Structural characterization of angiotensin I-converting enzyme in complex with a selenium analogue of captopril

Revisiting the dipeptidyl carboxypeptidase inhibitor captopril as a source of pan anti-trypanosomatid agents

The protozoan parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. are responsible for continued propagation of neglected tropical diseases such as African sleeping sickness, Chagas disease and leishmaniasis respectively. Following a report that captopril targets Leishmania donovani dipeptidyl carboxypeptidase, a series of simple proline amides and captopril analogues were synthesized and found to exhibit 1-2 μM in vitro inhibition and selectivity against Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. The results were corroborated with computational docking studies. Arguably, the synthetic proline amides represent the structurally simplest examples of in vitro pan antiprotozoal compounds.

A novel heat-stable angiotensin-converting enzyme zinc-binding motif inhibitory peptide identified from corn silk

ETHNOPHARMACOLOGICAL RELEVANCE

Hypertension is the most common and chronic severe health problem globally. Corn silk (CS), the silky fibers of corn (Zea mays L.), has a long history of traditional usage as a remedy for edema and hypertension.

AIM OF THE STUDY

The aim of the study was to explore the underlying mechanism by which CS exerts its anti-hypertensive effects and investigate the presence of bioactive molecules in CS aqueous extract.

MATERIALS AND METHODS

We analyzed the effects of boiling water extract of CS on angiotensin-converting enzyme (ACE) activities, the critical enzyme involved in the regulation of blood pressure. ACE inhibitory peptides from CS extract were identified using proteomics and bioinformatics tools. The binding interfaces between these peptides and ACE were defined by hydrogen-deuterium exchange mass spectrometry (HDX-MS). Subsequently, the anti-hypertensive effects of peptides were further investigated in spontaneously hypertensive rats (SHR).

RESULTS

Our data showed that CS extract exhibited dose-dependent inhibition of ACE activity. Liquid chromatography-tandem mass spectrometry identified a heat-stable peptide bank with 1313 distinct peptide fragments within the CS boiling water extract. Among these, CS-1 (LVPGWTKPICIGR) was selected through PeptideRanker and BIOPEP-UWM analyses. In vitro ACE inhibitory assays confirmed that CS-1 exhibited dose-dependent ACE inhibition, with IC50 values of 10.32 ± 0.41 μmol/L (using HHL as the substrate) and 13.74 ± 1.87 μmol/L (using ZFHL as the substrate). Oral administration of CS-1 led to a significant dose-dependent reduction in blood pressure, with the maximal decrease (42.33 ± 13.08 mmHg) occurring 0.5 h after ingestion. HDX-MS analysis revealed that CS-1 interacted with the zinc-binding motif of ACE, and hydrogen bond interactions were predicted between CS-1 and specific residues, including His361 in the N-domain, as well as His382, Gly386, and His387 in the C-domain of ACE. These findings suggested that the interaction of CS-1 with the residues in the zinc-binding motif of ACE led to ACE activity inhibition and a subsequent decrease in blood pressure in rats.

CONCLUSIONS

A novel heat-stable ACE inhibitory peptide, which interacted with the zinc-binding motif of ACE and reduced blood pressure in SHR, was identified in the CS extract. The presence of ACE inhibitory peptides in the CS extract supports its traditional use in ethnopharmacology for hypertension.

In silico identification of antidiabetic and hypotensive potential bioactive peptides from the sheep milk proteins-a molecular docking study

