Association of urinary N-domain Angiotensin I-converting enzyme with plasma inflammatory markers and endothelial function

The aim of this study was to investigate the association between urinary 90 kDa N-domain Angiotensin I-converting enzyme (ACE) form with C-reactive protein (CRP) and homocysteine plasma levels (Hcy), urinary nitric oxide (NOu), and endothelial function (EF) in normotensive subjects. Forty healthy subjects were evaluated through brachial Doppler US to test the response to reactive hyperemia and a panel of blood tests to determine CRP and Hcy levels, NOu, and urinary ACE. They were divided into groups according to the presence (ACE90+) or absence (ACE90-) of the 90 kDa ACE, the presence (FH+) or absence (FH-) of family history of hypertension, and the presence or absence of these two variables FH+/ACE90+ and FH-/ACE90-. We found an impaired endothelial dilatation in subjects who presented the 90 kDa N-domain ACE as follows: 11.4% +/- 5.3% in ACE90+ compared with 17.6% +/- 7.1% in ACE90- group and 12.4% +/- 5.6% in FH+/ACE90+ compared with 17.7% +/- 6.2% in FH-/ACE90- group, P < 0.05. Hcy and CRP levels were statistically significantly lower in FH+/ACE90+ than in FH-/ACE90- group, as follows: 10.0 +/- 2.3 microM compared with 12.7 +/- 1.5 microM, and 1.3 +/- 1.8 mg/L compared with 3.6 +/- 2.0 mg/L, respectively. A correlation between flow-mediated dilatation (FMD) and CRP, Hcy, and NOu levels was not found. Our study suggests a reduction in the basal NO production confirmed by NOu analysis in subjects with the 90 kDa N-domain ACE isoform alone or associated with a family history of hypertension. Our data suggest that the presence of the 90 kDa N-domain ACE itself may have a negative impact on flow-mediated dilatation stimulated by reactive hyperemia.     

Characterization of human epidermal growth factor in human serum and urine under native conditions

The objective of this study was to investigate the molecular nature of the human epidermal growth factor (EGF) in serum and urine samples of normal subjects. Recombinant EGF emerged as a single peak and did not interact with human IgG1 and albumin up to the concentration of 12 microg/ml. Freshly separated human serum contained only trace amounts of EGF. However, EGF appeared and increased in serum separated from blood after spontaneous overnight clotting. The authentic 6 kDa form of EGF made up nearly 40% of the total EGF in serum and revealed relatively homogeneous feature. The remaining immunoreactive fractions corresponded to 160 kDa proEGF. Immunoreactive EGF in blood seemed to be associated with the EGF release from platelets. TSKgel G3000SW chromatography of freshly-voided morning and day urines revealed that urine samples mainly contained two major form of EGF; a high-molecular-weight (HMW) and low-molecular-weight (LMW) forms. In the sense of molecular nature of EGF contents, morning urine was more heterogeneous than day urine of the same individuals. The LMW form of EGF in morning urine, in which its proportion was more than 90% of the total EGF, revealed further heterogeneous feature generally containing three to four different components.     

Physicochemical and immunological comparisons between angiotensin I-converting enzymes purified from different mammalian species

Angiotensin I-converting enzyme (ACE) was purified from lungs of pig, rat, monkey and human for comparison of its physicochemical, enzymatic and immunological properties. The protocol involved three chromatographic steps after detergent extraction, i.e. DEAE–Sphérodex ion exchange, lisinopril–Sepharose affinity and Superose 12 HPLC, plus Mono-Q HPLC for monkey ACE. Purified ACE's presented numerous homologies: in particular, closely similar specific activities, catalytic efficiencies, K_m's, optimal pH and chloride activations; the molecular weights were about 170 kDa by SDS-PAGE and 320 kDa by gel-filtration on Superose 12; the isoelectric points were about 4.5–4.7. Specific polyclonal antibodies recognized the antigen (porcine ACE) as well as rat, monkey and human ACEs. In contrast, three monoclonal antibodies (F02.4.1, F01.1.3 and F03) produced against porcine ACE showed some differences: they only reacted with pig enzyme and only one (F02.4.1) was anticatalytic. Moreover, the cross-reactivity judged on ELISA with porcine ACE characterized different epitopes specific for the porcine enzyme. In particular, the binding of F02.4.1 was not diminished by previous treatment with saturating concentrations of synthetic competitive ACE inhibitors. Thus, the extrapolation to human of data obtained on animal models should be possible at least for pharmacological and medical trials.     

