Identification of novel angiotensin I-converting enzyme inhibitory peptide from collagen hydrolysates and its molecular inhibitory mechanism

The fish collagen protein was hydrolysed and further fractionated into four molecular weight ranges by ultrafiltration. Subsequently, the peptide fraction with the potent angiotensin I-converting enzyme (ACE) inhibitory activity was identified. The potential inhibitory mechanism of the peptide was clarified by molecular docking. As a result, FCPH-Ⅳ with molecular weight between 600 and 1000 Da exerted the high ACE inhibitory activity and was identified by de novo peptide sequencing. The peptide GHVGAAGS exhibited significant ACE inhibitory activity with the IC₅₀ value of 407.28 ± 3.55 μm . In addition, the docking results showed the interactions between the amino acids at the four positions closest to the C-terminal site of GHVGAAGS and the major active residues (GLN281, HIS353, LYS511 and HIS513) of ACE lead to the conformational change in ACE. This work indicates that fish collagen could be utilised to produce ACE inhibitory peptides and develop health products.     

Development of a salmon protein hydrolysate that lowers blood pressure

A salmon protein hydrolysate (SPH) was developed containing several angiotensin I-converting enzyme (ACE) inhibitory tripeptides the most abundant of which were Val-Leu-Trp, Val-Phe-Tyr, and Leu-Ala-Phe. Simulated digestion experiments showed that active constituents of SPH would survive in the digestive tract and be available for absorption into the bloodstream. In fact, ACE inhibitory activity was improved following simulated digestion suggesting that there were larger peptides in SPH that might contribute to bioactivity in vivo. A single oral dose (1,500 mg/kg body mass) of SPH significantly lowered blood pressure in spontaneously hypertensive rats (SHR). The treatment of SHR with either SPH fraction (<3,000 Da) or SPH fraction (>3,000 Da) reduced blood pressure. We conclude that the ability of SPH to lower blood pressure is due to a combination of ACE inhibitory tripeptides as identified, as well as additional unknown, peptide species that are generated during digestion of SPH in the gastrointestinal tract.     

Novel angiotensin I-converting enzyme inhibitory peptide derived from bovine casein

Bovine lactic casein was hydrolysed using a combination of three enzymes, namely, subtilisin, bacillolysin, and trypsin, and the resulting preparation was coined CH-3. CH-3 showed angiotensin I-converting enzyme (ACE)-inhibitory activity (IC₅₀: 74 μg/mL). A single oral administration of CH-3 led to a transient but significant decrease in the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHRs), while daily oral administration of CH-3 for 28 consecutive days led to a lower rate of SBP increase. The CH-3 preparation was then fractionated and the _αS2-casein-derived tripeptide Met-Lys-Pro (or MKP) was identified as a novel peptide with strong ACE-inhibitory activity (IC₅₀ = 0.12 μg/mL, 0.3 μM). The MKP peptide constituted only 0.053% of CH-3 but its activity was accounted for 33% of the total ACE-inhibitory activity of CH-3. In addition, a single oral administration of MKP also led to a transient but significant decrease in the SBP of SHRs.     

Identification of angiotensin I-converting enzyme inhibitory peptides from koumiss, a traditional fermented mare's milk

Angiotensin I-converting enzyme (ACE) inhibitory activities in untreated koumiss and koumiss digested with ACE, pepsin, trypsinase, and chymotrypsin were compared and analyzed. Four novel ACE inhibitory peptides (P_I, P_K, P_M, and P_P) were purified using ultrafiltration and high performance liquid chromatography (HPLC). The classification study showed that these 4 peptides were of the true inhibitor type. The amino acid sequences of these peptides are YQDPRLGPTGELDPATQPIVAVHNPVIV, PKDLREN, LLLAHLL, and NHRNRMMDHVH, respectively. Their individual IC₅₀ (50% inhibitory concentration) values were as follows: 14.53 ± 0.21 μM, 9.82 ± 0.37 μM, 5.19 ± 0.18 μM, and 13.42 ± 0.17 μM. From sequence analysis, we determined that P_I was part of β-casein in mare's milk. The 3 peptides P_K, P_M, and P_P did not correspond with any known milk protein. The results suggest that koumiss is rich in ACE inhibitory peptides, and the ACE inhibitors in koumiss are of the pro-drug type or a mixture of the pro-drug type and the true inhibitor type. These results may provide evidence about the beneficial effects of koumiss, especially on cardiovascular health.     

Novel angiotensin I-converting enzyme inhibitory peptides derived from soya milk

Inhibitors of angiotensin I-converting enzyme (ACE) are useful in treating hypertension, and many have been derived from food products, including soybeans. Using the industrial protease PROTIN SD-NY10, we developed a processed soya milk (PSM) with enhanced ACE inhibitory activity. The ACE inhibitory activity of PSM (IC₅₀ = 0.26 μg/ml) was greater than that of regular soya milk (IC₅₀ = 8.75 μg/ml). Eight novel ACE inhibitory peptides were purified from PSM by reversed-phase chromatography: FFYY (IC₅₀,1.9 μM), WHP (4.8 μM), FVP (10.1 μM), LHPGDAQR (10.3 μM), IAV (27.0 μM), VNP (32.5 μM), LEPP (100.1 μM), and WNPR (880.0 μM). The IC₅₀ values of these peptides are comparable to those reported for other ACE inhibitory peptides derived from wheat, chicken, bonito, wine, etc. Due to the relatively low IC₅₀ values of several peptides identified in this study, they may serve as ideal base components of food supplements for patients with hypertension.     

