Peptide Hydrolysis Research Articles

Formylation facilitates the reduction of oxidized initiator methionines

Within a cell, protein-bound methionines can be chemically or enzymatically oxidized, and subsequently reduced by methionine sulfoxide reductases (Msrs). Methionine oxidation can result in structural damage or be the basis of functional regulation of enzymes. In addition to participating in redox reactions, methionines play an important role as the initiator residue of translated proteins where they are commonly modified at their α-amine group by formylation or acetylation. Here, we investigated how formylation and acetylation of initiator methionines impact their propensity for oxidation and reduction. We show that in vitro, N-terminal methionine residues are particularly prone to chemical oxidation and that their modification by formylation or acetylation greatly enhances their subsequent enzymatic reduction by MsrA and MsrB. Concordantly, in vivo ablation of methionyl-tRNA formyltransferase (MTF) in Escherichia coli increases the prevalence of oxidized methionines within synthesized proteins. We show that oxidation of formylated initiator methionines is detrimental in part because it obstructs their ensuing deformylation by peptide deformylase (PDF) and hydrolysis by methionyl aminopeptidase (MAP). Thus, by facilitating their reduction, formylation mitigates the misprocessing of oxidized initiator methionines.

Development, characterization, and comparison of chitosan microparticles as a carrier system for black bean protein hydrolysates with antioxidant capacity.

Peptides in black bean protein hydrolysates (BPHs) exert antioxidant capacity. However, peptides are prone to degradation during processing and digestion. Chitosan (Ch) can protect them and provide a delayed release. This work develops and compares two drying methods producing porous structured Ch microparticles (MPs) as carriers for antioxidant BPH. Ch gels were obtained by ionic gelation and dried by supercritical CO2 solvent displacement or fast-freeze-drying methods. The resulting aerogels and fast-freeze-dried MPs were structurally characterized, and their swelling and release profiles were obtained at pH 1.2 and 7.4. The antioxidant capacity of systems was determined by 2,2'-azino-bis(3-ethyl-benzthiazoline-6-sulphonic acid) (ABTS) and superoxide radical assays. The results showed BPH-Ch best complexation conditions occurring at a pH of 4.5 and a 4:1 BPH/Ch ratio. The particle size of the complex was 1047.6nm, and the entrapment efficiency and loading capacity were 28.2% and 54.3%, respectively. At pH 1.2 and 7.4, the release rate of BPH was lower in aerogel than in fast-freeze-dried MPs. Besides, entrapment BPH in Ch significantly reduced the ABTS antioxidant activity IC50 from 35.1µM Trolox equivalents (TE)/mg to 250.7 and 406.2µM TE/mg for Ch fast-freeze-dried and aerogels, respectively. Superoxide radical inhibition IC50 ranged from 74.6 to 92.9mM ascorbic acid equivalents/mg in the different samples. BPH-loaded aerogels presented lower specific surface area (94.7 vs. 138.6m2/g, p<0.05) and higher average pore size (26.4 vs. 19.8nm) than Ch aerogels. Ch aerogel is a promising carrier for delaying the release of common bean antioxidant peptides useful for developing functional foods. PRACTICAL APPLICATION: This novel system could act as an ingredient to incorporate antioxidant compounds in different formats to develop delayed-release nutraceuticals and functional foods, such as bakery, dairy products, or beverages. Along, antioxidant peptide-loaded aerogels could be used as a slow-release system for compounds acting as natural preserving antioxidants for food applications such as raw meat products or high-fat foods.

