Rabbit pulmonary angiotensin-converting enzyme: the NH2-terminal fragment with enzymatic activity and its formation from the native enzyme by NH4OH treatment

Angiotensin I-converting enzyme Gln1069Arg mutation impairs trafficking to the cell surface resulting in selective denaturation of the C-domain

Background

Angiotensin-converting enzyme (ACE; Kininase II; CD143) hydrolyzes small peptides such as angiotensin I, bradykinin, substance P, LH-RH and several others and thus plays a key role in blood pressure regulation and vascular remodeling. Complete absence of ACE in humans leads to renal tubular dysgenesis (RTD), a severe disorder of renal tubule development characterized by persistent fetal anuria and perinatal death.

Methodology/Principal Findings

Patient with RTD in Lisbon, Portugal, maintained by peritoneal dialysis since birth, was found to have a homozygous substitution of Arg for Glu at position 1069 in the C-terminal domain of ACE (Q1069R) resulting in absence of plasma ACE activity; both parents and a brother who are heterozygous carriers of this mutation had exactly half-normal plasma ACE activity compared to healthy individuals. We hypothesized that the Q1069R substitution impaired ACE trafficking to the cell surface and led to accumulation of catalytically inactive ACE in the cell cytoplasm. CHO cells expressing wild-type (WT) vs. Q1069R-ACE demonstrated the mutant accumulates intracellularly and also that it is significantly degraded by intracellular proteases. Q1069R-ACE retained catalytic and immunological characteristics of WT-ACE N domain whereas it had 10–20% of the nativity of the WT-ACE C domain. A combination of chemical (sodium butyrate) or pharmacological (ACE inhibitor) chaperones with proteasome inhibitors (MG 132 or bortezomib) significantly restored trafficking of Q1069R-ACE to the cell surface and increased ACE activity in the cell culture media 4-fold.

Conclusions/Significance

Homozygous Q1069R substitution results in an ACE trafficking and processing defect which can be rescued, at least in cell culture, by a combination of chaperones and proteasome inhibitors. Further studies are required to determine whether similar treatment of individuals with this ACE mutation would provide therapeutic benefits such as concentration of primary urine.

Expression and localization of N-domain ANG I-converting enzymes in mesangial cells in culture from spontaneously hypertensive rats

The angiotensin-converting enzyme (ACE) profile in urine of hypertensive patients and spontaneously hypertensive rats (SHR; 90- and 65-kDa N-domain ACEs) is different from that of healthy subjects and Wistar rats (190 and 65 kDa). In addition, four ACE isoforms were purified from mesangial cells (MC) of Wistar rats in the intracellular compartment (130 and 68 kDa) and as secreted forms (130 and 60 kDa). We decided to characterize ACE forms from SHR MC in culture. Analysis of the ACE gene showed that SHR MC are able to express ACE mRNA. The concentrated medium and cell homogenate were separately purified by gel filtration and then subjected to lisinopril-Sepharose chromatography. The molecular masses of purified enzymes, 90 kDa for ACEm1A and 65 kDa for ACEm2A (secreted enzymes) and 90 kDa for ACEInth1A and 65 kDa for ACEInth2A (intracellular), were different from those of Wistar MC. The purified enzymes are Cl−dependent, inhibited by enalaprilat and captopril, and able to hydrolyze AcSDKP. Immunofluorescence and cell fractionation followed by Western blotting showed predominant immunoreaction of the 9B9 antiserum for N-domain ACE in the nuclei. The N-domain ACE was localized in the glomerulus from Wistar rats and SHR. ANG II and ANG-(1–7) were localized in the cell cytoplasm and nuclei. The 90-kDa N-domain ACE, described recently as a possible genetic marker of hypertension, was found inside the cell nuclei of SHR MC colocalized with ANG II and ANG-(1–7). The presence of ANG II in the cell nuclei could suggest an important role for this peptide in the transcription of new genes.

