Isolation and Characterization of Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides from the Enzymatic Hydrolysate of Carapax Trionycis (the Shell of the Turtle Pelodiscus sinensis)

Angiotensin converting enzyme (ACE) inhibitory peptide from the tuna (Thunnus thynnus) muscle: Screening, interaction mechanism and stability

In this study, the purpose was to screen novel angiotensin converting enzyme inhibitory peptides (ACEIPs) from tuna muscle taking two-steps enzymatic hydrolysis (Neutrase and Alkaline). Following isolation and purification by ultrafiltration, the Sephadex G-15 gel chromatography and reversed-phase high-performance liquid chromatography based on active-guide, the amino acid sequence was identified using Q-Orbitrap-MS/MS. Five peptides were chose synthesized based on the in silico screening methods. Among these, the two novel ACEIPs LTGCP and YPKP showed better inhibitory ability, and their corresponding IC50 values were 64.3 μM and 139.6 μM. Subsequently, the interaction mechanism of the best active peptide (LTGCP) against ACE was investigated by inhibitory pattern, molecular docking and molecular dynamic simulation. The result displayed that LTGCP was a mix-type inhibitor against ACE from the Lineweaver-Burk plots. LTGCP formed seven hydrogen bonds based on the molecular docking and the binding energy was -7.29 kcal/mol. LTGCP formed a stability complex with ACE based on the molecular dynamic simulation. Besides, LTGCP exhibited good stability in various temperature, pH and gastrointestinal digestion. Finally, the 0.125 mM ∼ 1.0 mM LTGCP exhibited no-toxic for Caco-2 cell. In summary, these findings showed that tuna was a good material to prepare ACEIPs and LTGCP may be the good potential antihypertensive drug or nutraceuticals.

The first bioactive (angiotensin-converting enzyme-inhibitory) peptide isolated from pearl matrix protein

In this research, we unveil the medical potential of pearls by identifying a novel bioactive peptide within them for the first time. The peptide, termed KKCHFWPFPW, emerges as a pioneering angiotensin I-converting enzyme (ACE) inhibitor, originating from the pearl matrix of Pinctada fucata. Employing quadrupole time-of-flight mass spectrometry, this peptide was meticulously selected and pinpointed. With a molecular weight of 1417.5 Da and a theoretical isoelectric point of 9.31, its inhibitory potency was demonstrated through a half-maximal inhibitory concentration (IC50) of 4.17 μM, established via high-performance liquid chromatography. The inhibition of ACE by this peptide was found to be competitive, as revealed by Lineweaver-Burk plot analysis, where an increase in peptide concentration correlated with an enhanced rate of ACE inhibition. To delve into the interaction between KKCHFWPFPW and ACE, molecular docking simulations were conducted using the Maestro 2022-1 Glide software, shedding light on the inhibitory mechanism. This investigation suggests that peptides derived from the P. martensii pearl matrix hold promise as a novel source for antihypertensive agents.

Effects of fermentation with Lactiplantibacillus plantarum NCU116 on the antihypertensive activity and protein structure of black sesame seed

Effects of fermentation by Lactobacillus Plantarum NCU116 on the antihypertensive potential of black sesame seed (BSS) and structure characteristics of fermented black sesame seed protein (FBSSP) were investigated. Angiotensin-I-converting enzyme (ACE) inhibition and zinc chelating ability of fermented black sesame seed hydrolysate (FBSSH) reached the highest of 60.78 ± 3.67 % and 2.93 ± 0.04 mg/mL at 48 h and 60 h of fermentation, respectively. Additionally, the antioxidant activities of FBSSH and surface hydrophobicity of FBSSP were increased noticeably by fermentation. The α-helix and β-rotation of FBSSP tended to decrease and increase, respectively, during fermentation. Correlation analysis indicated strong positive relationships between β-turn and ACE inhibition activity as well as zinc chelating ability with correlation coefficients r of 0.8976 and 0.8932. Importantly, novel ACE inhibitory peptides LLLPYY (IC50 = 12.20 μM) and ALIPSF (IC50 = 558.99 μM) were screened from FBSSH at 48 h using in silico method. Both peptides showed high antioxidant activities in vitro. Molecular docking analysis demonstrated that the hydrogen bond connected with zinc ions of ACE mainly attributed to the potent ACE inhibitory activity of LLLPYY. The findings indicated that fermentation by Lactobacillus Plantarum NCU116 is an effective method to enhance the antihypertensive potential of BSS.