An in silico approach was used for hydrolysis of sheep milk proteins (α-s1, α-s2, β-casein, κ-Cn, α-lactalbumin, and β-lactoglobulin) by gastrointestinal enzymes in order to generate bioactive peptides (BAPs) that can inhibit ACE and DPP-IV. Sheep milk proteins showed higher similarity with goat milk proteins. These data were acquired via the Clustal Omega tool to perform sequence alignment analysis. The BIOPEP-UWM database was used to examine the ability of sheep milk protein sequences to generate BAPs, which included a description of their potential bioactivity as well as the frequency of fragments with specified activities. Using the "Enzyme(s) action" tool (BIOPEP-UWM), digestive enzymes pepsin, trypsin, and chymotrypsin, and three enzyme combinations were selected to computationally hydrolyze milk proteins for obtaining information about ACE and DPP-IV inhibitory peptides. Other online programs were used to test potential peptides for bioactivity, toxicity, and physicochemical properties. BAPs produced from PTC-hydrolyzed proteins were analyzed using a peptide ranker, and their inhibitory effects on ACE and DPP-IV were determined using molecular docking. Consequently, the results of molecular docking analysis show that the peptide PSGAW (αS1-Cn f155-159) binds to DPP-IV with binding energy (-8.9 kcal/mol). But in the case of ACE, two potential BAPs were selected: QPPQPL (β-Cn f161-166) and PSGAW. These two BAPs revealed a higher binding affinity for ACE with a binding energy of -9.8 kcal/mol. Thus, the results showed that sheep milk proteins were a promising source of antidiabetic and hypotensive peptides. However, experimental and pre-clinical studies are necessary to assay their therapeutic effects. PRACTICAL APPLICATIONS: Sheep milk proteins are known as a high-quality milk protein resource. Effective enzymatic hydrolysis of sheep milk proteins can release bioactive peptides and also release potential ACE and DPP-IV inhibitory peptides. This in silico study specifies a theoretical root for sheep milk proteins as a novel source of potential bioactive peptides and may offer guidance for invitro hydrolysis of proteins for the production of bioactive peptides valuable for human consumption.

ACE and ACE2: insights from Drosophila and implications for COVID-19

Angiotensin-converting enzyme (ACE) and its homologue ACE2 are key regulators of the renin-angiotensin system and thereby cardiovascular function through their zinc-metallopeptidase activity on vasoactive peptides. ACE2 also serves as the receptor for the cellular entry of various coronaviruses including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the coronavirus disease 2019 (COVID-19). The unprecedented scale of the COVID-19 pandemic has spurred the use of mammalian models to investigate the SARS-ACE2 relationship and knowledge gained from such research has accelerated development of vaccines and therapeutics. Recent studies have just started to underscore the utility of the fruit fly Drosophila melanogaster as a model system to study virus-host interactions and pathogenicity. Notably, the remarkable existence of catalytically functional ACE and ACE2 orthologues in Drosophila, discovered more than two decades ago, provides a unique opportunity for further developing this model organism to better understand COVID-19 in addition to identifying coronavirus preventative and therapeutic interventions targeting ACE2. Here, we review the studies that revealed crucial insights on the biochemistry and physiology of Ance and Acer, two out of the six Drosophila ACE family members with the greatest homology to human ACE and ACE2. We highlight shared in vivo functions outside of the renin-angiotensin system, which is not conserved in flies. Importantly, we identify knowledge gaps that can be filled by further research and outline ways that can raise Drosophila to a powerful model system to combat SARS-CoV-2 and its threatening vaccine-evading variants.

Antihypertensive Effects of Dehydroabietic and 4-Epi-Trans-Communic Acid Isolated from Pinus densiflora

Korean red pine needle (RPN) exhibits various biological and pharmacological activities. Among the various compounds of RPN, we isolated dehydroabietic and 4-epi-trans-communic acid. At first, we confirmed that two compounds inhibited angiotensin converting enzyme (ACE) and induced p-Akt in human umbilical vein endothelial cells (HUVEC). RPN extract powder significantly reduced systolic blood pressure in spontaneous hypertensive rats (SHRs) through the reduced expression of ACE and angiotensin type I receptors in the lungs of SHRs. The Lineweaver-Burk plots suggested that the two compounds were noncompetitive inhibitors of ACE. Using docking analysis, we found that two compounds showed the best returned pose at ACE active sites, and formed hydrogen and hydrophobic bonds with ACE residues. These results demonstrate that RPNs may be a source of compounds effective for preventing hypertension and may be useful in the development of antihypertensive drugs.

Assessment of the Multifunctional Behavior of Lupin Peptide P7 and Its Metabolite Using an Integrated Strategy

LTFPGSAED (P7) is a multifunctional hypocholesterolemic and hypoglycemic lupin peptide. While assessing its angiotensin-converting enzyme (ACE) inhibitory activity, it was more effective in intestinal Caco-2 cells (IC₅₀ of 13.7 μM) than in renal HK-2 cells (IC₅₀ of 79.6 μM). This discrepancy was explained by the metabolic transformation mediated by intestinal peptidases, which produced two main detected peptides, TFPGSAED and LTFPG. Indeed LTFPG, dynamically generated by intestinal dipeptidyl peptidase IV as well as its parent peptide P7 were linearly absorbed by mature Caco-2 cells. An in silico study demonstrated that the metabolite was a better ligand of the ACE enzyme than P7. These results are in agreement with an in vivo study, previously performed by Aluko et al., which has shown that LTFPG is an effective hypotensive peptide. Our work highlights the dynamic nature of bioactive food peptides that may be modulated by the metabolic activity of intestinal cells.