N-domain angiotensin I-converting enzyme with 80 kDa as a possible genetic marker of hypertension

We have previously described angiotensin I-converting enzyme (ACE) forms in urine of normotensive (190 and 65 kDa) and hypertensive patients (90 and 65 kDa, N-domain ACEs). Based on the results described above, experimental and genetic models of hypertension were investigated to distinguish hemodynamic and genetic influence on the generation of ACE profile in urine: Wistar-Kyoto and Brown Norway rats (WKY and BN), spontaneously and stroke-prone spontaneously hypertensive rats (SHR and SHR-SP), one kidney/one clip rats (1K1C), deoxycorticosterone acetate (DOCA) salt-treated and untreated rats, and enalapril-treated SHR (SHRen). Two peaks with ACE activity were separated from the urine of WKY and BN rats submitted to an AcA-44 column, WK-1/BN-1 (190 kDa), and WK-2/BN-2 (65 kDa), as described for urine of normotensive subjects. The same results were obtained for urine of 1K1C and DOCA salt-treated and untreated rats, analyzed to evaluate the influence of hemodynamic factors in the ACE profile in urine. The urine from SHR, SHR-SP, and SHRen presented 80 (S-1, SP-1, Sen-1) and 65 (S-2, SP-2, Sen-2) kDa ACE forms, differing from the urine profile of normotensive rats, but similar to that described for hypertensive patients. The presence of 80 kDa ACE in urine of SHR, SHR-SP, and SHRen and its absence in urine of experimental hypertensive rats (1K1C and DOCA salt) support the hypothesis that this enzyme could be a possible genetic marker of hypertension. Taken together, our results provide evidence that ACE forms with 90/80 kDa isolated from the urine of hypertensive subjects and genetic hypertensive animals behaves as a possible genetic marker of hypertension and not as a marker of high blood pressure.

Angiotensin converting enzymes from human urine of mild hypertensive untreated patients resemble the N-terminal fragment of human angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE) activity was analyzed in human urine collected from mild hypertensive untreated patients. DEAE-cellulose chromatography using linear gradient elution revealed two forms of angiotensin I-converting enzyme, eluted in the conductivity of 0.75 and 1.25 mS. The fractions of each conductivity were pooled and submitted to direct gel filtration in an AcA-34 column, and the apparent molecular weights of urinary ACEs were estimated as 90 kDa (for ACE eluted in 0.75 mS) and 65 kDa (for ACE eluted in 1.25 mS). Both enzymes have a K(i) of the order of 10(-7) M for the specific inhibitors studied, and are able to hydrolyze luteinizing hormone-releasing hormone and N-acetyl-Ser-Asp-Lys-Pro as described for N-domain ACE. By Western blot analysis, both peaks were recognized by ACE-specific antibody Y4, confirming the molecular weight already described. A plate precipitation assay using monoclonal antibodies to the N-domain of ACE showed that both forms of ACE binds with all monoclonal antibodies to the active N-domain ACE, suggesting that these forms of human urine ACEs resemble the N-fragment of ACE. The HP2 ACE (65 kDa) is similar to low molecular weight (LMW) ACE from normal subjects, and the HP2 ACE (90 kDa) is different from high molecular weight (190 kDa) and LMW (65 kDa) normal ACEs. The 90 kDa ACE could have an important role in development of hypertension. It will be fundamental to elucidate the molecular mechanism responsible for the genesis of this isoform.

Some molecular and inhibitory specifications of a dipeptidyl carboxypeptidase from the polychaete Neanthes virens resembling angiotensin I converting enzyme

Dipeptidyl carboxypeptidase (DCP) from the polychaete Neanthes virens, resembling mammalian angiotensin I converting enzyme (ACE), was studied to discover some of its molecular and inhibitory properties, as the first evidence of these in a marine invertebrate. Amino acid and carbohydrate contents were analyzed. The N-terminal amino acid sequence of N. virens DCP was (NH2)D-E-E-A-G-R-Q-W-L-A-E-Y-D-L-R-N-Q-T-V-L-. Peptide maps of N. virens DCP from lysyl endopeptidase digestion were different from rabbit p-ACE. The far-ultraviolet circular dichroic spectra of N. virens DCP indicated that the secondary structure of this enzyme seemed to be an alpha-helical structure and was similar to that of rabbit p-ACE, but the near-ultraviolet circular dichroic spectra of N. virens DCP indicated that the aromatic amino acid residue circumambience of this enzyme was different from rabbit p-ACE. The effects of several reagents for chemical modification of amino acids on the activity of N. virens DCP were tested. Arg, Tyr, Glu, and/or Asp, His, Trp, and Met caused loss of the activity. In addition, the IC50 and Ki values for a well-known ACE inhibitor, Val-Tyr, which was a competitive inhibitor of N. virens DCP, were 263 and 20 microM, respectively. These results suggested that N. virens DCP is different from mammalian ACE in the molecular and inhibitory properties, although the same substrate specificity was demonstrated in a previous paper.