Inhibitory antibodies to human angiotensin-converting enzyme: fine epitope mapping and mechanism of action

Angiotensin I-converting enzyme (ACE), a key enzyme in cardiovascular pathophysiology, consists of two homologous domains (N and C), each bearing a Zn-dependent active site. We modeled the 3D-structure of the ACE N-domain using known structures of the C-domain of human ACE and the ACE homologue, ACE2, as templates. Two monoclonal antibodies (mAb), 3A5 and i2H5, developed against the human N-domain of ACE, demonstrated anticatalytic activity. N-domain modeling and mutagenesis of 21 amino acid residues allowed us to define the epitopes for these mAbs. Their epitopes partially overlap: amino acid residues K407, E403, Y521, E522, G523, P524, D529 are present in both epitopes. Mutation of 4 amino acid residues within the 3A5 epitope, N203E, R550A, D558L, and K557Q, increased the apparent binding of mAb 3A5 with the mutated N-domain 3-fold in plate precipitation assay, but abolished the inhibitory potency of this mAb. Moreover, mutation D558L dramatically decreased 3A5-induced ACE shedding from the surface of CHO cells expressing human somatic ACE. The inhibition of N-domain activity by mAbs 3A5 and i2H5 obeys similar kinetics. Both mAbs can bind to the free enzyme and enzyme-substrate complex, forming E.mAb and E.S.mAb complexes, respectively; however, only complex E.S can form a product. Kinetic analysis indicates that both mAbs bind better with the ACE N-domain in the presence of a substrate, which, in turn, implies that binding of a substrate causes conformational adjustments in the N-domain structure. Independent experiments with ELISA demonstrated better binding of mAbs 3A5 and i2H5 in the presence of the inhibitor lisinopril as well. This effect can be attributed to better binding of both mAbs with the "closed" conformation of ACE, therefore, disturbing the hinge-bending movement of the enzyme, which is necessary for catalysis.     

Monoclonal Antibodies 1G12 and 6A12 to the N-domain of human angiotensin-converting enzyme: fine epitope mapping and antibody-based detection of ACE inhibitors in human blood

Angiotensin I-converting enzyme (ACE), a key enzyme in cardiovascular pathophysiology, consists of two homologous domains (N- and C-), each bearing a Zn-dependent active site. ACE inhibitors are among the most prescribed drugs in the treatment of hypertension and cardiac failure. Fine epitope mapping of two monoclonal antibodies (mAb), 1G12 and 6A12, against the N-domain of human ACE, was developed using the N-domain 3D-structure and 21 single and double N-domain mutants. The binding of both mAbs to their epitopes on the N-domain of ACE is significantly diminished by the presence of the C-domain in the two-domain somatic tissue ACE and further diminished by the presence of sialic acid residues on the surface of blood ACE. The binding of these mAbs to blood ACE, however, increased dramatically (5-10-fold) in the presence of ACE inhibitors or EDTA, whereas the effect of these compounds on the binding of the mAbs to somatic tissue ACE was less pronounced and even less for truncated N-domain. This implies that the binding of ACE inhibitors or removal of Zn2+ from ACE active centers causes conformational adjustments in the mutual arrangement of N- and C-domains in the two-domain ACE molecule. As a result, the regions of the epitopes for mAb 1G12 and 6A12 on the N-domain, shielded in somatic ACE by the C-domain globule and additionally shielded in blood ACE by sialic acid residues in the oligosaccharide chains localized on Asn289 and Asn416, become unmasked. Therefore, we demonstrated a possibility to employ these mAbs (1G12 or 6A12) for detection and quantification of the presence of ACE inhibitors in human blood. This method should find wide application in monitoring clinical trials with ACE inhibitors as well as in the development of the approach for personalized medicine by these effective drugs.     