ACE2 and ACE: structure-based insights into mechanism, regulation and receptor recognition by SARS-CoV

Angiotensin converting enzyme (ACE) is well-known for its role in blood pressure regulation via the renin–angiotensin aldosterone system (RAAS) but also functions in fertility, immunity, haematopoiesis and diseases such as obesity, fibrosis and Alzheimer’s dementia. Like ACE, the human homologue ACE2 is also involved in blood pressure regulation and cleaves a range of substrates involved in different physiological processes. Importantly, it is the functional receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 responsible for the 2020, coronavirus infectious disease 2019 (COVID-19) pandemic. Understanding the interaction between SARS-CoV-2 and ACE2 is crucial for the design of therapies to combat this disease. This review provides a comparative analysis of methodologies and findings to describe how structural biology techniques like X-ray crystallography and cryo-electron microscopy have enabled remarkable discoveries into the structure–function relationship of ACE and ACE2. This, in turn, has enabled the development of ACE inhibitors for the treatment of cardiovascular disease and candidate therapies for the treatment of COVID-19. However, despite these advances the function of ACE homologues in non-human organisms is not yet fully understood. ACE homologues have been discovered in the tissues, body fluids and venom of species from diverse lineages and are known to have important functions in fertility, envenoming and insect–host defence mechanisms. We, therefore, further highlight the need for structural insight into insect and venom ACE homologues for the potential development of novel anti-venoms and insecticides.

Blood pressure-lowering effects of a Bowman-Birk inhibitor and its derived peptides in normotensive and hypertensive rats

Bioactive plant peptides have received considerable interest as potential antihypertensive agents with potentially fewer side effects than antihypertensive drugs. Here, the blood pressure-lowering effects of the Bowman-Birk protease inhibitor, BTCI, and its derived peptides, PepChy and PepTry, were investigated using normotensive (Wistar-WR) and spontaneously hypertensive rats (SHR). BTCI inhibited the proteases trypsin and chymotrypsin, respectively, at 6 µM and 40 µM, a 10-fold greater inhibition than observed with PepTry (60 µM) and PepChy (400 µM). These molecules also inhibited angiotensin converting enzyme (ACE) with IC50 values of 54.6 ± 2.9; 24.7 ± 1.1; and 24.4 ± 1.1 µM, respectively, occluding its catalytic site, as indicated by molecular docking simulation, mainly for PepChy and PepTry. Gavage administration of BTCI and the peptides promoted a decrease of systolic and diastolic blood pressure and an increase of renal and aortic vascular conductance. These effects were more expressive in SHR than in WR. Additionally, BTCI, PepChy and PepTry promoted coronary vasodilation and negative inotropic effects in isolated perfused hearts. The nitric oxide synthase inhibitor blunted the BTCI and PepChy, with no cardiac effects on PepTry. The findings of this study indicate a therapeutic potential of BTCI and its related peptides in the treatment of hypertension.

Supramolecular insight into the substitution of sulfur by selenium, based on crystal structures, quantum-chemical calculations and biosystem recognition

Statistical analysis of data from crystal structures extracted from the Cambridge Structural Database (CSD) has shown that S and Se atoms display a similar tendency towards specific types of interaction if they are part of a fragment that corresponds to the side chains of cysteine (Cys), methionine (Met) selenocysteine (Sec) and selenomethionine (Mse). The most numerous are structures with C-H...Se and C-H...S interactions (∼80%), notably less numerous are structures with Se...Se and S...S interactions (∼5%), and Se...π and S...π interactions are the least numerous. The results of quantum-chemical calculations have indicated that C-H...Se (∼-0.8 kcal mol^-1) and C-H...S interactions are weaker than the most stable parallel interaction (∼-3.3 kcal mol^-1) and electrostatic interactions of σ/π type (∼-2.6 kcal mol^-1). Their significant presence can be explained by the abundance of CH groups compared with the numbers of Se and S atoms in the crystal structures, and also by the influence of substituents bonded to the Se or S atom that further reduce their possibilities for interacting with species from the environment. This can also offer an explanation as to why O-H...Se (∼-4.4 kcal mol^-1) and N-H...Se interactions (∼-2.2 kcal mol^-1) are less numerous. Docking studies revealed that S and Se rarely participate in interactions with the amino acid residues of target enzymes, mostly because those residues preferentially interact with the substituents bonded to Se and S. The differences between Se and S ligands in the number and positions of their binding sites are more pronounced if the substituents are polar and if there are more Se/S atoms in the ligand.