Angiotensin I-converting enzyme isoforms (high and low molecular weight) in urine of premature and full-term infants

Angiotensin I-converting enzyme (ACE) isoforms in urine from healthy and mildly hypertensive untreated patients have been described in the literature. Healthy subjects have high- and low-molecular-weight ACEs (170 and 65 kDa), whereas mildly hypertensive untreated patients have only low-molecular-weight ACEs (90 and 65 kDa), both of which resemble ACE from the N-terminal domain. Previous studies have shown that ACE is regulated during development, and renal tubules of premature human infants are not completely mature, given that nephrogenesis is not complete until the 36th week of gestation. The aim of the present study was to purify and characterize ACE isoforms from urine of premature and full-term infants and to detect the presence of the N-domain form of ACE during prenatal development. Urine from premature and full-term infants was concentrated in an Amicon concentrator, dialyzed in the same equipment against 50 mmol/L Tris-HCl buffer (pH 8.0) that contained 150 mmol/L NaCl, and submitted to gel filtration on an AcA-34 column equilibrated with the buffer described above. Two peaks (P1 and P2 for premature infants; TP1 and TP2 for full-term infants) with ACE activity on hippuryl-His-Leu (K(m), 3 mmol/L) were detected. All enzymes were Cl(-) dependent and inhibited by captopril and EDTA. The peptides angiotensin-(1-7) and N-acetyl-Ser-Asp-Lys-Pro, described as specific for N-domain ACE, were hydrolyzed by P2 and TP2, which suggests that both enzymes are N-domain ACE. In premature infants, P1 activity with hippuryl-His-Leu was 12-fold lower than P2 activity, but in full-term infants, the difference between TP1 and TP2 was 1.6-fold. Chromatography profiles of urine from premature infants were analyzed on days 1, 3, 7, 14, 21, and 30 after birth. The P1 of ACE was detected around the 21st and 30th days, whereas P2 was detected from day 1. These results suggest that ACE activity is related to renal development and that N-domain ACE as well as full-length ACE is present in urine from premature infants. This may indicate that healthy subjects produce and secrete the N-domain form of ACE even before term development.

Angiotensin converting-like enzymes from urine of untreated renovascular hypertensive and normal patients: purification and characterization

Angiotensin converting-like enzymes (ACE) were isolated from urine of normal (P0N, P1N and P2N) and untreated renovascular hypertensive (P0, P1 and P2) patients. The urine were submitted to ion exchange chromatography. Enzymes P0 and P0N were eluted with the equilibrium buffer (0.02 M Tris-HCl, pH 7.0), while P1, P1N, P2 and P2N with ionic strength linear gradient of 0.02-0.5 M Tris-HCl, pH 7.0 in 0.7 mS and P2 and P2N in 1.2 mS conductance. The active fractions were submitted to gel filtration in Sephadex G-150, equilibrated and performed with 0.05 M Tris-HCl/0.15 M NaCl buffer, pH 8.0. All enzymes were homogeneous when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) (molecular mass: P0, P2 and P2N about 60 kDa; P1, 95 kDa and P21N 170 kDa). The enzymes were recognized by Y1 polyclonal antibody raised against human renal ACE. The K(M) values were in millimolar order for hippuryl-L-His-Leu (HHL) while for benzyloxycarbonyl-Phe-L-His-Leu (ZFHL) they were in 10(-4) M order. The enzymes were able to hydrolyze angiotensin I (AI) (P0 and P0N about 25%, P1 and P1N about 70%, P2 100% and P2N 66%) and bradykinin (BK) (P0N 22%, P1N 81%, P2N 62%, P0 and P1 50% and P2 35%), and their activities were inhibited by captopril.

Purification and characterization of angiotensin I-converting enzymes from mesangial cells in culture

OBJECTIVE

Previous analysis of the angiotensin I-converting enzyme (ACE) gene in this laboratory showed that primary mesangial cells in culture are able to express ACE mRNA. Moreover, ACE is produced as an ectoenzyme and as a secreted form of the enzyme, indicating a potential effect of local angiotensin II production on glomerular microcirculation. The aim of this study was to purify and characterize the secreted and intracellular ACE forms from mesangial cells in culture.