Purification and analysis of lung and plasma angiotensin I-converting enzyme by high-performance liquid chromatography

We purified angiotensin I-converting enzyme (ACE) from pig and human lung and plasma for comparison of some physicochemical properties between the endothelial membrane-bound form and the soluble form of the enzyme. After affinity chromatography on Sepharose CL-4B/lisinopril, gel-filtration HPLC on Superose 12 achieved homogeneity for both forms as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Whatever the source of ACE, the molecular weight was 300 +/- 40 kDa after calibration of Superose 12 with standard globular proteins and 172 +/- 4 kDa by SDS-PAGE, with or without reduction, a result suggesting interactions between the glycopolypeptide chain and the chromatographic gel possibly related to the overall shape and sugar content of the enzyme. Ion-exchange HPLC analysis on TSK-DEAE showed that the membrane-bound and soluble forms of ACE are not isoenzymes, although isoelectrofocusing did show that the isoelectric point of soluble ACE was lower than those of tissue ACE, suggesting a different glycosylation. No significant difference between porcine and human ACE appeared. HPLC methods seem to be of particular interest for the purification of ACE with a high yield and for the analysis of its putative differently glycosylated isoforms.     

Hydrolysis by somatic angiotensin-I converting enzyme of basic dipeptides from a cholecystokinin/gastrin and a LH-RH peptide extended at the C-terminus with gly-Arg/Lys-arg, but not from diarginyl insulin.

Endoproteolytic cleavage of protein prohormones often generates intermediates extended at the C-terminus by Arg-Arg or Lys-Arg, the removal of which by a carboxypeptidase (CPE) is normally an important step in the maturation of many peptide hormones. Recent studies in mice that lack CP activity indicate the existence of alternative tissue or plasma enzymes capable of removing C-terminal basic residues from prohormone intermediates. Using inhibitors of angiotensin I-converting enzyme (ACE) and CP, we show that both these enzymes in mouse serum can remove the basic amino acids from the C-terminus of CCK5-GRR and LH-RH-GKR, but only CP is responsible for converting diarginyl insulin to insulin. ACE activity removes C-terminal dipeptides to generate the Gly-extended peptides, whereas CP hydrolysis gives rise to CCK5-GR and LH-RH-GK, both of which are susceptible to the dipeptidyl carboxypeptidase activity of ACE. Somatic ACE has two similar protein domains (the N-domain and the C-domain), each with an active site that can display different substrate specificities. CCK5-GRR is a high-affinity substrate for both the N-domain and C-domain active sites of human sACE (Km of 9.4 microm and 9.0 microm, respectively) with the N-domain showing greater efficiency (kcat : Km ratio of 2.6 in favour of the N-domain). We conclude that somatic forms of ACE should be considered as alternatives to CPs for the removal of basic residues from some Arg/Lys-extended peptides.     

Novel ketomethylene inhibitors of angiotensin I-converting enzyme (ACE): inhibition and molecular modelling

Inhibition of angiotensin I-converting enzyme (ACE) has become an effective strategy in the treatment of hypertension and cardiovascular disease. Keto-ACE, a previously described C-domain selective ACE inhibitor, was used as the basis for the design, synthesis and molecular modelling of a series of novel ketomethylene derivatives for which ACE inhibition profiles and structural characterisation are reported. Ki determinations indicated that the introduction of a bulky aromatic tryptophan at the P2' position of keto-ACE significantly increased selectivity for the C-domain, while an aliphatic P2 Boc group conferred N-domain selectivity. These data were supported by the potential energies of the compounds docked with the C- and N-domains of ACE.     

Nuclear activities of basic fibroblast growth factor: potentiation of low-serum growth mediated by natural or chimeric nuclear localization signals

Human basic fibroblast growth factor (FGF-2) occurs in four isoforms: a low molecular weight (LMW FGF-2, 18 kDa) and three high molecular weight (HMW FGF-2, 22, 22.5, and 24 kDa) forms. LMW FGF-2 is primarily cytoplasmic and functions in an autocrine manner, whereas HMW FGF-2s are nuclear and exert activities through an intracrine, perhaps nuclear, pathway. Selective overexpression of HMW FGF-2 forms in fibroblasts promotes growth in low serum, whereas overexpression of LMW FGF-2 does not. The HMW FGF-2 forms have two functional domains: an amino-terminal extension and a common 18-kDa amino acid sequence. To investigate the role of these regions in the intracrine signaling of HMW FGF-2, we produced stable transfectants of NIH 3T3 fibroblasts overexpressing either individual HMW FGF-2 forms or artificially nuclear-targeted LMW FGF-2. All of these forms of FGF-2 localize to the nucleus/nucleolus and induce growth in low serum. The nuclear forms of FGF-2 trigger a mitogenic stimulus under serum starvation conditions and do not specifically protect the cells from apoptosis. These data indicate the existence of a specific role for nuclear FGF-2 and suggest that LMW FGF-2 represents the biological messenger in both the autocrine/paracrine and intracrine FGF-2 pathways.     