Identification of novel angiotensin converting enzyme (ACE) inhibitory peptides from Pacific saury: In vivo antihypertensive effect and transport route

Nature food-derived angiotensin converting enzyme inhibitory peptides (ACEIPs) can be potent and safe therapeutics for many medical illnesses, particularly hypertension. In this study, novel ACEIPs were screened and identified from Pacific saury by bio-activity guided approach through ultrafiltration membrane, Sephadex G-25 and RP-HPLC. The antihypertensive effect of ultrafiltration fraction was confirmed with spontaneous hypertensive rats' (SHRs) model. The peptides sequences of which gave the best activity was identified by Q-Orbitrap-MS/MS and selectively synthesized based on the binding energy of molecular docking. Five peptides VVLASLK, LTLK, LEPWR, ELPPK and LPTEK were synthesized, and the peptide LEPWR (IC50 = 99.5 μM) showed the best ACE inhibitory ability. Furthermore, LEPWR against ACE in a mixed competitive pattern and formed six hydrogen bonds with ACE. Additionally, the apparent permeability coefficient (Papp) of LEPWR was 3.56 ± 0.14 × 10-6 cm/s and paracellular transport across tight junctions was the main pathway across the Caco-2 monolayer. Therefore, the Pacific saury is a good material to prepare ACEIPs, but antihypertensive mechanism of peptide LEPWR on SHRs needs further investigation.

Discovery of ACE Inhibitory Peptides Derived from Green Coffee Using In Silico and In Vitro Methods

Inhibition of angiotensin-I converting enzyme (ACE) is an important means of treating hypertension since it plays an important regulatory function in the renin-angiotensin system. The aim of this study was to investigate the ACE inhibitory effect of bioactive peptides from green coffee beans using in silico and in vitro methods. Alcalase and thermolysin were employed to hydrolyze protein extract from coffee beans. Bioactive peptides were identified by LC-MS/MS analysis coupled with database searching. The potential bioactivities of peptides were predicted by in silico screening, among which five novel peptides may have ACE inhibitory activity. In vitro assay was carried out to determine the ACE inhibitory degree. Two peptides (IIPNEVY, ITPPVMLPP) were obtained with IC50 values of 57.54 and 40.37 μM, respectively. Furthermore, it was found that two inhibitors bound to the receptor protein on similar sites near the S1 active pocket of ACE to form stable enzyme-peptide complexes through molecular docking, and the Lineweaver-Burk plot showed that IIPNEVY was a noncompetitive inhibitor, and ITPPVMLPP was suggested to be a mixed-type inhibitor. Our study demonstrated that two peptides isolated from coffee have potential applications as antihypertensive agents.

Identification and application of species-specific peptide biomarkers from soft-shelled turtles (Pelodiscus sinensis) using post-translational modification detection-based peptidomics analysis

The soft-shelled turtle is a commercially aquatic species in Asian countries, which serves as an important source of collagen with high nutritional and medicinal value, so it is of great significance to distinguish soft-shelled turtle derived collagen from others or adulterations. In this work, peptidomics analysis based on post-translational modification (PTM) assay was used to discover specific peptide biomarkers of soft-shelled turtle gelatin (STG). In total eight specific sequences and 74 peptides with different PTM types were screened out, and seven peptides with good signal responses and STG specificity were selected and validated as STG-specific peptide biomarkers. These peptide biomarkers could be used for distinguishing STG from other animal gelatins, and applied for ensuring the quality of collagens or gelatins from soft-shelled turtle with authenticity and traceability.

Abalone Viscera Fermented with Aspergillus oryzae 001 Prevents Pressure Elevation by Inhibiting Angiotensin Converting Enzyme

Abalone viscera, which accounts for more than 20% of the total weight of abalone, is generally regarded as waste in the food industry, and effective methods are required to utilize it productively. In this study, the viscera were fermented with Aspergillus oryzae 001 to add functionality. Fermented abalone viscera exhibited increased angiotensin I-converting enzyme (ACE) inhibitory activity and enhanced inhibition of blood pressure elevation in spontaneously hypertensive rats (SHRs). Abalone viscera administration had no significant effect on body weight, food intake, liver and kidney weights, or serum components in SHRs. ACE inhibitors specific to fermented abalone viscera were identified through extraction, fractionation, purification, and analysis. The identified substance was L-m-tyrosine, which non-competitively inhibited ACE and, in a single oral administration, significantly reduced blood pressure in SHRs compared to that in the control. This study identified that abalone viscera fermented by A. oryzae 001 has an inhibitory effect on blood pressure elevation, suggesting its potential use as a functional food. In addition, L-m-tyrosine, a unique substance in fermented abalone viscera, was isolated for the first time as a single ACE-inhibitory amino acid.