METHODS AND RESULTS

Medium from Wistar rats mesangial cells was collected (third passage), incubated for 20 h with RPMI without fetal bovine serum and concentrated 29 times in an Amicon concentrator. The concentrated medium was submitted to gel filtration on an AcA-34 column and two peaks (ACE1, mol. wt 130 000 and ACE2, 60000) with ACE on activity Hippuryl-His-Leu and Z-Phe-His-Leu were separated. The mesangial cells were collected and ACE enzyme was extracted using Triton X-114, followed by centrifugation and concentration. The supernatant was submitted to the same chromatography as described above and two peaks with ACE activity (ACEInt1, mol. wt 130000 and ACEInt2, 68000) were separated. The purified ACE were inhibited by enalaprilat and captopril, two potent competitive inhibitors of ACE and by EDTA, using Hippuryl-His-Leu as a substrate. The Km values were 2 mM for ACE1 and ACE2 and 3 mM for ACEInt1 and ACEInt2. The enzymes ACE1 and ACE2 presented an optimum pH of 8.0 and ACEInt1 and ACEInt2 an optimum pH of 7.5.

CONCLUSION

The activities of full-length wild-type and N-domain ACE were characterized by the ratio of the hydrolysis of Z-Phe-His-Leu/Hippuryl-His-Leu, which was 1 and 4, respectively. The ratios found for ACE1, ACE2, ACEInt1 and ACEInt2 in the present study were similar to those described above, suggesting that mesangial cells, besides showing the presence of intracellular ACE, are able to secret both full-length wild-type ACE and N-domain ACE. Thus, they may potentially have an effect, not only on bradykinin and angiotensin I (ACE wild-type), but also on substance P, luteinizing hormone-releasing hormone and Met-enkephalin to interfere with glomerular haemodynamics and with the renal microcirculation.

Limited proteolysis of human kidney angiotensin-converting enzyme and generation of catalytically active N- and C-terminal domains

The somatic form of angiotensin converting enzyme is a class I ectoenzyme that is bound to the surface of endothelial calls. It consists of two homologous, catalytic domains of approximately 600 residues each; a juxtamembrane "stalk" region; a transmembrane, hydrophobic sequence; and a 30 residue, C-terminal cytosolic domain. We have used limited proteolysis to probe the structural and functional properties of the enzyme. Endoproteinase Asp-N cleaves both the Thr615-Asp616 and the Leu1219-Asp1220 peptide bonds to generate the two catalytic domains which were isolated by a combination of immunoaffinity and lisinopril Sepharose affinity chromatography. The enzymatic characteristics of the N and C fragments were examined with angiotensin I, hippuryl-His-Leu, and luteinizing hormone-releasing hormone and indicate that both fragments contain catalytically active sites that retain their individual functional integrity.

The Mg(2+)-ATPase of rabbit skeletal-muscle transverse tubule is a highly glycosylated multiple-subunit enzyme

The Mg(2+)-ATPase present in rabbit skeletal-muscle transverse tubules is an integral membrane enzyme which has been solubilized and purified previously in this laboratory [Kirley (1988) J. Biol. Chem. 263, 12682-12689]. The present study indicates that, in addition to the approx. 100 kDa protein (distinct from the sarcoplasmic-reticulum Ca(2+)-ATPase) seen previously to co-purify with the Mg(2+)-ATPase activity, there are also proteins having molecular masses of 160, 70 and 43 kDa. The 70 and 43 kDa glycosylated proteins (50 and 31 kDa after deglycosylation) are difficult to detect by SDS/PAGE before deglycosylation, owing to the broadness of the bands. Additional purification procedures, cross-linking studies and chemical and enzymic deglycosylation studies were undertaken to determine the structure and relationship of these proteins. Both the 97 and 160 kDa proteins were demonstrated to be N-glycosylated at multiple sites, the 97 kDa protein being reduced to a peptide core of 84 kDa and the 160 kDa protein to a peptide core of 131 kDa after deglycosylation. Although the Mg(2+)-ATPase activity is resistant to a number of chemical modification reagents, cross-linking inactivates the enzyme at low concentrations. This inactivation is accompanied by cross-linking of two 97 kDa molecules to one another, suggesting that the 97 kDa protein is involved in ATP hydrolysis. The existence of several proteins along with the inhibition of ATPase activity by cross-linking is consistent with the interpretation of the susceptibility of this enzyme to inactivation by most detergents as being due to the disruption of a protein complex of associated subunits by the inactivating detergents. The 160 kDa glycoprotein can be partially resolved from the Mg(2+)-ATPase activity, and is identified by its N-terminal amino acid sequence as angiotensin-converting enzyme.