Urokinase separation from cell culture broth of a human kidney cell line

A single step ion-exchange chromatography on a sulfo-propyl (SP)- Sepharose column was performed to separate both the high molecular weight (HMW)- and low molecular weight (LMW)- forms of enzymatically active urokinase type plasminogen activator from human kidney (HT1080) cell culture media. The level of urokinase secreted by the cell line reached to about 145 Plough units/ml culture broth within 48 h of cultivation. The conditioned cell culture media was applied directly to the column without any prior concentration steps. Polyacrylamide gel electrophoresis of the column eluates in the presence of sodium dodecyl sulphate showed that the cell line secretes three forms of two-chain high molecular weight (HMW) urokinase of molecular weights (M(r)) 64,000, 60,900 and 55,000. In addition, two low molecular weight (LMW) forms of M(r) 22,000 and 20,000; proteolytic cleavage products of HMW, were also found. The HMW and LMW forms had intrinsic plasminogen dependent proteolytic activity as judged by zymographic analysis. The specific activity of the pooled peak fractions increased (approximately 93-fold) to values as high as 1481 Plough units/ mg protein. Both HMW as well as LMW forms were obtained in significantly high yields.     

Immunopurification and characterization of human alpha-L-iduronidase with the use of monoclonal antibodies.

alpha-L-Iduronidase from human liver was purified by a three-step five-column procedure and by immunoaffinity chromatography with a monoclonal antibody raised against purified enzyme. Seven bands identified by staining with Coomassie Blue had molecular masses of 74, 65, 60, 49, 44, 18 and 13 kDa and were present in both preparations of the liver enzyme. However, relative to the immunopurification procedure, alpha-L-iduronidase purified by the five-column procedure was considerably enriched in the 65 kDa polypeptide band. The seven bands were identified by Western-blot analysis with two different monoclonal antibodies raised against alpha-L-iduronidase. The chromatographic behaviour of alpha-L-iduronidase on the antibody column was dependent upon the quantity of enzyme loaded. Above a particular load concentration a single peak of enzyme activity was eluted, whereas at load concentrations below the critical value alpha-L-iduronidase was eluted in two peaks of activity, designated form I (eluted first) and form II (eluted second). The following properties of the two forms of alpha-L-iduronidase were determined. (1) The two forms from liver were composed of different proportions of the same seven polypeptides. (2) When individually rechromatographed on the antibody column, each form from liver shifted to a more retarded elution position but essentially retained its chromatographic behaviour relative to the other form. (3) Forms I and II of liver alpha-L-iduronidase showed no difference in their activities towards disaccharide substrates derived from two glycosaminoglycan sources, heparan sulphate and dermatan sulphate. (4) The native molecular size of forms I and II of liver alpha-L-iduronidase was 65 kDa as determined by gel-permeation chromatography. (5) Immunoaffinity chromatography of extracts of human lung and kidney resulted in the separation of alpha-L-iduronidase into two forms, each with different proportions of the seven common polypeptide species. (6) Lung forms I and II were taken up readily into cultured skin fibroblasts taken from a patient with alpha-L-iduronidase deficiency. Liver forms I and II were not taken up to any significant extent. Lung form II gave intracellular contents of alpha-L-iduronidase that were more than double those of normal control fibroblasts, whereas lung form I gave contents approximately equal to normal control values. We propose that all seven polypeptides are derived from a single alpha-L-iduronidase gene product, and that different proportions of these polypeptides can function as a single alpha-L-iduronidase entity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Epitope-dependent blocking of the angiotensin-converting enzyme dimerization by monoclonal antibodies to the N-terminal domain of ACE: possible link of ACE dimerization and shedding from the cell surface