Exploration of interaction between angiotensin I-converting enzyme (ACE) and the inhibitory peptide from Wakame (Undaria pinnatifida)

The interaction between angiotensin I-converting enzyme (ACE) and the inhibitory peptide KNFL from Wakame was explored using isothermal titration calorimetry, multiple spectroscopic techniques and molecular dynamics simulations, and an inhibition model was established based on free energy binding theory. The experiments revealed that the binding of KNFL to ACE was a spontaneous exothermic process driven by enthalpy and entropy and occurred via multiple binding sites to form stable complexes. The complexes may be formed through multiple steps of inducing fit and conformational selection. The peptide KNFL had a fluorescence quenching effect on ACE and its addition not only affected the microenvironment around the ACE Trp and Tyr residues, but also increased the diameter and altered the conformation of ACE. This study should prove useful for improving our understanding of the mechanism of ACE inhibitory peptides.

Seventeen novel angiotensin converting enzyme (ACE) inhibitory peptides from protein hydrolysate of Mytilus edulis: Isolation, identification, molecular docking study, and protective function on HUVECs

In the study, seventeen angiotensin converting enzyme (ACE) inhibitory peptides were isolated from protein hydrolysate of blue mussel (Mytilus edulis) and identified as MFR, MFV, FV, KP, QP, QVK, IK,...

A novel angiotensin-converting enzyme inhibitory peptide from rabbit meat protein hydrolysate: identification, molecular mechanism, and antihypertensive effect in vivo

Bioactive peptides exhibiting angiotensin-converting enzyme (ACE) inhibitory effects and extracted from natural foods have potential as healthy and safe therapeutics for high blood pressure. The aim of this study was to isolate and purify ACE inhibitory peptides from rabbit meat protein hydrolysate, to explore the underlying mechanisms by molecular docking, and to evaluate the antihypertensive effects in vivo. A novel ACE inhibitory tetrapeptide Trp-Gly-Ala-Pro (WGAP) was identified and purified from a bromelain hydrolysate. WGAP acted against ACE in a non-competitive manner with an IC₅₀ of 140.70 ± 4.51 μM. It was resistant to enzymatic degradation by pepsin and trypsin in vitro. Molecular docking analysis indicated that WGAP formed stable hydrogen bonds with ACE residues His353, Ala354 and ALA356. In vivo, 100 mg kg^-1 WGAP significantly reduced systolic and diastolic blood pressure in hypertensive rats by up to 42.66 ± 2.87 and 28.56 ± 2.71 mmHg, respectively, 4 h after oral administration. ACE inhibitory peptides derived from rabbit meat have potential antihypertensive effects and provide a new route for the exploration of novel hypertension inhibitors and the utilization of rabbit meat.

A Novel Angiotensin-I-Converting Enzyme (ACE) Inhibitory Peptide from Takifugu flavidus

Alcalase, neutral protease, and pepsin were used to hydrolyze the skin of Takifugu flavidus. The T. flavidus hydrolysates (TFHs) with the maximum degree of hydrolysis (DH) and angiotensin-I-converting enzyme (ACE)-inhibitory activity were selected and then ultra-filtered to obtain fractions with components of different molecular weights (MWs) (<1, 1-3, 3-10, 10-50, and >50 kDa). The components with MWs < 1 kDa showed the strongest ACE-inhibitory activity with a half-maximal inhibitory concentration (IC50) of 0.58 mg/mL. Purification and identification using semi-preparative liquid chromatography, Sephadex G-15 gel chromatography, RP-HPLC, and LC-MS/MS yielded one new potential ACE-inhibitory peptide, PPLLFAAL (non-competitive suppression mode; IC50 of 28 μmmol·L-1). Molecular docking and molecular dynamics simulations indicated that the peptides should bind well to ACE and interact with amino acid residues and the zinc ion at the ACE active site. Furthermore, a short-term assay of antihypertensive activity in spontaneously hypertensive rats (SHRs) revealed that PPLLFAAL could significantly decrease the systolic blood pressure (SBP) and diastolic blood pressure (DBP) of SHRs after intravenous administration. These results suggested that PPLLFAAL may have potential applications in functional foods or pharmaceuticals as an antihypertensive agent.

