Regulation of angiotensin I-converting enzyme activity in serially cultivated bovine endothelial cells

Angiotensin I-converting enzyme (ACE) activity was measured in lysates of cloned and uncloned cultures of bovine fetal aortic endothelial cells. The expression of ACE activity in these cells was complex, and influenced by subcultivation, cell density, serum, cumulative population doublings, and clonal heterogeneity. The ACE specific activity at any point in the in vitro lifespan was determined, at least in part, by interaction of these culture variables. After subcultivation to subconfluent densities, cellular ACE specific activity decreased markedly and did not reach detectable levels until cells attained confluent densities. The use of different suppliers' lots of serum in the growth medium resulted in different cellular ACE specific activities. The ACE specific activity decreased as cultures were serially subcultivated, but remained detectable throughout the lifespan, suggesting a linkage between the proliferative history of an endothelial cell and its remaining capacity to express ACE. Increased ACE activity was observed when cells at the end of their lifespan were cultured at high densities. Cloned strains behaved similarly to the uncloned parent culture, except that they exhibited a wide range of ACE specific activities.     

Regulation of angiotensin I-converting enzyme in cultured bovine bronchial epithelial cells

The purpose of this study was to determine whether angiotensin I-converting enzyme (ACE) is present in cultured bovine bronchial epithelial cells (BBECs) and whether its activity can be modulated. We found that extracts of confluent monolayers of cultured BBECs degraded [glycine-1-¹⁴C]hippuryl-L -histidyl-L -leucine at a rate of 843 ± 66 pmol/hr/mg protein (mean ± SEM, n = 5). In addition, we found that the enzyme was shed into the culture medium. ACE activity in BBECs was inhibited by three selective, but structurally different, ACE inhibitors (captopril, quinapril, and cisalaprilat) with an IC₅₀ of approximately 2 nM. Increasing chloride concentration in the assay buffer resulted in an increase in BBECs ACE activity of 63%. Enzyme activity was also modulated by the presence of zinc cation in the assay buffer. Addition of dexamethasone to the culture medium was associated with a significant increase in BBECs ACE activity (P < 0.05), which was inhibited by the steroid receptor antagonist RU 38486. Western blot analysis of BBECs, tracheal and bronchial mucosal strips utilizing a cross-reacting rabbit anti-mouse ACE antibody, showed a faint 175 kDa band and additional strong 52 kDa and 47 kDa band. The mechanism of generation of the low M.W. bands is unknown. Our data indicate the presence of ACE in cultured BBECs and that enzyme activity can be modulated.     

Induction by fibroblast growth factor of angiotensin converting enzyme in vascular endothelial cells in vitro

Induction of vascular endothelial cells with pituitary fibroblast growth factor (FGF) provoked an increase in angiotensin converting enzyme activity. The stimulatory effect of FGF on ACE activity was dose-dependent (ED50 = 1.0 ng/ml). Our results suggest a possible role for pituitary FGF in regulation of ACE production in vascular endothelial cells.     

Purification of human serum angiotensin I-converting enzyme by affinity chromatography

A relatively simple procedure is described for purifying human serum angiotensin-converting enzyme. The enzyme was purified 130,000-fold to electrophoretic homogeneity using affinity chromatography as the principal purification step. The ligand was an immobilized competitive inhibitor, d-cysteinyl-l-proline. A six-carbon spacer arm was satisfactory for trapping the enzyme; 80% of the bound enzyme was eluted with 3 m urea-1.0 m NaCl-0.1 m Tris, pH 8.3. The specific activity was 39 units/mg protein and the molecular weight (155,000), isoelectric point (4.7), kinetic properties, and the effect of various inhibitors are in agreement with published reports.     

A high-throughput fluorimetric assay for angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE) assays are commonly used for measuring enzymatic activity in clinical and biological samples. The fluorimetric procedure described is sensitive, rapid and involves unsophisticated procedures and inexpensive reagents. It uses the substrate hippuryl-L-histidyl-L-leucine, and the fluorescent adduct of the enzyme-catalyzed product L-histidyl-L-leucine is quantified fluorimetrically. This assay has been adapted for a 96-well plate format that produces comparable data to previously described assays and has the advantage of greater efficiency with respect to both time and reagents. The protocol can be used for routine purposes or for more detailed kinetic analyses. The apparent Km and kcat values for purified testis ACE determined from a double reciprocal plot were 3.0 mM and 195.7 s(-1), respectively. The protocol can be completed within 4 h.     

