Primary and secondary structure of novel ACE-inhibitory peptides from egg white protein

Effects on functional groups and zeta potential of SAP1<MW<3kDa treated by pulsed electric field technology

BACKGROUND

SAP_1<MW<3kDa was chosen to investigate the improvement of antioxidant activity of peptides treated with pulsed electric field (PEF) technology. The effects of electric field intensity and pulse frequency on SAP_1<MW<3kDa were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition, as well as the zeta potential and functional groups.

RESULTS

One-factor-at-a-time tests indicated that the PEF-treated sample had the strongest antioxidant activity (P < 0.05) and the lowest zeta potential value. The increase of antioxidant activity of SAP_1<MW<3kDa may be attributed to a loss of C = C and the amide band. Using a response surface methodology (RSM) experiment, it was shown that DPPH radical inhibition of SAP_1<MW<3kDa increased to 90.22 ± 0.90% at the optimal conditions (electric field intensity 15 kV cm^-1 , pulse frequency 1600 Hz and flow velocity 2.93 mL min^-1 ). Furthermore, the PEF-treated SAP_1<MW<3kDa under optimal conditions lacked the characteristic absorbance of N-H, C = C and the amide band and the zeta potential was reduced to -18.0 mV.

CONCLUSION

Overall, the results of the present study suggest that the improvement of antioxidant activity of SAP_1<MW<3kDa is a result of the contribution of the functional groups and the change in zeta potential when treated with PEF. © 2016 Society of Chemical Industry.

Egg-derived bioactive peptides with ACE-inhibitory properties: a literature update

Egg proteins contain a wide set of peptide sequences which have an impact on cardiovascular health.

Effect of pulsed electric field (PEF) on structures and antioxidant activity of soybean source peptides-SHCMN

Recently, high-intensity pulsed electric field (PEF) has successfully used in improvement of antioxidant activity. Ser-His-Cys-Met-Asn (SHCMN) obtained from soybean protein was chosen to investigate the phenomenon of antioxidant activity improvement. Effects of PEF treatment on antioxidant activity of SHCMN were evaluated by DPPH radical inhibition. Nuclear magnetic resonance (NMR), mid-infrared (MIR), circular dichroism (CD) were used to analyze structures of SHCMN. Two-factor-at-a-time results show that DPPH radical inhibition of SHCMN is significantly (P<0.05) increased to 94.35±0.03% at conditions of electric field intensity of 5kV/cm, pulse frequency of 2400Hz, and retention time of 2h. In addition, MIR and NMR spectra show that the basic structure of peptides SHCMN is stable by PEF treatment. But the secondary structures (α-helix, β-turn, and random coil) can be affected and zeta potential of PEF-treated SHCNM was reduced to 0.59±0.03mV. The antioxidant activity improvement of SHCMN might result from the changes of secondary structures and zeta potential.

Anxiolytic effects of ACE inhibitory peptides on the behavior of rats in an elevated plus-maze

Three novel egg white-derived peptides were demonstrated to display in vitro activities against the angiotensin converting enzyme (ACE).

Enzymatic hydrolysis of ovomucoid and the functional properties of its hydrolysates

Ovomucoid is well known as a "trypsin inhibitor" and is considered to be the main food allergen in egg. However, the negative functions of ovomucoid can be eliminated if the protein is cut into small peptides. The objectives of this study were to hydrolyze ovomucoid using various enzyme combinations, and compare the functional properties of the hydrolysates. Purified ovomucoid was dissolved in distilled water (20 mg/mL) and treated with 1% of pepsin, α-chymotrypsin, papain, and alcalase, singly or in combinations. Sodium sodium dodecyl sulfate-polyacrylamide (SDS-PAGE) results of the hydrolysates indicated that pepsin (OMP), alcalase (OMAl), alcalase+trypsin (OMAlTr), and alcalase+papain (OMAlPa) treatments best hydrolyzed the ovomucoid, and the 4 treatments were selected to determine their functional characteristics. Among the 4 enzyme treatments, hydrolysate from OMAlTr showed the highest iron-chelating and antioxidant activities, while OMP showed higher ACE-inhibitory activity, but lower Fe-chelating activity than the other treatments. However, no difference in the copper-chelating activity among the treatments was found. MS/MS analysis identified numerous peptides from the hydrolysates of OMAlPa and OMAlTr, and majority of the peptides produced were <2 kDa. Pepsin treatment (OMP), however, hydrolyzed ovomucoid almost completely and produced only amino acid monomers, di- and tri-peptides. The ACE-inhibitory, antioxidant and iron-chelating activities of the enzyme hydrolysates were not consistent with the number and size of peptides in the hydrolysates, but we do not have information about the quantity of each peptide present in the hydrolysates at this point.