合成二肽ACE抑制活性及抗高血压初步研究

目的:对合成二肽的ACE抑制活性进行系统地筛选,寻找具有高ACE抑制活性的二肽并研究其在动物体内的降血压作用。方法:利用可见光分光光度法对35种合成二肽的ACE抑制活性进行测定,并对具有高ACE抑制活性的二肽进一步测定其IC50值。选取ACE抑制效果最佳的二肽进行原发性高血压大鼠（SHR）降血压实验。实验采用灌胃方法分别以1、10、25、50、100 mg/kg的剂量溶于1 m L生理盐水进行给药,分别于给药后2 h和4 h测量大鼠血压变化。结果:研究发现大部分二肽都具有一定程度的ACE抑制活性,其中以氨基酸序列为半胱氨酸-丙氨酸（Cys-Ala,CA）和半胱氨酸-组氨酸（CysHis,CH）的二肽ACE抑制活性最高,其ACE抑制率分别达到84.38%和70.79%。经测定CA和CH的IC50值分别为23.22μmol/L和61.17μmol/L。SHR大鼠降血压实验表明CA在体内的降压效果显著。给药后4 h CA降压效果优于给药后2 h,给药后2 h CA降压效果与给药剂量呈较好的正相关性（R2>0.8）。结论:体外ACE抑制率测定及SHR大鼠降血压实验发现合成二肽CA具有较高的ACE抑制活性和较好的体内降血压效果,提示CA可以作为降血压保健食品的添加成分,值得进一步研究。      

胃蛋白酶水解甘薯蛋白制备血管紧张素转化酶抑制肽的研究

采用胃蛋白酶水解甘薯蛋白制备血管紧张素转化酶(ACE)抑制肽,通过四元二次回归正交旋转组合设计,考察底物浓度、酶与底物浓度比、pH值、温度对ACE抑制率的影响,并确定最优酶解工艺参数,最终建立了ACE抑制率与各影响因素的回归模型。在此基础上,确定了胃蛋白酶水解甘薯蛋白的最适条件为:底物浓度2.3%、酶与底物浓度比3.7%、pH2.3、温度37℃、时间8h,采用该优化工艺,得到ACE抑制率最大为78.37%的水解产物。为开发防治高血压的保健食品提供了理论依据。     

源于食品蛋白质的血管紧张素Ⅰ转换酶抑制肽

血管紧张素I转换酶(ACE)是一种重要的血压调节因子,该酶的一些抑制剂有较好的降压效果,并作为预防和治疗高血压的食品和药物被广泛地使用。本文对不同食品来源的ACE抑制肽降压机理、结构和功能关系、应用前景进行了概述。     

Hypotensive effect of a sweetpotato protein digest in spontaneously hypertensive rats and purification of angiotensin I-converting enzyme inhibitory peptides

We have investigated angiotensin I-converting enzyme (ACE) inhibitory activity in an enzyme digest of sweetpotato protein, the antihypertensive effect of the digest in spontaneously hypertensive rats (SHR), and the identification of an ACE inhibitory peptide. Protein was prepared from squeezed juice of sweetpotato by isoelectric focusing precipitation. Three kinds of proteases were selected for effective protein digestion. The digest, sweetpotato peptide (SPP), exhibited strong ACE inhibitory activity (IC₅₀: 18.2 μg/ml). SPP was orally administered by gavage to SHR at a dose of 100 mg/kg or 500 mg/kg. The systolic blood pressure and the diastolic blood pressure were measured at 0 (before administration), 2, 4, 8, and 24 h after administration. A dose-dependent decrease in systolic blood pressure in SHR was observed after oral administration of SPP. Significant differences between SPP-administered rats and control rats were observed 4 and 8 h after administration in the 500 mg/kg-administered group and 8 h after administration in the 100 mg/kg-administered group. Diastolic blood pressure also decreased in the SPP-administered groups, although the difference between SPP-administered rats and control rats was not significant. These results suggest that SPP may be useful in the prevention or treatment of hypertension. Peptides with ACE inhibitory activity were purified from SPP by absorption chromatography and preparative HPLC using an ODS column. The amino acid sequences of isolated peptides were I-T-P, I-I-P, G-Q-Y and S-T-Y-Q-T; their ACE inhibitory activities (IC₅₀) were 9.5 μM, 80.8 μM, 52.3 μM and 300.4 μM, respectively. In conclusion, I-T-P is a novel, strong ACE inhibitory peptide.     

Tyr-Pro-Lys,an angiotensin I-converting enzyme inhibitory peptide derived from broccoli (Brassica oleracea Italica)

To investigate the naturally occurring angiotensin I-converting enzyme (ACE) inhibitor, broccoli (Brassica oleracea Italica) extracts were used for its isolation and identification. After treatment with 50% acetone for membrane breakdown, ethyl acetate, n-butanol, and water were used for the preparation of broccoli extracts. The water-soluble extract from broccoli had 76.9% ACE inhibitory activity, while those of other organic solvent extracts showed lower ACE inhibitory activities. An ACE inhibitory peptide was isolated using column chromatographic methods including: Amberlite XAD-4, Sephadex LH-20, and high performance liquid chromatography. The purified ACE inhibitory peptide was identified to be a tripeptide, Tyr-Pro-Lys, having an IC₅₀ value of 10.5 μg protein/ml.