Inhibition effect of nicotinamide (vitamin B3) and reduced glutathione (GSH) peptide on angiotensin-converting enzyme activity purified from sheep kidney

Angiotensin-converting enzyme (ACE, EC 3.4.15.1) plays a significant role in blood pressure regulation and inhibition of this enzyme is one of the significant drug targets for the treatment of hypertension. In this work, ACE was purified from sheep kidneys with the affinity chromatography method in one step. The purity and molecular weight of ACE were designated using the SDS-PAGE method and observed two bands at around 60 kDa and 70 kDa on the gel. The effects of nicotinamide (vitamin B₃) and reduced glutathione (GSH) peptide on purified ACE were researched. Nicotinamide and GSH peptide on purified ACE showed an inhibition effect. IC₅₀ values for nicotinamide and GSH were calculated as 14.3 μM and 7.3 μM, respectively. Type of inhibition and K_i values for nicotinamide and GSH from the Lineweaver-Burk graph were determined. The type of inhibition for nicotinamide and GSH was determined as non-competitive inhibition. K_i value was calculated as 15.4 μM for nicotinamide and 6.7 μM for GSH. Also, GSH peptide showed higher inhibitory activity on ACE activity than nicotinamide. In this study, it was concluded that nicotinamide and GSH peptide compounds, which show an inhibition effect on ACE activity, may have both protective and therapeutic effects against hypertension.

Angiotensin I-converting enzyme inhibitory peptide: an emerging candidate for vascular dysfunction therapy

Abnormal vasoconstriction, inflammation, and vascular remodeling can be promoted by angiotensin II (Ang II) in the renin-angiotensin system (RAS), leading to vascular dysfunction diseases such as hypertension and atherosclerosis. Researchers have recently focused on angiotensin I-converting enzyme inhibitory peptides (ACEIPs), that have desirable efficacy in vascular dysfunction therapy due to Ang II reduction by inhibiting ACE activity. Promising methods for the large-scale preparation of ACEIPs include selective enzymatic hydrolysis and microbial fermentation. Thus far, ACEIPs have been widely reported to be hydrolyzed from protein-rich sources, including animals, plants, and marine organisms, while many emerging microorganism-derived ACEIPs are theoretically biosynthesized through the nonribosomal peptide synthase (NRPS) pathway. Notably, vasodilatation, anti-inflammation, and vascular reconstruction reversal of ACEIPs are strongly correlated. However, the related molecular mechanisms underlying signal transduction regulation in vivo remain unclear. We provide a comprehensive update of the ACE-Ang II-G protein-coupled type 1 angiotensin receptor (AT1R) axis signaling and its functional significance for potential translation into therapeutic strategies, particularly targeting AT1R by ACEIPs, as well as specific related signaling pathways. Future studies are expected to verify the biosynthetic regulatory mechanism of ACEIPs via the NRPS pathway, the effect of gut microbiota metabolism on vascular dysfunction and rigorous studies of ACE-Ang II-AT1R signaling pathways mediated by ACEIPs in large animals and humans.

Screening and mechanisms of novel angiotensin-I-converting enzyme inhibitory peptides from rabbit meat proteins: A combined in silico and in vitro study

Bioactive peptides derived from food proteins have various physiological roles and have attracted increasing attention in recent years. In this study, two novel ACE inhibitory peptides (EACF and CDF), screened from rabbit meat proteins using in silico methods, exhibited strong inhibitory effects in vitro. EACF and CDF were competitive and non-competitive inhibitors with half-maximal inhibitory concentrations of 41.06 ± 0.82 µM and 192.17 ± 2.46 µM, respectively. Molecular docking experiments revealed that EACF established eight H-bond interactions in the S1 and S2 pockets, and a metal-acceptor interaction with Zn 701. CDF shared four H-bond interactions in the S1 pocket of ACE. The results suggested that rabbit meat proteins could be a suitable material for the preparation of ACE inhibitory peptides, and that virtual screening is an effective, accurate and promising method for the discovery of novel active peptides.