In a biomembrane modeling system, reverse micelles, somatic ACE forms dimers via carbohydrate-mediated interaction, providing evidence for the existence of a carbohydrate-recognizing domain on the ACE molecule. We localized this putative region on the N-domain of ACE using monoclonal antibodies (mAbs) to seven different epitopes of ACE. Two mAbs, 9B9 and 3G8, directed to distinct, but overlapping, epitopes of the N-domain of ACE shielded the CRD. Only "simple" ACE-antibody complexes were found in the system. Five mAbs allowed the formation of "double" antibody-ACE-ACE-antibody complexes via carbohydrate-mediated interactions. The results were confirmed using the ACE N- and C-domains. Testicular ACE was unable to form carbohydrate-mediated ACE dimers in the reverse micelles, while the N-domain of ACE, obtained by limited proteolysis of the parent full-length ACE, retained the ability to form dimers. Furthermore, mAb 3G8, which blocked ACE dimerization in micelles, significantly inhibited ACE shedding from the surface of ACE-expressing cells. Galactose prevented ACE dimerization in reverse micelles and also affected antibody-induced ACE shedding in an epitope-dependent manner. Restricted glycosylation of somatic ACE, obtained by the treatment of CHO-ACE cells with the glucosidase inhibitor N-butyldeoxynojirimycin, significantly increased the rate of basal ACE shedding and altered antibody-induced ACE shedding. A chemical cross-linking approach was used to show that ACE is present (at least in part) as noncovalently linked dimers on the surface of CHO-ACE cells. These results suggest a possible link between putative ACE dimerization on the cell surface and the proteolytic cleavage (shedding) of ACE.     

Factors affecting struvite (MgNH4PO4.6H2O) crystallization in feline urine

Factors affecting struvite, a magnesium-ammonium-phosphate complex (MgNH(4)PO(4).6H(2)O), in feline urine were evaluated. Incubation of just "urine mineral (UM)" solution, in which mineral concentrations are compatible with those in feline urine, for 4 h at 37 degrees C did not induce the formation of crystals. Similarly, incubation of urine alone did not produce crystals. However, struvite crystals were formed by the addition of urine to UM solution. Mg, NH(3) and P were all required for urine-induced struvite crystallization. The lower molecular weight (LMW) fraction of urine was essential for struvite crystal formation, and the higher molecular weight (HMW) fraction enhanced formation of LMW-induced struvite crystals. The effects of urine proteins further fractionated by column chromatography were examined. A protein at >250 kDa and cauxin, a major urine protein recently identified as a regulator of felinine production, potentiated struvite crystal formation induced by the LMW fraction. In contrast, Tamm-Horsfall glycoprotein, a urine protein thought to promote struvite crystallization, did not have this activity. The present study reveals a novel mechanism of feline struvite crystallization.     

Biosynthetic analysis of the human interferon-gamma receptor. Identification of N-linked glycosylation intermediates

Biosynthesis of the human IFN gamma receptor was studied using metabolic labeling techniques and immunoprecipitation with receptor-specific monoclonal antibodies. Colo-205 and HepG2 cells labeled with [35S]methionine gave rise to two components with molecular mass 75 and 90 kDa following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No bands were detected when immunoprecipitation was performed using irrelevant monoclonal IgG or in the presence of excess ligand, a condition known to block antibody-receptor interaction. When Colo-205 were labeled for increasing periods of time, the 75-kDa form was detected after 5 min, whereas the 90-kDa form appeared only after 60 min. Pulse-chase analysis established that the 75-kDa form was the precursor of the 90-kDa component. Only the 90-kDa form was detected on extrinsically radioiodinated Colo-205 cell surfaces. This observation was confirmed by Western blot analysis of isolated Colo-205 membranes. Digestion of labeled precipitates with peptide:N-glycosidase F caused a 22% reduction in the apparent molecular weight of the IFN gamma receptor. Receptor derived from tunicamycin-treated Colo-205 labeled for 5 min displayed a single molecular mass of 65 kDa and expressed ligand binding activity. Longer labeling periods in the presence of tunicamycin revealed the appearance of a second ligand-binding form of 70 kDa. Thus, Colo-205 IFN gamma receptors carry asparagine (N)-linked oligosaccharides and possibly some other form of post-translational modification.     