Activity prediction and molecular mechanism of bovine blood derived angiotensin I-converting enzyme inhibitory peptides

Development of angiotensin I-converting enzyme (ACE, EC 3.4.15.1) inhibitory peptides from food protein is under extensive research as alternative for the prevention of hypertension. However, it is difficult to identify peptides released from food sources. To accelerate the progress of peptide identification, a three layer back propagation neural network model was established to predict the ACE-inhibitory activity of pentapeptides derived from bovine hemoglobin by simulated enzyme digestion. The pentapeptide WTQRF has the best predicted value with experimental IC50 23.93 μM. The potential molecular mechanism of the WTQRF / ACE interaction was investigated by flexible docking.

Multifunctional peptides derived from an egg yolk protein hydrolysate: isolation and characterization

An egg yolk protein by-product following ethanol extraction of phospholipids (YP) was hydrolyzed with pepsin to produce and identify novel peptides that revealed antioxidant, ACE inhibitory and antidiabetic (α-glucosidase and DPP-IV inhibitory) activities. The peptic hydrolysate of YP was fractionated by ion-exchange chromatography and reversed-phase high-pressure liquid chromatography. Isolated peptides were identified using mass spectrometry (MALDI-ToF) and the Mascot Search Results database. Four peptides of MW ranging from 1,210.62 to 1,677.88 Da corresponded to the fragments of Apolipoprotein B (YINQMPQKSRE; YINQMPQKSREA), Vitellogenin-2 (VTGRFAGHPAAQ) and Apovitellenin-1 (YIEAVNKVSPRAGQF). These peptides were chemically synthesized and showed antioxidant, ACE inhibitory or/and antidiabetic activities. Peptide YIEAVNKVSPRAGQF exerted the strongest ACE inhibitory activity, with IC₅₀ = 9.4 µg/mL. The peptide YINQMPQKSRE showed the strongest DPPH free radical scavenging and DPP-IV inhibitory activities and its ACE inhibitory activity (IC₅₀) reached 10.1 µg/mL. The peptide VTGRFAGHPAAQ revealed the highest α-glucosidase inhibitory activity (IC₅₀ = 365.4 µg/mL). A novel nutraceutical effect for peptides from an egg yolk hydrolysate was shown.

Transport of Egg White ACE-Inhibitory Peptide, Gln-Ile-Gly-Leu-Phe, in Human Intestinal Caco-2 Cell Monolayers with Cytoprotective Effect

The purpose of this study was to investigate the transepithelial transport and cytoprotective effect of Gln-Ile-Gly-Leu-Phe (QIGLF), an ACE-inhibitory peptide derived from egg white ovalbumin, in human intestinal Caco-2 cell monolayers. The results showed that QIGLF could be absorbed intact through Caco-2 cell monolayers with a P_app value of (9.11 ± 0.19) × 10^-7 cm/s (transport kinetic parameters: K_m, 32.37 ± 12.59 mM; V_max, 1.23 ± 0.49 μM/min cm²). The transport was not significantly decreased by sodium azide and Gly-Pro, an ATP synthesis inhibitor and a peptide transporter 1 (PepT1) substrate, respectively, suggesting that transport of QIGLF was not energy-dependent and carrier-mediated. In addition, wortmannin, a transcytosis inhibitor, had little effect on the transport, suggesting that endocytosis was not involved in the transport of QIGLF. However, the transport of QIGLF was increased significantly in the presence of cytochalasin D, a tight junction disruptor, suggesting that paracellular transport via tight junctions was the major transport mechanism for intact QIGLF across Caco-2 cell monolayers. Moreover, QIGLF was added to Caco-2 cells followed by addition of H₂O₂, and exhibited significant cytoprotective effect in Caco-2 cells against oxidative stress induced by H₂O₂.