Substrate engagement by the intramembrane metalloprotease SpoIVFB

S2P intramembrane metalloproteases regulate diverse signaling pathways across all three domains of life. However, the mechanism by which S2P metalloproteases engage substrates and catalyze peptide hydrolysis within lipid membranes has remained elusive. Here we determine the cryo-EM structure of the S2P family intramembrane metalloprotease SpoIVFB from Bacillus subtilis bound to its native substrate Pro-σK. The structure and accompanying biochemical data demonstrate that SpoIVFB positions Pro-σK at the enzyme active site through a β-sheet augmentation mechanism, and reveal key interactions between Pro-σK and the interdomain linker connecting SpoIVFB transmembrane and CBS domains. The cryo-EM structure and molecular dynamics simulation reveal a plausible path for water to access the membrane-buried active site of SpoIVFB, and suggest a possible role of membrane lipids in facilitating substrate capture. These results provide key insight into how S2P intramembrane metalloproteases capture and position substrates for hydrolytic proteolysis within the hydrophobic interior of a lipid membrane.

Exploring novel antioxidant cyclic peptides in corn protein hydrolysate: Preparation, identification and molecular docking analysis

Antioxidant cyclic peptides were successfully identified from a corn protein hydrolysate. Hydrolysate by Alcalase + Flavourzyme showed the highest cyclic peptide purity (48.36 ± 1.81 %) and higher antioxidant activities compared with other hydrolysate. The success of peptide cyclization in hydrolysate was demonstrated by thermogravimetric analysis and thin-layer chromatography (TLC) analysis. Thermogravimetric analysis showed that the thermal stability of hydrolysate after cyclization was significantly increased, which was related to the formation of cyclic peptides. Peptides with molecular weight less than 1000 Da accounted for more than 80 % in hydrolysate after cyclization. After separation using gel silica chromatography and semi-preparative reverse phase high performance liquid chromatography (RP-HPLC), 22 novel antioxidant cyclic peptides were identified by ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF-MS) and orbitrap-tandem mass spectrometry (Orbitrap-MS/MS). Synthetic cyclic peptides with the same sequence were synthesized and characterized for their antioxidant activity. Molecular docking suggested that the free radical molecules could bind with the cyclic backbone and side chain of cyclic peptides through hydrogen bonding, hydrophobic interaction as well as electrostatic interaction. This study has important implications for the high-value utilization of corn protein and new cyclic peptides drugs or functional food development.

Effect of ultrasound and enzymatic pre-treatments on the profile of bioactive peptides of beef liver hydrolysates

The use of meat by-products as a potential source of protein hydrolysates rich in bioactive peptides is of growing interest to valorise these products and improve their sustainable use. This study aimed to evaluate the effect of different pre-treatments (hydrolysis with pepsin, ultrasounds, and ultrasounds-assisted pepsin hydrolysis) on the peptide profile and bioactivity of beef liver hydrolysed with flavourzyme. The pre-treatments with pepsin increased the degree of hydrolysis and generation of free amino acids in the liver hydrolysates, whereas the subsequent hydrolysis with flavourzyme influenced the molecular weight distribution of the peptides. Samples pre-treated with pepsin and ultrasounds-assisted pepsin hydrolysates showed the highest values of antioxidant and inhibitory activity of ACE-I, ECE-I, DPP-IV, and neprilysin enzymes, and therefore these hydrolysates were characterised to obtain the bioactive peptide profiles. A total of 995 peptides were identified by tandem mass spectrometry in the most active fractions separated by reversed-phase liquid chromatography, and 20 of them were predicted as potentially responsible for the observed bioactivities and subsequently characterised by in silico tools. These results evidenced the potential of hydrolysis pre-treatments with pepsin and ultrasounds-assisted pepsin to obtain beef liver hydrolysates rich in bioactive peptides that could exert multifunctional bioactivities such as antioxidant, antihypertensive, and antidiabetic, while giving added value to this meat by-product.