Angiotensin converting enzyme: implications from molecular biology for its physiological functions

1. The two isozymes of human angiotensin converting enzyme (ACE; EC 3.4.15.1) have recently been cloned and sequenced. 2. The larger, endothelial isozyme has two highly similar internal domains each bearing a putative catalytic site. In contrast the smaller, testicular isozyme has a single catalytic site corresponding to the C-terminal domain of endothelial ACE and represents the ancestral, non-duplicated form of the gene. 3. Both isozymes are anchored in the plasma membrane by a single hydrophobic transmembrane polypeptide located near the C-terminus, and both are extensively N-glycosylated. 4. The testicular isozyme may also be O-glycosylated. 5. The soluble form of ACE in plasma, seminal fluid and other body fluids appears to be derived from the membrane-bound endothelial isozyme by a post-translational modification. 6. ACE has a complex substrate specificity with peptidyl tripeptidase or endopeptidase action on certain peptides, as well as the classical peptidyl dipeptidase activity. 7. Numerous potent inhibitors of the enzyme have been developed and used successfully in the treatment of hypertension, but some of the observed side effects may be due to inhibition of other zinc metalloenzymes. 8. Both endothelial and testicular ACE are highly conserved between species, indicative of the essential role(s) of the enzyme in blood pressure regulation and other physiological processes.

Effect of temperature and chloride on steady-state inhibition of angiotensin I-converting enzyme by enalaprilat and ramiprilat

The kinetics of the steady-state inhibition of angiotension I-converting enzyme (EC 3.4.15.1) at 25 degrees C and 37 degrees C with enalaprilat and ramiprilat can be simulated, assuming only one inhibitor-binding site, consistent with a 1:1 stoichiometry if the protein concentration was determined by amino acid analysis. In this temperature range the apparent inhibition constants for ramiprilat and enalaprilat were roughly doubled by a decrease in the chloride concentration from 0.300 M to 0.120 M.

Transcription of testicular angiotensin-converting enzyme (ACE) is initiated within the 12th intron of the somatic ACE gene

Angiotensin-converting enzyme (ACE) is a zinc-containing dipeptidyl carboxypeptidase that catalyzes the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. By analyzing cDNA and genomic DNA, we have constructed a consensus sequence encoding the testis isozyme of mouse ACE. Testis ACE cDNA contains 2,435 base pairs and encodes a protein of 732 amino acids. The N-terminal 66 amino acids are unique to the testis isozyme, while the remaining 666 are identical to the carboxyl half of mouse somatic ACE. The overall conservation of amino acid sequence between the testis isozymes of the mouse, rabbit, and human is 78 to 84%. The conservation of amino acids for the N-terminal domain uniquely expressed within the testis is 63 to 67% between these species. Primer extension and RNase protection experiments show that RNA transcription of the testis ACE isozyme begins 16 or 17 bases upstream from the translation start site. A sequence element resembling a TATA box is found 25 bases 5' of the transcription start site. To create its unique isozyme of ACE, the testis begins mRNA transcription in the middle of the exonic-intronic structure of somatic ACE, within a sequence treated as an intron by somatic tissues. Testis ACE is not the result of alternative RNA splicing but seems due to the start of transcription at a unique site within the ACE gene.

Transcription of testicular angiotensin-converting enzyme (ACE) is initiated within the 12th intron of the somatic ACE gene

Angiotensin-converting enzyme (ACE) is a zinc-containing dipeptidyl carboxypeptidase that catalyzes the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. By analyzing cDNA and genomic DNA, we have constructed a consensus sequence encoding the testis isozyme of mouse ACE. Testis ACE cDNA contains 2,435 base pairs and encodes a protein of 732 amino acids. The N-terminal 66 amino acids are unique to the testis isozyme, while the remaining 666 are identical to the carboxyl half of mouse somatic ACE. The overall conservation of amino acid sequence between the testis isozymes of the mouse, rabbit, and human is 78 to 84%. The conservation of amino acids for the N-terminal domain uniquely expressed within the testis is 63 to 67% between these species. Primer extension and RNase protection experiments show that RNA transcription of the testis ACE isozyme begins 16 or 17 bases upstream from the translation start site. A sequence element resembling a TATA box is found 25 bases 5' of the transcription start site. To create its unique isozyme of ACE, the testis begins mRNA transcription in the middle of the exonic-intronic structure of somatic ACE, within a sequence treated as an intron by somatic tissues. Testis ACE is not the result of alternative RNA splicing but seems due to the start of transcription at a unique site within the ACE gene.