Egg white proteins and their potential use in food processing or as nutraceutical and pharmaceutical agents--a review

Egg white contains many functionally important proteins. Ovalbumin (54%), ovotransferrin (12%), ovomucoid (11%), ovomucin (3.5%), and lysozyme (3.5%) are among the major proteins that have high potentials for industrial applications if separated. The separation methods for these proteins from egg white have been developed since early 1900, but preparation methods of these proteins for commercial applications are still under development. Simplicity and scalability of the methods, use of nontoxic chemicals for the separation, and sequential separation for multiple proteins are very important criteria for the commercial production and application of these proteins. The separated proteins can be used in food and pharmaceutical industry as is or after modifications with enzymes. Ovotransferrin is used as a metal transporter, antimicrobial, or anticancer agent, whereas lysozyme is mainly used as a food preservative. Ovalbumin is widely used as a nutrient supplement and ovomucin as a tumor suppression agent. Ovomucoid is the major egg allergen but can inhibit the growth of tumors, and thus can be used as an anticancer agent. Hydrolyzed peptides from these proteins showed very good angiotensin I converting enzyme inhibitory, anticancer, metal binding, and antioxidant activities. Therefore, separation of egg white proteins and the productions of bioactive peptides from egg white proteins are emerging areas with many new applications.

Development of a high-performance liquid chromatography-electrospray ionization-quadrupole-time-of-flight-mass spectrometry methodology for the determination of three highly antihypertensive peptides in maize crops

The simultaneous quantification of three highly antihypertensive peptides (LRP, LSP, and LQP) in six maize crops using novel HPLC-ESI-Q-ToF methodology is presented. The method included the extraction of α-zein proteins from maize, their purification by acetone precipitation, digestion with thermolysin and HPLC separation in a fused-core column. Several MS parameters were optimized to increase sensitivity and reduce spontaneous fragmentation of peptide ions into the ESI source. The ions with m/z 193.1315, 385.2558 (for LRP), 316.1867 (for LSP), and 357.2132 (for LQP) were monitored in the optimization and characterization of the method. In order to improve the repeatability, sensitivity, and the stability of peptides in the sample, the removal of urea was required. The use of two solid-phase extraction methods to remove urea from digested extract was evaluated. For the first time filter-aided sample preparation approach for the study of bioactive peptides in foodstuffs has been proposed. The optimized HPLC-ESI-Q-ToF method was characterized by the evaluation of linearity, LOD, LOQ, precision, and recovery. A study on the existence of matrix interferences was also performed. The developed method was applied to the quantification of LRP, LQP, and LSP peptides in maize lines using the standard addition method. The results showed the highest yield of LSP peptide in EZ11A line and LRP and LQP peptides in A632 line.

Identification of pyrroloindoline-containing cyclic hexapeptides in the metabolites of Streptomyces alboflavus 313 by HPLC-DAD-ESI-MS/MS

To investigate the chemical biodiversity of biologically active cyclic hexapeptides in the metabolites from microorganisms, the fermentation broth of Streptomyces alboflavus 313 was analyzed using HPLC, equipped with a diode array detector (DAD), coupled with ESI tandem MS (HPLC-DAD-ESI-MS/MS). In the mass spectra of cyclic hexapeptides, predominant ions [M+H](+), as well as [M-18+H](+), [M-28+H](+) and [M+Na](+), were observed and used to determine the molecular masses, while fragmentation reactions of [M+H](+) were recorded to provide information on the contents of amino acids and their linkage sequence. Based on the fragmentation patterns and comparison with standards, 15 pyrroloindoline-containing natural cyclic hexapeptides, cp01-15, were identified from the microorganism and six of these are reported for the first time.