Dipeptidyl peptidase-4 inhibitors can inhibit angiotensin converting enzyme

Angiotensin-1 converting enzyme inhibitors (ACEIs) improve insulin sensitivity. Inhibitors of dipeptidyl peptidase-4 (DPP-4) are anti-diabetic drugs with several cardio-renal effects. Both ACE and DPP-4 share common features. Thus, we tested if they could be inhibited by one inhibitor. First, in silico screening was used to investigate the ability of different DPP-4 inhibitors or ACEIs to interact with DPP-4 and ACE. The results of screening were then extrapolated into animal study. Fifty Sprague Dawley rats were randomly assigned into 5 groups treated with vehicle, captopril, enalapril, linagliptin or sitagliptin. Both low and high doses of each drug were tested. Baseline blood samples and samples at days 1, 8, 10, 14 were used to measure plasma DPP-4 and ACE activities and angiotensin II levels. Active glucagon-like peptide-1 (GLP-1) levels were measured after oral glucose challenge. All tested DPP-4 inhibitors could interact with ACE at a relatively reasonable binding energy while most of the ACEIs only interacted with DPP-4 at a predicted high inhibition constant. In rats, high dose of sitagliptin was able to inhibit ACE activity and reduce angiotensin II levels while linagliptin had only a mild effect. ACEIs did not significantly affect DPP-4 activity or prevent GLP-1 degradation. It seems that some DPP-4 inhibitors could inhibit ACE and this could partially explain the cardio-renal effects of these drugs. Further studies are required to determine if such inhibition could take place in clinical settings.

Advances in Structural Biology of ACE and Development of Domain Selective ACE-inhibitors

BACKGROUND

The Angiotensin-I converting enzyme (ACE) is one of the most important components of the renin-angiotensin-aldosterone system controlling blood pressure and renal functions. Inhibitors of ACE are first line therapeutics used in the treatment of hypertension and related cardiovascular diseases. Somatic ACE consists of two homologous catalytic domains, the C- and N-domains. Recent findings have shown that although both domains are highly homologous in structure, they may have different physiological functions. The C-domain is primarily involved in the control of blood pressure, in contrast to the N-domain that is engaged in the regulation of hematopoietic stem cell proliferation. The currently available ACE inhibitors have some adverse effects that can be attributed to the non-selective inhibition of both domains. In addition, specific Ndomain inhibitors have emerged as potential antifibrotic drugs. Therefore, ACE is still an important drug target for the development of novel domain-selective drugs not only for the cardiovascular system but also for other systems.

OBJECTIVE

Detailed structural information about interactions in the protein-ligand complex is crucial for rational drug design. This review highlights the structural information available from crystallographic data which is essential for the development of domain selective inhibitors of ACE.

METHODS

Over eighty crystal complexes of ACE are placed into the Protein Database. An overview of X-ray ACE complexes with various inhibitors in C- and N-domains and an analysis of their binding mode have given mechanistic explanation of the structural determinants of selective ligand binding. In addition, ACE domain selective inhibitors with dual modes of action in complexes with ACE are also discussed.

CONCLUSION

Selectivity of ACE inhibitors for the N- and C-domain is controlled by subtle differences in the amino-acids forming the active site. Reported studies of crystal complexes of inhibitors in the C- and N-domains revealed that most selective inhibitors interact with non-conserved amino-acids between domains and have distinct interactions with the residues in the S2 and S2' subsites of the ACE catalytic site. Moreover, unusual binding of the second molecule of inhibitors in the binding cavity opens new possibilities of exploiting more distant regions of the catalytic center in structure-based design of novel drugs.