Restriction of the in vitro formation of angiotensin II by leucinyl-arginyl-tryptophan, a novel peptide with potent angiotensin I-converting enzyme inhibitory activity

Leucinyl-arginyl-tryptophan (LRW) is a new peptide inhibitor of the angiotensin converting enzyme (ACE) that was previously predicted through quantitative structure-activity relationship modeling. LRW inhibited ACE activity in a competitive manner with a higher K(m) value in the presence of the peptide, and the in vitro formation of angiotensin II by ACE was significantly reduced in the presence of LRW up to 60 min of incubation time.     

Purification of angiotensin I-converting enzyme from human lung.

Angiotensin I-converting enzyme (peptidyl dipeptide hydrolase, EC 3.4.15.1) was solubilized from the membrane fraction of human lung using trypsin treatment and purfied using columns of DE 52-cellulose, hydroxyapatite and Sephadex G-200. The purified enzyme was shown to convert angiotensin I to angiotensin II and also to inactivate bradykinin. The specific activity of the enzyme was 9.5 units/mg protein for Hippuryl-His-Leu-OH and 0.665 mumol/min per mg protein for angiotensin I. The enzymic activity obtained after trypsin treatment (1 mg/200 mg protein) for 2 h could be divided into three components: (i) an enzyme of molecular weight 290 000 (peak I), (ii) an enzyme of molecular weight 180 000 (peak II) and (iii) an enzyme of molecular weight 98 000 (peak III), by columns of DE 52-cellulose and Sephadex G-200. Km values of peak I, II and III fraction for Hippuryl-His-Leu-OH were identical at 1.1 mM. pH optimum of the enzyme was 8.3 for Hippuryl-His-Leu-OH.     

Dipeptide-hydroxamates are good inhibitors of the angiotensin I-converting enzyme

The inhibition constants (Ki) and modes of inhibition have been determined for a series of dipeptide-hydroxamate compounds with bovine lung parenchyma angiotensin I-converting enzyme (peptidyldipeptide carboxy-hydrolase, E.C. 3.4. 15.1). The hydroxamido function was borne by aspartic, glutamic, or aminoadipic acid and extended by 2, 3 or 4 bond lengths from the proline amide bond. L-glu(NHOH)-L-pro (Ki = 3.4 microM) and D,L-aminoadipicyl (NHOH)-L-pro (Ki = 1.2 microM) were the best competitive inhibitors of the hydrolysis of benzoyl-gly-his-gly but were not effective as affinity ligands for purification of the enzyme.     

Tissue angiotensin I-converting enzyme activity in spontaneously hypertensive hamsters.

The purpose of this study was to measure angiotensin I-converting activity in heart, kidney, lung and cheek pouch tissue homogenates of spontaneously hypertensive and normotensive hamsters. We also determined inhibitor sensitivity and the effects of chloride anion concentration on kidney angiotensin I-converting activity in these animals. We found no significant differences in angiotensin I-converting activity between hypertensive and normotensive hamsters in all tissues tested. Inhibitor sensitivity of kidney angiotensin I-converting activity with captopril and lisonopril was similar in both groups. Finally, kidney angiotensin I-converting activity increased significantly in both groups as chloride anion concentration in the assay buffer increased. Substituting chloride anion for citrate abrogated the increase in angiotensin I-converting enzyme activity.     

Human angiotensin I-converting enzyme gene and endurance performance.