Investigation of blood pressure regulatory effect of bioactive peptides in complex enzyme-assisted hydrolysate from Paralichthys olivaceus

This study aimed to identify the bioactive peptides of protamex-pepsin hydrolysate obtained from Paralichthys olivaceus (POppH) and to investigate their potential vasorelaxation and blood pressure regulatory properties, both in vitro and in vivo. The effects of the peptides on endothelium-derived relaxing factors (EDRFs), such as nitric oxide and hydrogen sulfate levels, were analyzed in EA.hy926 cells, and the vasorelaxation-related PI3K/AKT/eNOS pathway activity was analyzed in EA. hy926 cells. An in vitro study revealed that POppH and leucine-glutamic acid-arginine (IER) peptide did not show any cytotoxic effects and significantly increased EDRF production via the regulation of vasorelaxation-associated PI3K/AKT/eNOS protein expression in EA.hy926 cells. An in vivo study suggested that oral administration of IER reduced systolic, diastolic, and mean arterial blood pressure in a spontaneously hypertensive rat model. The bioactive peptide IER derived from Paralichthys olivaceus could be used in the development of functional food products with blood pressure regulatory properties.

Sea conch (Rapana venosa) peptide hydrolysate regulates NF‐κB pathway and restores intestinal immune homeostasis in DSS‐induced colitis mice

AbstractInflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract. Sea conch peptide hydrolysate (CPH) was produced by enzymatic digestion of fresh conch meat with trypsin enzyme. To analyze the molecular composition, functional groups, and structural morphology of the hydrolysate, we employed liquid chromatography–mass spectrometry (LC–MS), Fourier‐transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Results confirmed that crude protein could be effectively digested by enzymes to generate peptides. In this study, we evaluated the bioactivities of CPH on dextran sulfate solution (DSS)‐induced colitis in mice. The findings demonstrated that CPH supplementation improved body weight, food and water intake, and colon length. The therapeutic efficacy and immunoregulatory effect of CPH were further determined. Our results exhibited that CPH treatment significantly ameliorated pathological symptoms by enhancing intestinal integrity, mucin production, and goblet cell count. Moreover, the immunoregulatory effect of CPH on mRNA expression levels of different pro‐ and anti‐inflammatory cytokines was determined. Results exhibited a decrease in the expression of pro‐inflammatory cytokines and an increase in anti‐inflammatory cytokines in the colon. Additionally, the CPH administration modulates the nuclear factor kappa B (NF‐κB) pathway, preventing DNA damage and cell death. Assays for apoptosis and DNA damage revealed that CPH reduced oxidative DNA damage and apoptosis. These findings highlight the immunomodulatory and treatment amelioration effect of CPH in reducing the severity of colitis.

NF-κB pathway activation by Octopus peptide hydrolysate ameliorates gut dysbiosis and enhances immune response in cyclophosphamide-induced mice

Cyclophosphamide (CTX) is an anticancer medication that suppresses host immunity as well as adversely affects mucosal inflammation and gut microflora dysbiosis. The gut microflora is recognized as a substantial factor in host metabolism and immunological homeostasis. To improve immunity and inhibit cytotoxic and homeostatic imbalances triggered by CTX, it is essential to monitor immunoregulators. In this research, we assessed the impact of Octopus peptide hydrolysate (OPH) on immune modulation, intestinal integrity, and gut microbial composition in CTX-induced immune-deficient mice. The results revealed that OPH increased body weight, and immunological organ indices, and improved the histological changes in the colon, thymus, and spleen. The OPH stimulated the secretion of cytokines (IL-1β, IL-6, and TNF-α) and antibodies (IgM and IgA) while reducing the ratio of lipopolysaccharide (LPS) and diamine oxidase (DAO) in the serum. OPH further enhanced goblet cell and mucus production, upregulated the expression of gut tight-junction proteins (Occludin, Zonula Occludin-1, Mucin-2, and Claudin-1), and activated the TLR4/NF-κB cascade (p-IκBα, P65/p-p65). In addition, OPH treatment declined the Bacteroidetes/Firmicutes ratio, enhanced the relative ratio of Alistipes/Lachnospiraceae, and reversed the ecological equilibrium of the gut microflora. The findings revealed that OPH serves as a prebiotic to prevent CTX-mediated disruption in the intestinal barrier and boosts gut mucosal immunity by attenuating gut microflora imbalance, implying that OPH could be used as an immunological ingredient in nutritious foods to regulate the immune system and protect the gut from inflammatory diseases.