Tissue Specificity of Human Angiotensin I-Converting Enzyme

Background

Angiotensin-converting enzyme (ACE), which metabolizes many peptides and plays a key role in blood pressure regulation and vascular remodeling, as well as in reproductive functions, is expressed as a type-1 membrane glycoprotein on the surface of endothelial and epithelial cells. ACE also presents as a soluble form in biological fluids, among which seminal fluid being the richest in ACE content - 50-fold more than that in blood.

Methods/Principal Findings

We performed conformational fingerprinting of lung and seminal fluid ACEs using a set of monoclonal antibodies (mAbs) to 17 epitopes of human ACE and determined the effects of potential ACE-binding partners on mAbs binding to these two different ACEs. Patterns of mAbs binding to ACEs from lung and from seminal fluid dramatically differed, which reflects difference in the local conformations of these ACEs, likely due to different patterns of ACE glycosylation in the lung endothelial cells and epithelial cells of epididymis/prostate (source of seminal fluid ACE), confirmed by mass-spectrometry of ACEs tryptic digests.

Conclusions

Dramatic differences in the local conformations of seminal fluid and lung ACEs, as well as the effects of ACE-binding partners on mAbs binding to these ACEs, suggest different regulation of ACE functions and shedding from epithelial cells in epididymis and prostate and endothelial cells of lung capillaries. The differences in local conformation of ACE could be the base for the generation of mAbs distingushing tissue-specific ACEs.     

Low-molecular weight peptides isolated from seahorse (Hippocampus abdominalis) improve vasodilation via inhibition of angiotensin-converting enzyme in vivo and in vitro

According to relevant literature, the consumption of seahorses has been used to increase male functions by improving blood flow and decreasing blood pressure. Thus, it was theorized that seahorses may also be effective against hypertension. Herein, vasodilation caused via the inhibitory effect of angiotensin-converting enzymes (ACEs) in peptides was elucidated by studying the seahorses (Hippocampus abdominalis) farmed at Jeju in South Korea. Hydrolysate was prepared using the Protamex (SHP) enzyme. The ultrafiltration system was adopted to separate certain fractions from SHP according to different molecular weights (SHP-I, MW > 10 kDa; SHP-II, MW = 5−10 kDa; SHP-III, MW < 5 kDa). The fraction with the lowest molecular weight (SHP-III) and with a low IC₅₀ value (0.044 ± 0.005) for the ACE inhibitory effect was further separated by Sephadex G-10. Three ACE inhibitory peptides from SHP-III were isolated and identified using the Q-TOF mass spectrometer (Ala-Pro-Thr-Leu, Cys-Asn-Val-Pro-Leu-Ser-Pro, and Pro-Trp-Thr-Pro-Leu). Furthermore, SHP-III-induced systolic blood pressure varied with the concentrations, as observed in the spontaneously hypertensive rat (SHR). SHP and the isolated peptides were observed to show vasodilation via ACE inhibitions and resulted in lowering the blood pressure of the SHR. These results imply that peptides from seahorses can augment male functions.     

Stimulation of rat hepatocyte proliferation in vitro and in vivo by factors derived from the bovine small intestinal mucosa

Summary A factor with a molecular weight of less than 1 kDa in the mucosa of the bovine small intestine (low molecular weight factor or LMW factor) stimulated DNA synthesis in rat hepatocytes in primary culture. This factor only showed its activity when it was added with a larger factor with a molecular weight of 30 kDa that was also found in the same tissue (high molecular weight factor or HMW factor). The LMW factor probably acts to enhance the action of a hepatotrophic growth factor, since EGF and HGF can substitute for the HMW factor. The action of the LMW factor was not due to the actions of low molecular weight substances such as norepinephrine, estradiol, triiodothyronine, and putrescine, which enhance the action of EGF or HGF, since substantial amounts of these substances were not found in the extract. When intraperitoneally administered into rats, after two-thirds hepatectomy, the LMW factor enhanced hepatocyte proliferation without the administration of the HMW factor. In the regenerating liver, a hepatotrophic growth factor(s), which acts synergistically with the LMW factor, might be properly provided, but the supply of the LMW factor might be below the level that maximally stimulates hepatocyte proliferation.     