Human physical performance is strongly influenced by genetic factors. A variation in the structure of the human angiotensin I-converting enzyme (ACE) gene has been reported in which the insertion (I) variant is associated with lower ACE levels than the deletion (D) gene. We have previously reported that the I variant was associated with improved endurance performance in high-altitude mountaineers and British Army recruits. We now examine this genotype distribution in 91 British Olympic-standard runners (79 Caucasians). DNA was extracted from the buccal cells contained in 10 ml of saline mouthwash donated by the subjects, and the I and D variants of the ACE gene were identified by PCR amplification of the polymorphic region. There was an increasing frequency of the I allele with distance run [0.35, 0.53, and 0.62 for /=5,000 m (n = 34), respectively; P = 0.009 for linear trend]. Among 404 Olympic-standard athletes from 19 other mixed sporting disciplines (in which endurance performance was not necessarily a key factor), the I allele did not differ significantly from that found in control subjects: 0.50 vs. 0.49 (P = 0.526). These results support a positive association of the I allele with elite endurance performance.     

Interaction of angiotensin I-converting enzyme with two potent tricyclic inhibitors

Inhibition of rabbit lung angiotensin I-converting enzyme was studied with two inhibitors that combined tricyclic mimics of a substrate C-terminal dipeptide recognition unit with a 4-phenylbutanoic acid fragment. The overall inhibition constant for [4S-[4 alpha, 7 alpha(R*),12b beta]]-7-[S-(1-carboxy-3-phenylpropyl) amino]-1,2,3,4,6,7,8,12b-octahydro-6-oxopyrido[2,1-a] [2] benzazepine-4-carboxylic acid (MDL 27,088) was approximately 4 pM, whereas that for [4R-[4 alpha, 7 alpha(S*), 12b beta]]-7-[S-(1-carboxy-3-phenylpropyl)amino]-3,4,6,7,8, 12b-hexahydro-6-oxo-1H-[1,4]thiazino[3,4-a] [2]benzazepine-4-carboxylic acid (MDL 27,788) was estimated to be 46 pM. The formation of an initial complex of target enzyme and MDL 27,088 and its slower isomerization to a second complex were characterized kinetically. Both compounds appear to be among the most potent inhibitors known for this enzyme.     

Peptide inhibitors of angiotensin I-converting enzyme in digests of gelatin by bacterial collagenase.

Peptide inhibitors of angiotensin I-converting enzyme (peptidyldipeptide hydrolase, EC 3.4.15.1) were produced by digesting gelatin with bacterial collagenase. The inhibitors were isolated from the digests with a combination of alcohol fractionation, treatment with Amberlite CG-50 column, gel filtration through Sephadex G-25, and Dowex 50 column and paper chromatography. Nine peptide fractions were purified to apparent homogeneity judging by thin-layer and ion-exchange column chromatography, and amino acid composition. Amino acid sequences of the peptides were determined: 2 were found to be mixtures of peptides and the sequence of another was only partially determined. Six of the peptides were potent inhibitors of the converting enzyme, while the other three were less active. 6 peptides were substrates for the enzyme. The enzyme released a dipeptide, Ala-Hyp from one peptide and was strongly inhibited by this dipeptide. The remainder of the parent peptides was a less effective inhibitor.     

Possible involvement of angiotensin I-converting enzyme in the inactivation of bradykinin by intact macrophages

As intact macrophages inactivated bradykinin, the subcellular localization of the bradykinin-inactivating activity was studied using guinea-pig macrophages. The bradykinin-inactivating activity was found to be present in membrane and cytosol fractions but not in granular and nuclear fractions. The bradykinin-inactivating activity of the membrane fraction was inhibited by captopril, a specific inhibitor of angiotensin I-converting enzyme, whereas that of the cytosol fraction was hardly inhibited by various proteinase inhibitors used. Angiotensin I-converting enzyme activity was located predominantly in the membrane fraction and its activity was inhibited by captopril. Angiotensin I-converting enzyme activity measured with a synthetic substrate was competitively inhibited by bradykinin, suggesting that bradykinin is a possible substrate for macrophage angiotensin I-converting enzyme. When macrophages were modified chemically by diazotized sulfanilic acid, a poorly permeant reagent, both the bradykinin-inactivating activity and the angiotensin I-converting enzyme activity of macrophages decreased significantly without any inhibition of the cytosol bradykinin-inactivating activity. These findings seem to suggest that the angiotensin I-converting enzyme would be responsible for the inactivation of bradykinin in intact macrophages.     