Nutritional composition and proteomic analysis of soft-shelled turtle (Pelodiscus sinensis) egg and identification of oligopeptides with alpha-glucosidase inhibitory activity

This study aimed to explore nutritional compositions and proteomics of soft-shelled turtle (SST) egg, as well as identify potential antidiabetic oligopeptides with α-glucosidase inhibitory property. Results revealed that SST egg is a promising source of highly nutritious proteins and minerals (54.64% and 5.81% of dry matter, respectively). Further proteomic analysis showed SST egg proteins contained at least 9 protein families, such as transferrin/iron binding protein and immunoregulation-related protein. Hydrolysis by different enzymes, especially papain, remarkably increased α-glucosidase inhibitory activity and scavenging activity for ABTS, DPPH, hydroxyl and oxygen radicals of SST egg proteins. Peptides from papain hydrolysate were fractionated using ultrafiltration followed by reverse phase chromatography, and 16 peptides were identified in the most active fraction by LC-QTOF-MS/MS. Molecular docking revealed that 14 of these peptides could easily dock into the substrate-binding pocket and/or inhibitor binding sites of α-glucosidase with the docking score below -150 kcal/mol, indicating their potential α-glucosidase inhibitory properties. The five most abundant oligopeptides with potent interaction with α-glucosidase were further synthesized, and oligopeptides HNKPEVEVR, ARDASVLK and SGTLLHK strongly inhibited the activity of α-glucosidase (IC₅₀ of 56, 195 and 289 µmol/L, respectively). Therefore, oligopeptides from enzymatic hydrolysate of SST egg protein exhibit potential antidiabetic activity, making it a promising functional food ingredient.

The immunomodulatory effects of Carapax Trionycis ultrafine powder on cyclophosphamide-induced immunosuppression in Balb/c mice

BACKGROUND

There are abundant resources of Carapax Trionycis from soft-shelled turtle processing wastes each year in China. Our preliminary work showed that Carapax Trionycis ultrafine powder (CTUP) obtained using ball-milling with a particle size of 2.24 μm (D0.025) contained more active ingredients. The CTUP D0.025 has a good bioaccessibility, but there has been no report about the immunomodulatory function of CTUP. Therefore, using a cyclophosphamide-induced immunosuppression mice model, we investigated the immunomodulatory effects of CTUP D0.025.

RESULTS

The results indicated that CTUP D0.025 administration significantly improved the immune organ (bone marrow, thymus and spleen) indices, ameliorated spleen tissue morphology and increased the capacity of splenocyte proliferation and the activity of macrophage phagocytosis. CTUP D0.025 also significantly promoted the secretion of cytokines (IL-2, IL-4, IL-10, IFN-γ and TNF-α), improved the related mRNA expression levels of IL2, IFN-γ, T-bet and GATA3 in immunosuppressed mice and increased the production of serum hemolysin and the levels of IgG, IgM as well as complement C₃ . Moreover, CTUP D0.025 administration enhanced the antioxidant capacity of mice, exhibited a moderating effect on the damage of bone and skeletal muscle and improved the recovery of bone mineral density and calcium metabolism.

CONCLUSIONS

These findings demonstrated that CTUP D0.025 had an effective immune-enhancing function in immunosuppressive Balb/c mice and also exhibited anti-osteoporosis properties. © 2020 Society of Chemical Industry.

Affinity Purification of Angiotensin Converting Enzyme Inhibitory Peptides from Wakame (Undaria Pinnatifida) Using Immobilized ACE on Magnetic Metal Organic Frameworks

Angiotensin-I-converting enzyme (ACE) inhibitory peptides derived from marine organism have shown a blood pressure lowering effect with no side effects. A new affinity medium of Fe3O4@ZIF-90 immobilized ACE (Fe3O4@ZIF-90-ACE) was prepared and used in the purification of ACE inhibitory peptides from Wakame (Undaria pinnatifida) protein hydrolysate (<5 kDa). The Fe3O4@ZIF-90 nanoparticles were prepared by a one-pot synthesis and crude ACE extract from pig lung was immobilized onto it, which exhibited excellent stability and reusability. A novel ACE inhibitory peptide, KNFL (inhibitory concentration 50, IC50 = 225.87 μM) was identified by affinity purification using Fe3O4@ZIF-90-ACE combined with reverse phase-high performance liquid chromatography (RP-HPLC) and MALDI-TOF mass spectrometry. Lineweaver-Burk analysis confirmed the non-competitive inhibition pattern of KNFL, and molecular docking showed that it bound at a non-active site of ACE via hydrogen bonds. This demonstrates that affinity purification using Fe3O4@ZIF-90-ACE is a highly efficient method for separating ACE inhibitory peptides from complex protein mixtures and the purified peptide KNFL could be developed as a functional food ingredients against hypertension.