Two putative active centers in human angiotensin I-converting enzyme revealed by molecular cloning

The amino-terminal amino acid sequence and several internal peptide sequences of angiotensin I-converting enzyme (ACE; peptidyl-dipeptidase A, kininase II; EC 3.4.15.1) purified from human kidney were used to design oligonucleotide probes. The nucleotide sequence of ACE mRNA was determined by molecular cloning of the DNA complementary to the human vascular endothelial cell ACE mRNA. The complete amino acid sequence deduced from the cDNA contains 1306 residues, beginning with a signal peptide of 29 amino acids. A highly hydrophobic sequence located near the carboxyl-terminal extremity of the molecule most likely constitutes the anchor to the plasma membrane. The sequence of ACE reveals a high degree of internal homology between two large domains, suggesting that the molecule resulted from a gene duplication. Each of these two domains contains short amino acid sequences identical to those located around critical residues of the active site of other metallopeptidases (thermolysin, neutral endopeptidase, and collagenase) and therefore bears a putative active site. Since earlier experiments suggested that a single Zn atom was bound per molecule of ACE, only one of the two domains should be catalytically active. The results of genomic DNA analysis with the cDNA probe are consistent with the presence of a single gene for ACE in the haploid human genome. Whereas the ACE gene is transcribed as a 4.3-kilobase mRNA in vascular endothelial cells, a 3.0-kilobase transcript was detected in the testis, where a shorter form of ACE is synthesized.

Partial protein sequence of mouse and bovine kidney angiotensin converting enzyme

Angiotensin converting enzyme (ACE) plays an important role in the regulation of renal blood pressure by the hydrolysis of the inactive precursor peptide angiotensin I to the potent vasopressor angiotensin II. Renal ACE is a surface membrane protein of both endothelium and tubular epithelium. Enzymatically active ACE was isolated from renal homogenates by chromatography using an affinity column constructed by linking an ACE inhibitor, lisinopril, to Affi-Gel 15. Analysis of eluates from this column showed that ACE activity was increased greater than 500-fold. SDS-polyacrylamide gel electrophoresis demonstrated a single band of molecular weight 144 kD (mouse) and 149 kD (bovine). N-terminal amino acid sequence analysis revealed: (formula; see text) Though bovine ACE has one additional N-terminal amino acid, these two partial sequences are highly homologous (16 of 20 positions are identical). Mouse ACE was digested with trypsin and the peptides were isolated by reverse phase HPLC. Analysis of the amino acid sequences showed that these tryptic peptides were unique to ACE. Thus, we were able to isolate ACE from bovine and mouse kidneys and show that they had substantial structural homology. They were also quite similar to that from rabbit lung.

Pig kidney angiotensin converting enzyme. Purification and characterization of amphipathic and hydrophilic forms of the enzyme establishes C-terminal anchorage to the plasma membrane

Angiotensin converting enzyme from pig kidney was isolated by affinity chromatography after solubilization from the membrane by one of four different procedures. Solubilization with Triton X-100, trypsin or by an endogenous activity in microvillar membranes all generated hydrophilic forms of the enzyme as assessed by phase separation in Triton X-114 and failure to incorporate into liposomes. Only when solubilization and purification was effected by Triton X-100 in the presence of EDTA (10 mM) could an amphipathic form of the enzyme (membrane- or m-form) be generated. The m-form of angiotensin converting enzyme (ACE) appeared slightly larger (Mr approx. 180,000) than the hydrophilic forms (Mr approx. 175,000) after SDS/polyacrylamide-gel electrophoresis, and the m-form incorporated into liposomes, consistent with retention of the membrane anchor. The m-form of ACE showed an N-terminal sequence identical with that of preparations of enzyme isolated after solubilization with detergent alone (d-form), with trypsin (t-form) or by the endogenous mechanism (e-form). These data imply that ACE is anchored to the plasma membrane via its C-terminus, in contrast with the N-terminal anchorage of endopeptidase-24.11. No release of ACE from the membrane could be detected with a variety of phospholipases, including bacterial phosphatidylinositol-specific phospholipases C, although an endogenous EDTA-sensitive membrane-associated hydrolase was capable of releasing a soluble, hydrophilic, form of the enzyme.