Functional study of the germinal angiotensin I-converting enzyme promoter.

Polymerase chain amplification experiments indicate that the germinal specific promoter of the angiotensin I-converting enzyme (ACE) is completely extinguished in somatic tissues. Despite this very strict specificity of expression, the germinal ACE promoter is active in transient transfection experiments in two somatic cell lines and one cell line of germinal origin. The analysis of the promoter shows the existence two regulatory elements within the first 350 bp: a proximal positive element and a distal negative element.     

Stereospecificity of peptidyl dipeptide hydrolase (angiotensin I-converting enzyme).

The stereospecificity of peptidyl dipeptide hydrolase [EC 3.4.15.1] was investigated. Six free and N-blocked alanyl peptides containing D-alanine were synthesized and tested as substrates. Their susceptibilities were determined by measuring Ala-Ala release by cation exchange column chromatography. Their Michaelis constants, Km values, and velocity maxima, Vmax values, were also determined. The enzyme showed high stereospecificity for an amino acyl residue in position 3 from C-terminus: it had an absolute requirement for the alanyl residue of the L-configuration in this position. An alanyl residue of the L-configuration in position 1 or 2 increased, but was not essential for activity. The enzyme showed little stereospecificity for an alanyl residue in position 4 from the C-terminus.     

Defining the boundaries of the testis angiotensin I-converting enzyme ectodomain

Numerous cytokines, receptors, and ectoenzymes, including angiotensin I-converting enzyme (ACE), are shed from the cell surface by limited proteolysis at the juxtamembrane stalk region. The membrane-proximal C domain of ACE has been implicated in sheddase-substrate recognition. We mapped the functional boundaries of the testis ACE ectodomain (identical to the C domain of somatic ACE) by progressive deletions from the N- and C-termini and analysing the effects on catalytic activity, stability, and shedding in transfected cells. We found that deletions extending beyond Leu37 at the N-terminus and Trp616 at the C-terminus abolished catalytic activity and shedding, either by disturbing the ectodomain conformation or by inhibiting maturation and surface expression. Based on these data and on sequence alignments, we propose that the boundaries of the ACE ectodomain are Asp40 at the N-terminus and Gly615 at the C-terminus.     

Structural and biological roles of glycosylations in pulmonary angiotensin I-converting enzyme

We enzymatically deglycosylated pig lung angiotensin I-convertingenzyme (ACE) to study the involvement of its glycanic chainsin its physicochemical and catalytic properties. The effectsof endoglycosidases F₂ and H, and of N-glycanase were assessedby ACE mobility in SDS-PAGE. N-Glycanase only was completelyeffective with or without previous denaturation, leading toa shift in ACE M_r from 172 to 135 kDa; endoglycosidase F₂ producedthe same shift but only without previous denaturation. DeglycosylatedACE had the same kcat as native ACE for the substrate hippuryl-histidyl-leucine,and an identical Stokes radius as measured by size-exclusionhigh performance liquid chromatography. Neuraminidase had noeffect on ACE Stokes radius but slightly decreased its kcatwhich could be related to variations in ionization of the activesite. The isoelectric point of ACE, as, determined by isoelectricfocusing, increased from 4.5–4.8 to 5.0–5.3 aftereither endoglycosidase F₂ or neuraminidase digestion, but stillwith microheterogeneities which thus did not seem to be relatedto ACE glycans. Deglycosylated ACE did not bind onto agaroselectinsin contrast to native ACE which bound strongly to concanavalinA showing interactions involving oligomannosidic or biantennaryand sialylated N-acetyl-lactosaminic isoglycans. Finally, tunicamycin,an inhibitor of N-glycosylation, did not modify ACE secretionby endothelial cells. Thus, ACE glycans have no drastic effectson structural and biological properties of the protein, butthey may have a functional role on intracellular targeting ofboth secreted and membrane-bound ACE isoforms, also for theprotection of the soluble plasma form against hepatic lectinsand the maintenance of its hydrosolubility. converting enzyme (peptidyldipeptidase EC.3.4.15.1) endothelium glycosidases lectins