Enzymatic Preparation, Identification by Transmembrane Channel-like 4 (TMC4) Protein, and Bioinformatics Analysis of New Salty Peptides from Soybean Protein Isolate.

To address the public health challenges posed by high-salt diets, this study utilized pepsin and flavourzyme for the continuous enzymatic hydrolysis of a soy protein isolate (SPI). The separation, purification, and identification of salt-containing peptides in SPI hydrolysate were conducted using ultrafiltration (UF), gel filtration chromatography (GFC), and Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS). Subsequently, a molecular docking model was constructed between salt receptor protein transmembrane channel 4 (TMC4) and the identified peptides. Basic bioinformatics screening was performed to obtain non-toxic, non-allergenic, and stable salt peptides. After the enzymatic hydrolysis, separation, and purification of SPI, a component with a sensory evaluation score of 7 and an electronic tongue score of 10.36 was obtained. LC-MS/MS sequencing identified a total of 1697 peptides in the above component, including 84 potential salt-containing peptides. A molecular docking analysis identified seven peptides (FPPP, GGPW, IPHF, IPKF, IPRR, LPRR, and LPHF) with a strong theoretical salty taste. Furthermore, residues Glu531, Asp491, Val495, Ala401, and Phe405 of the peptides bound to the TMC4 receptor through hydrogen bonds, hydrophobic interactions, and electrostatic interactions, thereby imparting a significant salty taste. A basic bioinformatics analysis further revealed that IPHF, LPHF, GGPW, and IPKF were non-toxic, non-allergenic, and stable salt-containing peptides. This study not only provides a new sodium reduction strategy for the food industry, but also opens up new avenues for improving the public's healthy eating habits.

Bovine liver hydrolysates based on six proteases: Physicochemical properties, emulsification characteristics, antioxidant capacity assessment, and peptide identification

This study aimed to study the physicochemical, antioxidant, and emulsifying properties of bovine liver hydrolysates based on pepsin, alkaline protease, neutral protease, trypsin, papain, and flavor proteinase, and to identify proteins and peptides in bovine liver hydrolysates. The physicochemical properties of bovine liver hydrolysate were evaluated using gel permeation chromatography, surface hydrophobicity, fourier transforms infrared and fluorescence spectroscopy, and the antioxidant and emulsifying capacity of six bovine liver hydrolysates were characterized. The results showed that enzymatic hydrolysis by the six proteases decreased the molecular weight of the hydrolysate while increasing the content of hydrophobic amino acids and negatively charged amino acids. Among all proteases tested, alkaline protease exhibited the highest DH (13.3%) and protein recovery (37.3%). The concentration levels (1–5 mg/mL) positively correlated with antioxidant properties in alkaline protease hydrolysate, the hydrolysis ability of pepsin is relatively weak, and there is a significant difference between pepsin and other proteases, which was also reflected in its antioxidant capacity. Thus, alkaline protease hydrolysates were chosen for identification, and information on 3894 peptides was obtained, these findings provide a basis for expanding the application potential of bovine liver hydrolysate as a bioactive component in the food or pharmaceutical industry.

STUDY ON PREPARATION AND CHARACTERIZATION OF SACHI SEED OIL BASED EMULSION CONTAINING COLLAGEN PEPTIDES

In this study, collagen peptides were carried by a Sacha inchi (sachi) seed oil-based emulsion with Tween 80 under optimal conditions: 26.26% sachi seed oil, 26.06% Tween 80, and 47.68% distilled water. Collagen peptides, varying from 5 - 30% of the total emulsion mass, were dispersed in the aqueous phase before being introduced into the emulsion. Using the sachi seed oil-based emulsion to carry collagen peptides helps prevent the hydrolysis of collagen peptides by acids and enzymes in the digestive system. The characteristics of the emulsion were evaluated using dynamic light scattering, infrared spectroscopy, and ultraviolet-visible spectroscopy. The emulsions loaded with collagen peptides have average droplet sizes ranging from 83.57 - 286.93 nm. Emulsions carrying 5 - 10% collagen peptides exhibit a high stability for up to 30 days. These results demonstrate the potential application of sachi seed oil emulsions carrying collagen peptides in functional foods and healthcare products.