Angiotensin-converting enzyme Ance is cooperatively regulated by Mad and Pannier in Drosophila imaginal discs

Angiotensin-converting enzyme (ACE) is an evolutionarily conserved peptidyl dipeptidase. Mammalian ACE converts angiotensin I to the active vasoconstrictor angiotensin II, thus playing a critical role for homeostasis of the renin-angiotensin system. In Drosophila, the ACE homolog Ance is expressed in specific regions of developing organs, but its regulatory mechanism has not been identified. Here we provide evidence that Ance expression is regulated by a combination of Mad and Pannier (Pnr) in imaginal discs. We demonstrate that Ance expression in eye and wing discs depends on Dpp signaling. The Mad binding site of Ance regulatory region is essential for Ance expression. Ance expression in imaginal discs is also regulated by the GATA family transcription factor Pnr. Pnr directly regulates Ance expression by binding to a GATA site of Ance enhancer. In addition, Pnr and Mad physically and genetically interact. Ance null mutants are morphologically normal but show genetic interaction with dpp mutants. Furthermore, we show that human SMAD2 and GATA4 physically interact and ACE expression in HEK293 cells is regulated by SMAD2 and GATA4. Taken together, this study reveals a cooperative mechanism of Ance regulation by Mad and Pnr. Our data also suggest a conserved transcriptional regulation of human ACE.

Pathological interactions between the endothelin-1 and the angiotensin- converting enzyme among Tunisian coronary patients

Background

The correct understanding of the biochemical and metabolic interactions between coronary risk factors contribute to the exploration of cardiovascular pathophysiology and improves therapeutic care.

The aim of this study was to explore the endothelin-1 (ET-1) concentration and the angiotensin converting enzyme (ACE) activity among Tunisian patients with coronary heart disease, and to investigate the metabolic relationships between these two markers,… and to assess the possible relationship between them and the different risk factors.

In this present study, ET-1 concentration was determined by an analytical method (High Performance Chromatography, coupled by Mass Spectrometry), ACE activity was measured by a kinetic method for patients and healthy controls. These subjects (157 patients and 142 controls) beneficed also by a biochemical exploration (lipid, apolipoproteins and glucose profiles) to quantify cardiovascular risk.

Results

A statistically significant increase of the ET-1 concentration was found among patients compared to healthy controls (15.2 ± 5.3 nM vs 7.1 ± 2.7 nM, p < 0,00001). For the ACE activity, in spite the treatment of the majority of patients (97%) with ACE inhibitors, this activity was statistically elevated in patients compared to healthy subjects (86.7 ± 25.4 IU/L vs 42.8 ± 12.1 IU/L, p < 0.00001).

Furthermore, a statistically positive correlation was identified between these two cardiac markers (r = 0.68 p < 0.00001).

Conclusion

The study of the metabolic relationship between the ET-1 and ACE among coronary patients reveals other therapeutics targets.

A Novel Vasoactive Proline-Rich Oligopeptide from the Skin Secretion of the Frog Brachycephalus ephippium

Proline-rich oligopeptides (PROs) are a large family which comprises the bradykinin-potentiating peptides (BPPs). They inhibit the activity of the angiotensin I-converting enzyme (ACE) and have a typical pyroglutamyl (Pyr)/proline-rich structure at the N- and C-terminus, respectively. Furthermore, PROs decrease blood pressure in animals. In the present study, the isolation and biological characterization of a novel vasoactive BPP isolated from the skin secretion of the frog Brachycephalus ephippium is described. This new PRO, termed BPP-Brachy, has the primary structure WPPPKVSP and the amidated form termed BPP-BrachyNH₂ inhibits efficiently ACE in rat serum. In silico molecular modeling and docking studies suggest that BPP-BrachyNH₂ is capable of forming a hydrogen bond network as well as multiple van der Waals interactions with the rat ACE, which blocks the access of the substrate to the C-domain active site. Moreover, in rat thoracic aorta BPP-BrachyNH₂ induces potent endothelium-dependent vasodilatation with similar magnitude as captopril. In DAF-FM DA-loaded aortic cross sections examined by confocal microscopy, BPP-BrachyNH₂ was found to increase the release of nitric oxide (NO). Moreover, BPP-BrachyNH₂ was devoid of toxicity in endothelial and smooth muscle cell cultures. In conclusion, the peptide BPP-BrachyNH₂ has a novel sequence being the first BPP isolated from the skin secretion of the Brachycephalidae family. This opens for exploring amphibians as a source of new biomolecules. The BPP-BrachyNH₂ is devoid of cytotoxicity and elicits endothelium-dependent vasodilatation mediated by NO. These findings open for the possibility of potential application of these peptides in the treatment of endothelial dysfunction and cardiovascular diseases.