Interaction with longan seed polyphenols affects the structure and digestion properties of maize starch

This study investigated effects of longan seed polyphenols (LSPs) on the structure and digestion properties of starch, and discussed the interaction mechanism between starch and LSPs. The results showed cooking with 20 % LSPs did not change amylopectin chain length distribution of normal maize starch, however, the amylose content was reduced from 21.60 to 14.03 %. This suggests LSPs may interact with starch via non-covalent bond. Isothermal titration microcalorimetry and XRD results confirmed the existence of non-covalent interaction, and indicated that LSPs may enter the hydrophobic cavity of amylose, forming V-type inclusion complex. LSPs did not affect gelatinization temperatures of maize starch, whereas 20 % LSPs decreased the enthalpy change by about 26 %. The digestion results indicate significant inhibition effect of LSPs on the digestion of cooked starch, attributing to the interaction of LSPs with starch. These suggest potential applications of LSPs as functional ingredients in modulating postprandial glycemic response of starchy food.

Bioavailability and prebiotic potential of Carapax Trionycis, a waste from soft-shelled turtle processing

BACKGROUND

Carapax Trionycis is the shell of the soft-shelled turtle. It is rich in minerals, amino acid, peptides, and other nutrients. Current processing and consumption of soft-shelled turtle leads to the waste of huge quantities of Carapax Trionycis in the form of spent materials. In this study, the bioavailability, prebiotic activity, and physicochemical properties of Carapax Trionycis using different processing methods were investigated. The vinegar-quenched Carapax Trionycis (V-CT), fine powders (D0.18, D0.10), and superfine powders (D0.05, D0.025) of Carapax Trionycis were prepared by the vinegar-quenching method, common grinding, and the superfine grinding method.

RESULTS

The average particle sizes of D0.18, D0.10, D0.05, and D0.025 were 147.82, 77.35, 36.65, and 2.24 μm, respectively. Superfine grinding changed the surface morphology of Carapax Trionycis and promoted the release of active ingredients. D0.025 had the highest polypeptide (8.15%), polysaccharide (1.21%), total free amino acid (232.36 mg 100 g^-1 ) and water-soluble extract content (10.74%), and showed the highest calcium release rate (55.64%) after in vitro digestion. The apparent permeability (P_APP ) of the resulting Carapax Trionycis samples in the dialysis tubing model and the everted intestinal sac model increased significantly with the decrease in the Carapax Trionycis particle sizes. Furthermore, the five Carapax Trionycis samples significantly stimulated the growth of the tested probiotics and increased lactic acids production after 48 h fermentation compared to the control. The Carapax Trionycis powder prepared by superfine grinding displayed better prebiotic activity than other samples as it significantly induced a greater proliferation of probiotic bacteria and higher production of lactic acid, as well as greater release of free calcium.

CONCLUSIONS

The results showed that Carapax Trionycis superfine powder D0.025 had the highest active ingredient content, calcium bioavailability, and prebiotic activity. Our approach of developing Carapax Trionycis superfine powder as natural calcium supplement or potential prebiotic would therefore broaden the scope of soft-shelled turtle processing waste utilization in an eco-friendly, cost-effective, and sustainable approach in the future. © 2020 Society of Chemical Industry.

Effect of Different Proteases on the Degree of Hydrolysis and Angiotensin I-Converting Enzyme-Inhibitory Activity in Goat and Cow Milk

Angiotensin I-converting enzyme (ACE) peptides are bioactive peptides that have important value in terms of research and application in the prevention and treatment of hypertension. While widespread literature is concentrated on casein or whey protein for production of ACE-inhibitory peptides, relatively little information is available on selecting the proper proteases to hydrolyze the protein. In this study, skimmed cow and goat milk were hydrolyzed by four commercial proteases, including alkaline protease, trypsin, bromelain, and papain. Angiotensin I-converting enzyme-inhibitory peptides and degree of hydrolysis (DH) of hydrolysates were measured. Moreover, we compared the difference in ACE-inhibitory activity between cow and goat milk. The results indicated that the DH increased with the increase in hydrolysis time. The alkaline protease-treated hydrolysates exhibited the highest DH value and ACE-inhibitory activity. Additionally, the ACE-inhibitory activity of hydrolysates from goat milk was higher than that of cow milk-derived hydrolysates. Therefore, goat milk is a good source to obtain bioactive peptides with ACE-inhibitory activity, as compared with cow milk. A proper enzyme to produce ACE-inhibitory peptides is important for the development of functional milk products and will provide the theoretical basis for industrial production.