Chickpea (Cicer arietinum) protein hydrolysate ameliorates metabolic effects of feeding a high-fat diet to mice

The aim of this study was to identify peptides in chickpea protein hydrolysate (CPH) capable of ameliorating the metabolic consequences of a high-fat diet (HFD) using a model of metabolic dysfunction. C57BL/6J male mice were randomly divided into three groups (n = 13/group) and fed for 12 weeks a HFD + 0 mg CPH/kg body weight (BW) (0 CPH), HFD + 400 mg CPH/kg BW (400 CPH), or HFD + 800 mg CPH/kg BW (800 CPH). At the end, BW reduction in the 800 CPH group was 24.8 % compared to the control group (0 CPH) (p < 0.01). The 0 CPH group had the highest NAFLD score, and the 800 CPH group had the lowest. In liver, 400 CPH downregulated genes (fold change [FC] >1 or <−1) related to long-chain fatty acid uptake (Slc27a1), adipokine signaling (Tnfrsf1b) and insulin signaling (Pik3r1, Ikbkb, and Map2k1). CPH prevents NAFLD development by regulating inflammation and preventing steatosis via lipogenesis.

Structural and sensory characteristics of ultrasonic assisted wet-heating Maillard reaction products of Giant salamander protein hydrolysates.

Chinese giant salamander protein hydrolysates (CGSPH) are beneficial to human health as a result of their high content of amino acids and peptides. However, the formation of bitter peptides in protein hydrolysates (PHs) would hinder their application in food industry. The ultrasound assisted wet-heating Maillard reaction (MR) is an effective way to improve the flavor of PHs. Thus, the effect of ultrasonic assisted wet-heating MR on the structure and flavor of CGSPH was investigated in the present study. The results indicated that the ultrasound assisted wet-heating MR products (MRPs) exhibited a higher degree of graft and more significant changes in the secondary and tertiary structures of CGSPH compared to traditional wet-heating MRPs. Moreover, ultrasound assisted wet-heating MR could significantly increase the content of small molecule peptides and reduce the content of free amino acids of CGSPH, which resulted in more significant changes in flavor characteristics. The changed in flavor properties after MR (especially ultrasound assisted wet-heating MRPs) were mainly manifested by a significant reduction in bitterness, as well as a significant increase in the content of aromatic aldehyde ester compounds such as furan-2-carbaldehyde, butanal, benzaldehyde, furfural, etc. CONCLUSIONS: Ultrasound assisted wet-heating MR between CGSPH and xylose could be a promising way to improve the sensory characteristics of CGSPH. © 2024 Society of Chemical Industry.

Evaluating intestinal absorption of peptide Met-Lys-Pro in casein hydrolysate using Caco-2 and human iPS cell-derived small intestinal epithelial cells

High blood pressure is a major risk factor for cardiovascular disease. Our previous study confirmed that daily intake of casein hydrolysate that contained Met-Lys-Pro (MKP) can safely lower mildly elevated blood pressure. The present study aimed to evaluate the intestinal absorption differences between peptide MKP as a casein hydrolysate and synthetic MKP alone using Caco-2 cells and human iPS cell-derived small intestinal epithelial cells (hiSIECs). MKP was transported intact through Caco-2 cells and hiSIECs with permeability coefficient (Papp) values of 0.57 ± 0.14 × 10-7 and 1.03 ± 0.44 × 10-7 cm/s, respectively. This difference in Papp suggests differences in the tight junction strength and peptidase activity of each cell. Moreover, the transepithelial transport and residual ratio of intact MKP after adding casein hydrolysate containing MKP was significantly higher than that after adding synthetic MKP alone, suggesting that other peptides in casein hydrolysate suppressed MKP degradation and increased its transport. These findings suggest that hiSIECs could be useful for predicting the human intestinal absorption of bioactive peptides; ingesting MKP as a casein hydrolysate may also improve MKP bioavailability.