Hybridization and partial cDNA sequence analyses of bovine lung angiotensin I-converting enzyme

The mRNA encoding angiotensin I-converting enzyme, a zinc-metallo dipeptidyl carboxyhydrolase, has been identified in extracts prepared from bovine lung tissue. Bovine lung poly(A) + mRNAs were subjected to electrophoresis and northern blot hybridization analysis using a radiolabeled synthetic 24-deoxyoligonucleotide probe complementary to eight codons for amino acids at the active-site of the enzyme (Harris, R.B. & Wilson, I.B., J. Biol. Chem. 260, 2208-2211, 1985). This amino acid sequence contains the catalytic glutamic acid residue. A single RNA species (approximately equal to 4 kb) was detected which is 1 kb larger than predicted from the molecular weight of the enzyme. The excess nucleic acid composition may be due to leader and/or trailer sequences or the RNA may encode a high molecular weight precursor form of the enzyme. We have cloned an EcoR1-HindIII digest fragment (1400 bp) of the duplex cDNA derived from the bovine lung converting enzyme poly(A) + mRNA and also Bal31 deletion fragments generated from the 1400 bp clone. Several of the Bal31 clones contain the active-site sequence codons of the enzyme and the complete cDNA sequence of one of these (72 bp) has been determined. We found the amino acid sequence at the active site to be -Phe-Thr-Glu-Leu-Ala-Asn-Ser-, containing the catalytic Glu residue. This sequence is identical with the sequence that we previously determined by manual Edman degradation analysis of the appropriate active-site peptide except that we now find Asn instead of Asp. We have sequenced 670 bp of the 1400 bp clone but have not yet overlapped the active-site sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of angiotensin-converting enzyme in the gills of rainbow trout,Salmo gairdneri (Richardson)

Several physical and chemical parameters of angiotensin-converting enzyme (ACE) were determined using a spectrophotometric assay of gill tissue homogenates from rainbow trout. This assay is based on the evolution of free hippuric acid via enzymatic cleavage of histidyl-leucine from the synthetic substrate hippuryl-l-histidyl-l-leucine (HHL). Piscine ACE exhibited enzymatic and kinetic properties similar to those reported for the partially purified mammalian enzyme. Proteolytic activity was both temperature and pH dependent and demonstrated hyperbolic kinetics with an apparent Km of 2.5 mM. Hydrolysis of HHL was activated by Cl(-) at concentrations between 20 mM and 100 mM. Captopril (1 × 10(-6) M) and MK-422 (1 × 10(-6) M) blocked trout gill ACE activity, however, EDTA was inhibitory only at high concentrations (1 × 10(-3) M). These results demonstrate that trout ACE is functionally similar to mammalian ACE and that the spectro-photometric assay for ACE developed by Cushman and Cheung can be applied to analysis of converting enzyme activity in fish tissue homogenates.

Pulmonary and testicular angiotensin-converting isoenzymes

A variant of angiotensin-converting enzyme occurs in (male) germinal cells. This testicular isozyme is catalytically similar to the widespread pulmonary-type isozyme, but contains a shorter polypeptide chain and does not appear until puberty. The two proteins differ at their NH2- and COOH-termini, but share many tryptic peptides. All antigenic determinants of the testicular form are represented in the pulmonary molecule whereas the latter contains determinants unrelated to catalysis which are lacking in the testicular species. The data indicate that the testicular isozyme corresponds closely to an internal part of the pulmonary polypeptide which includes its active site. The structural and developmental differences between the two polypeptides are pretranslationally determined since they are demonstrable in a cell-free system programmed by the appropriate mRNAs. Characterization of the molecular mechanisms responsible for the relationship of these isozymes may yield useful information regarding cell-specific protein expression.

Testicular angiotensin I-converting enzyme (E.C. 3.4.15.1)

In the two mammalian species (i.e., rabbit and rat) in which it has been studied to date, testicular angiotensin I-converting enzyme possesses distinct physicochemical and immunological properties, and a susceptibility to hormonal regulation that makes it a unique isozyme of the converting enzyme ordinarily distributed throughout the body. The testicular isozyme appears to be a lower molecular weight version of the pulmonary enzyme, with similar, although not identical, catalytic properties. The testicular isozyme is under androgenic control and is associated with germinal cells. Although its function has yet to be elaborated, the testicular isozyme provides an excellent model for the study of tissue-specific regulation of carboxypeptidases.