection test for L-alanine-aminopeptidase enzyme (Bactident Aminopeptidase) for determining the structure of bacterial cell wall. In a total of 246 clinical isolates of aerobic, microaerophilic and anaerobic bacteria, we detect the presence or absence of L-alanine-aminopeptidase using commercial kits (Bactident Aminopeptidase, Merck Diagnostica). We also identify and further classified the 246 strains. In nearly all gram-negative bacteria L-alanine-aminopeptidase was found, with the exception of Campylobacter spp and gram-negative anaerobic bacilli. All gram-positive and gram-variable bacteria were negative for the L-alanine-aminopeptidase presence. The results suggest a good correlation between the presence or absence of L-alanine-aminopeptidase and Gram stain method.

Aminopeptidases↗

PubMed1978

Aminopeptidase activities on the surface of mammalian cells and their alterations associated with transformation.

Activities of various hydrolytic enzymes were determined in rat organ homogenates and on the surface of cells from various sources, i.e., tumor cell strains, primary cultured cells, normal cells, and their transformants. Alanine, leucine, methionine, phenylalanine, and glycyl-proline aminopeptidases and esterase showed relatively high activities in all these organs and cells. In the kidney homogenate the aminopeptidase A activity was higher in other organs; i.e., the aminopeptidase A activity was lower than that of aminopeptidase B. Normal cells derived from kidneys showed the kidney-type pattern of amino-peptidases A and B on the surface of cells, whereas tumor cells from various origins were of another organ type. When cultured mouse fibroblast strain C3H2K and rat fibroblast strain 3Y1 cells were transformed by SV40 or by a ts A mutant and maintained at permissive temperature, aminopeptidase A activity was drastically decreased, and the ratio of aminopeptidase A to aminopeptidase B was reduced to the levels of tumor cells. If the ts A mutant-transformed cells were grown at the restrictive temperature, the ratio approached that of normal cells. In normal cells, however, cultivation at high or low temperature did not cause any change of the activities.

Aminopeptidases↗

PubMed1989

Amino acid sequence deduced from a rat kidney cDNA suggests it encodes the Zn-peptidase aminopeptidase N.

We have isolated and characterized rat kidney cDNA clones encoding a 140-kDa glycoprotein that exhibits characteristics of a cell surface Zn-peptidase. Structural features predicted for this putative kidney Zn-peptidase (KZP) are most consistent with properties previously determined for the Zn-peptidase aminopeptidase N. The deduced amino acid sequence of rat KZP is almost identical to the NH2-terminal sequence of aminopeptidase N purified from rabbit. The overall amino acid composition predicted for rat KZP is remarkably similar to that previously determined for rabbit and pig aminopeptidase N. The predicted Mr of rat kidney KZP approximates the Mr of the unglycosylated form of aminopeptidase N. The topology predicted for KZP is identical to that observed for aminopeptidase N: a short cytoplasmic domain at the NH2 terminus immediately precedes an uncleaved signal/anchor domain; a stalk region connects this membrane anchor to the extracellular, hydrophilic bulk of the protein containing catalytic sites required for Zn-peptidase activity. In addition, mRNA encoding KZP is present in tissues known to exhibit aminopeptidase N activity. Taken together with the observation that only a single gene homologous to KZP DNA is present in the rat and human genomes, these results suggest that we have established the primary structure of rat kidney aminopeptidase N.

Amino Acid Sequence↗

PubMed1983

Content and turnover of rat intestinal microvillus membrane aminopeptidase. Effect of methylprednisolone.

The reasons for the difference in aminopeptidase activity between jejunum and ileum and the changes in enzyme activity after corticosteroid administration were investigated in rat small intestine. The aminopeptidase activity of microvillus membrane in jejunum was higher than in ileum. Methylprednisolone treatment enhanced the enzyme activity in both regions. The amount of enzyme as measured by a competitive radioimmunoassay was higher in jejunum than in ileum, and methylprednisolone administration increased the content of aminopeptidase in both regions. The kinetic parameters of aminopeptidase from both regions showed no difference and were not affected by methylprednisolone treatment. The maximum incorporation of [3H]glucosamine into immunoprecipitable aminopeptidase in jejunum was greater than in ileum, and methylprednisolone administration increased the incorporation in both regions. The degradation rate of aminopeptidase in jejunum was higher than in ileum, and methylprednisolone administration had no effect on the rate of degradation in either region. It was concluded that jejunum has a greater content of aminopeptidase than ileum due to a higher rate of enzyme synthesis, and that methylprednisolone administration increases the enzyme content by increasing the synthetic rate.

Aminopeptidases↗