Assessment of the impact of whey protein hydrolysate on myofibrillar proteins in surimi during repeated freeze–thaw cycles: Quality enhancement and antifreeze potential

The quality of surimi, widely used in processed seafood, is compromised by freeze–thaw cycles, leading to protein denaturation and oxidative degradation. The objective of this study is to explore the effects of adding natural whey peptide hydrolysate (WPH) on the myofibrillar proteins of repeatedly freeze–thawed surimi. Results indicated surimi treated with 15% WPH exhibited only a 128% increase in surface hydrophobicity and a maximum peroxide value of 7.84 μg/kg, significantly lower than the control group. Additionally, salt-soluble protein content, emulsification activity, and stability decreased with the increase in freeze–thaw cycles. With a 15% WPH offering the most significant protective effect, evidenced by reductions of only 25.02%, 42.52% and 37.02% in salt-soluble protein content, emulsification activity, and stability, respectively. These outcomes demonstrate that WPH effectively reduces protein denaturation during repeated freeze–thaw processes. Future research should explore the molecular mechanisms underlying WPH's protective effects and evaluate their applicability in other food systems.

Release of CM-12 from A2-type casein by the cleavage of Ser-Leu-Xaa at the C-terminus using Aspergillus oryzae alkaline protease.

Aspergillus oryzae protease can release the opioid peptide β-casomorphin-10 (CM-10, YPFPGPIPNS, 60-69) from A2-type casein. However, not only is the yield of the active peptide low, but the key enzyme involved in processing has yet to be identified. A significant amount of the opioid peptide 60YPFPGPIPNSLP71 (CM-12) was produced from the A2-type casein peptide 53AQTQSLVYPFPGPIPNSLPQNIPPLTQTPV82 when the active protease in A. oryzae protease extract was fractionated with DEAE-Sepharose. The fractionated enzyme produced CM-12 from bovine A2-type casein but not from bovine A1 casein. A major protein of 34 kDa was purified and identified as an alkaline protease (Alp). Motif prediction of the Alp cleavage site using Multiple EM for Motif Elicitation analysis revealed preferable cleavage at the C-terminal end of Ser-Leu-Xaa for the release of CM-12. A2-type casein hydrolysate by Alp exhibited similar levels of opioid activity to that of synthetic CM-12 in cAMP-Glo assays with μ-opioid receptor-expressing HEK293 cells. These results suggest that CM-12 is a major opioid peptide in the casein hydrolysate. Our findings showed that Alp fractionated from A. oryzae protease extract produced the opioid peptide CM-12 from A2-type casein as a result of preferential cleavage at the C-terminal end of Ser-Leu-Xaa and the removal of coexisting enzymes. Moreover, docking predictions suggested a stable interaction between CM-12 and the 3D structure of Alp. Casein hydrolysate with Alp-containing CM-12 has the potential for use as a bioactive peptide material with opioid activity. © 2024 Society of Chemical Industry.

Identification and molecular mechanism of novel ACE inhibitory peptides from broccoli protein

Many natural angiotensin-converting enzyme inhibitory (ACEI) peptides have been widely studied and used to prevent and control hypertension. In this study, peptideomics and 3D-QSAR models combined with experimental verification were used to rapidly screen ACEI peptides in broccoli protein hydrolysates, followed by molecular docking and intracellular antihypertensive activity analysis. The results showed that two novel peptides FVLPLR and LPWYR were obtained, and their IC50 values for inhibiting ACE activity in vitro were 3.06 μM and 19.05 μM, respectively. Molecular docking results showed that FVLPLR and LPWYR bind to ACE through hydrogen bonding, electrostatic interaction, and hydrophobic interaction. Both peptides can promote HUVEC cells to produce vasodilator factor NO. These results indicated that broccoli protein could be used as an excellent source of ACE inhibitors.