Hybrid in Silico/in Vitro Approach for the Identification of Angiotensin I Converting Enzyme Inhibitory Peptides from Parma Dry-Cured Ham

The bioactivity assessment of foodborne peptides is currently a research area of great relevance, and, in particular, several studies are devoted to the antihypertensive effects through the inhibition of angiotensin I converting enzyme (ACE). In the present work, a straightforward workflow to identify inhibitory peptides from food matrices is proposed, which involves a hybrid in vitro/in silico tandem approach. Parma dry-cured ham was chosen as case study. In particular, the advantage of using the hybrid approach to identify active sequences (in comparison to the experimental trials alone) has been pointed out. Specifically, fractions obtained by in vitro gastrointestinal digestion of ham samples of 18 and 24 months of aging have been assessed for ACE inhibition. At the same time, the released peptidomic profiles, which cannot be entirely evaluated by using in vitro assays, have been screened for the inhibition by using an in silico model. Then, to identify novel inhibitory sequences, a series of strong candidates have been synthesized and assessed for their inhibitory activity through in vitro assay. On the one hand, the use of computational simulations appeared to be an effective strategy to find active sequences, as confirmed by in vitro analysis. On the other hand, strong inhibitory sequences were identified for the first time in Parma dry-cured ham (e.g., LGL and SFVTT with IC50 values of 145 and 395 μM, respectively), which is a product of international dietary and economic relevance. Therefore, these findings demonstrate the usefulness of in silico methodologies coupled to in vitro tests for the identification of potentially bioactive peptides, and they give an important contribution to the study of the overall nutritional value of Parma ham.

Novel approaches for the identification of inhibitors of leishmanial dipeptidylcarboxypeptidase

INTRODUCTION

Leishmaniasis imposes a substantial burden of mortality and morbidity affecting 12 million globally and continues to be a neglected tropical disease. Control of the disease is mainly based on chemotherapy, which relies on a handful of drugs with serious limitations. Over the last decade, target-based drug discovery is also being employed in addition to the random screening of compounds. Leishmanial dipeptidylcarboxypeptidase (LDCP), an angiotensin converting enzyme (ACE) related metallopeptidase, has been recently identified as a novel drug target for antileishmanial chemotherapy.

AREAS COVERED

This article examines dipeptidylcarboxypeptidase (DCP) of Leishmania donovani and of other sources from the international literature regarding their biochemical and structural characterization in comparison to mammalian ACE. Furthermore, the author discusses the identification of LdDCP specific inhibitors by virtual screening and their effect on parasite multiplication. Finally, the review looks ahead at areas for further exploration of DCP inhibitors in Leishmania chemotherapy.

EXPERT OPINION

The first step in targeted screening is to identify a suitable drug target and its validation followed by its use in high throughput screening of compounds. Limited studies on LDCP inhibitors have established a good correlation between parasite enzyme inhibition and their biological activity. This suggests that there is a potential for LDCP inhibitors as new antileishmanial drugs.

Antioxidant activity of peptide-based angiotensin converting enzyme inhibitors

Angiotensin converting enzyme (ACE) inhibitors are important for the treatment of hypertension as they can decrease the formation of vasopressor hormone angiotensin II (Ang II) and elevate the levels of vasodilating hormone bradykinin. It is observed that bradykinin contains a Ser-Pro-Phe motif near the site of hydrolysis. The selenium analogues of captopril represent a novel class of ACE inhibitors as they also exhibit significant antioxidant activity. In this study, several di- and tripeptides containing selenocysteine and cysteine residues at the N-terminal were synthesized. Hydrolysis of angiotensin I (Ang I) to Ang II by ACE was studied in the presence of these peptides. It is observed that the introduction of L-Phe to Sec-Pro and Cys-Pro peptides significantly increases the ACE inhibitory activity. On the other hand, the introduction of L-Val or L-Ala decreases the inhibitory potency of the parent compounds. The presence of an L-Pro moiety in captopril analogues appears to be important for ACE inhibition as the replacement of L-Pro by L-piperidine 2-carboxylic acid decreases the ACE inhibition. The synthetic peptides were also tested for their ability to scavenge peroxynitrite (PN) and to exhibit glutathione peroxidase (GPx)-like activity. All the selenium-containing peptides exhibited good PN-scavenging and GPx activities.