Peptidase specificity characterization of C- and N-terminal catalytic sites of angiotensin I-converting enzyme

Quenched fluorescence peptides were used to investigate the substrate specificity requirements for recombinant wild-type angiotensin I-converting enzyme (ACE) and two full-length mutants bearing a single functional active site (N- or C-domain). We assayed two series of bradykinin-related peptides flanked by o-aminobenzoic acid (Abz) and N-(2,4-dinitrophenyl)ethylenediamine (EDDnp), namely, Abz-GFSPFXQ-EDDnp and Abz-GFSPFRX-EDDnp (X = natural amino acids), in which the fluorescence appeared when Abz/EDDnp are separated by substrate hydrolysis. Abz-GFSPFFQ-EDDnp was preferentially hydrolyzed by the C-domain while Abz-GFSPFQQ-EDDnp exhibits higher N-domain specificity. Internally quenched fluorescent analogues of N-acetyl-SDKP-OH were also synthesized and assayed. Abz-SDK(Dnp)P-OH, in which Abz and Dnp (2,4-dinitrophenyl) are the fluorescent donor-acceptor pair, was cleaved at the D-K(Dnp) bond with high specificity by the ACE N-domain (k(cat)/K(m) = 1.1 microM(-)(1) s(-)(1)) being practically resistant to hydrolysis by the C-domain. The importance of hydroxyl-containing amino acids at the P(2) position for N-domain specificity was shown by performing the kinetics of hydrolysis of Abz-TDK(Dnp)P-OH and Abz-YDK(Dnp)P-OH. The peptides Abz-YRK(Dnp)P-OH and Abz-FRK(Dnp)P-OH which were hydrolyzed by wild-type ACE with K(m) values of 5.1 and 4.0 microM and k(cat) values of 246 and 210 s(-)(1), respectively, have been shown to be excellent substrates for ACE. The differentiation of the catalytic specificity of the C- and N-domains of ACE seems to depend on very subtle variations on substrate-specific amino acids. The presence of a free C-terminal carboxyl group or an aromatic moiety at the same substrate position determines specific interactions with the ACE active site which is regulated by chloride and seems to distinguish the activities of both domains.     

Presence of several cellulose-binding proteins in culture supernatant and cell lysate of Eubacterium cellulosolvens 5

Attempts were made to separate and characterize cellulose-binding proteins (CBPs) from both the culture supernatant and cell lysate of Eubacterium cellulosolvens 5. Once the CBPs were bound to Avicel cellulose, they were then effectively eluted with the solution containing 3.2 or 5% sodium dodecyl sulfate (SDS), but not eluted with the solution containing various kinds of carbohydrates and reagents. Namely, CBPs in both the culture supernatant and cell lysate of the bacterium bound tightly and strongly to cellulose. The SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the eluted CBPs indicated that the CBPs contained the two major proteins having the molecular weights of approximately 160 and 84 kilodaltons (kDa) and one sub-major protein having a molecular weight of approximately 140 kDa. Zymogram analysis after the SDS-PAGE of the eluted CBPs showed that two proteins exhibited the highest levels of carboxymethyl cellulase (CMCase) activity corresponding to the molecular weights of approximately 160 and 90 kDa. A major protein having the molecular weight of approximately 160 kDa exhibited a distinct CMCase activity and was designated as CBPE1. Western immunoblot analysis indicated that the proteins prepared from 16 representative strains of rumen bacteria did not cross-react with rabbit antiserum raised against CBPE1. Thus, CBPE1 may be a unique CBP that plays an important role in the adhesion of the bacterium to cellulose.     

cDNA and derived amino acid sequence of the hypusine containing protein from Dictyostelium discoideum

The eukaryotic translation initiation factor eIF-4D is the only protein known to contain the unusual amino acid hypusine, a posttranslationally modified lysine. For the production of monoclonal antibodies the hypusine-containing protein (HP) was isolated from Dictyostelium discoideum. Using these monoclonal antibodies, a full-length cDNA clone was isolated from a lambda gt11 library. The D. discoideum HP consists of 169 amino acids and has a molecular mass of 18.3 kDa. It is encoded by a single gene. Tryptic and cyanogen bromide peptides were prepared from the purified protein and sequenced. The hypusine residue is located at amino acid position 65 of the HP. The corresponding mRNA of approx. 0.6 kb is present throughout the life cycle of D. discoideum.