Preparation, characterization and antioxidant activity analysis of three Maillard glycosylated bone collagen hydrolysates from chicken, porcine and bovine

Bone collagen hydrolysates (peptides) derived from byproduct of animal product processing have been used to produce commercially valuable products due to their potential antioxidant activity. Maillard glycosylated reaction is considered as a promising method to enhance the antioxidant activity of peptides. Hence, this research aims at investigating the Maillard glycosylation activity and antioxidant activity of bone collagen hydrolysates from different sources. In this study, 3 glycosylated bone collagen hydrolysates were prepared and characterized, and cytotoxicity and antioxidant activity were analyzed and evaluated. The free amino groups loss, browning intensity, and fluorescence intensity of G-Cbcp (glycosylated chicken bone collagen hydrolysates (peptides)) were the heaviest, followed by G-Pbcp (glycosylated porcine bone collagen hydrolysates (peptides)) and G-Bbcp (glycosylated bovine bone collagen hydrolysates (peptides)). The results of amino acid analysis showed that amino acid composition of different bone collagen hydrolysates was significantly different and the amino acid decreased to different degrees after Maillard glycosylated reaction, which may lead to differences in Maillard glycosylated reaction activity. Furthermore, the 3 glycosylated hydrolysates showed no significant cytotoxicity. The results showed that glycosylation process significantly increased the antioxidant activity of bone collagen hydrolysates, and G-Cbcp showed the strongest antioxidant activity, followed by G-Pbcp and G-Bbcp. Therefore, compared with the bone collagen hydrolysates, 3 glycosylated hydrolysates showed significant characteristic and structural changes, and higher antioxidant activity.

Hemoglobin Hydrolyzate Promotes Iron Absorption in the Small Intestine through Iron Binding Peptides.

Hemoglobin is an excellent source of iron supplements, and its hydrolyzate spontaneously binds iron during digestion and promotes iron absorption in vivo. However, the underlying mechanisms of what peptides bind and how they bind iron ions remain unclear. This study prepared the porcine hemoglobin hydrolyzate through enzymatic hydrolysis and acid treatment and investigated the mechanisms of hemoglobin hydrolyzate on iron absorption through the determination of iron levels in dietary intervention mice, iron binding site analyses, peptide digestion analyses, molecular simulation docking, and INT407 cell validation. The results showed that ingestion of the hemoglobin hydrolyzate diets increased iron levels in the blood of mice, accompanied by the upregulation of duodenal iron circulation-related genes such as ferritin, PCBP1, and HP. Carboxyl, imidazole groups, and aromatic amino acid residues were iron binding sites of hemoglobin hydrolyzate during digestion. VDEVGGEA and VDEVGGE were found to involve the spontaneous and efficient binding of hemoglobin hydrolyzate to iron ions in the intestinal cavity. In particular, the DEVGGE peptide was the typical sequence for hemoglobin hydrolytic peptides to exert iron binding activity.

Baltic herring hydrolysates: Identification of peptides, in silico DPP-4 prediction, and their effects on an in vivo mice model of obesity

Baltic herring is the main catch in the Baltic Sea; however, its usage could be improved due to the low processing rate. Previously we have shown that whole Baltic herring hydrolysates (BHH) and herring byproducts hydrolysates (BHBH) by commercial enzymes consisted of bioactive peptides and had moderate bioactivity in in vitro dipeptidyl peptidase (DPP)-4 assay. In this study, we identified the hydrolysate peptides by LC-MS/MS and predicted the potential bioactive DPP-4 inhibitory peptides using in silico tools. Based on abundance, peptide length and stability, 86 peptides from BHBH and 80 peptides from BHH were proposed to be novel DPP-4 inhibitory peptides. BHH was fed to a mice intervention of a high-fat, high-fructose diet to validate the bioactivity. The results of the glucose tolerance and insulin tolerance improved. Plasma DPP-4 activities, C-peptide levels, and HOMA-IR scores significantly decreased, while plasma glucagon-like peptide-1 content increased. In conclusion, BHH is an inexpensive and sustainable source of functional antidiabetic ingredients.