Optimization and Molecular Mechanism of Novel α-Glucosidase Inhibitory Peptides Derived from Camellia Seed Cake through Enzymatic Hydrolysis

A new technique for antioxidant walnut peptide preparation directly from walnut cake: Enzymatic preparation process optimization coupled with enzyme membrane reactor and kinetic analysis

The lack of scalable production methods limits the commercial production viability of walnut peptides. To overcome this obstacle, enzyme membrane reactors (EMRs) were used to continuously produce bioactive peptides (called CEMR) directly from walnut cake. The optimum operating conditions were pH 10.7, an [E/S] ratio of 11 %, and a temperature of 44 °C, which resulted in a peptide yield of 256.0 ± 4.66 mg/g cake and a protein conversion degree reaching 63.49 ± 0.82 %. Kinetic analysis showed that affinity between alkaline protease and walnut cake can be enhanced by EMR (km decreased, kA increased). The antioxidant results showed that the strongest antioxidant activity was detected in CEMR. The composition of amino acids and molecular weight distribution results showed that the highest content of Glu (20.20 ± 0.48 %), Asp (20.70 ± 0.95 %), and peptides with molecular weight < 1KD (51.92 %) were detected in CEMR. The results of CEMR provide a new option for simplifying the production process of walnut peptide.

α-Glucosidase inhibitory peptides from the enzymolysis of Semen Ziziphi Spinosae protein using an ultrasound-assisted protease: Preparation and inhibitory mechanism

Peptides are promising sources of safe hypoglycemic drugs. The potential of Semen Ziziphi Spinosae protein (SZSP) as a natural source of α-glucosidase inhibitory peptides was investigated. SZSP was hydrolyzed using an ultrasound-assisted protease, and the four α-glucosidase inhibitory peptides were purified, identified, and screened. Their inhibitory mechanisms were investigated using molecular docking. Ultrasound-assisted enzymolysis enhanced the α-glucosidase inhibition and protein conversion rates, which cleaved the protein into small molecules. Fourier transform infrared spectroscopy results showed that the protease hydrolysis tended to transform α-helicals into β-sheets. A purification, identification, and screening process finally identified four α-glucosidase inhibitory peptides. The IC50 values of LPLLDK, PRLPEM, LPWK, and FPPR were 120.36 ± 6.73, 139.50 ± 7.21, 248.12 ± 10.27, and 106.67 ± 3.22 μM, respectively. Lineweaver-Burk analyses demonstrated that FPPR was a competitive inhibitor of -glucosidase, while LPLLDK and LPWK exhibited a mixed inhibition mechanism and PRLPEM was a non-competitive inhibitor. Molecular docking studies indicated that polypeptides occupy the active pockets of -glucosidase through hydrogen bonding, hydrophobic interactions, and salt Bridges, preventing -glucosidase from forming complexes with the substrate or non-competitive binding to other sites to form enzyme-substrate inhibitors to inhibit enzyme-substrate intermediates and prevent the release of catalytic reaction products. These results demonstrate that the peptides extracted from SZSP may be beneficial for the treatment of diabetes.

Computational screening for novel α-glucosidase inhibitory peptides from Chlamys nobilis adductor muscle as a potential antidiabetic agent

Introduction

This study aimed to evaluate the adjuvant hypoglycemic function of enzyme hydrolyzate (EHCA) from Chlamys nobilis in mice and to identify α-glucosidase inhibitory peptides.

Methods

The α-glucosidase inhibitory and radical scavenging ability of EHCA were determined in vitro, and the effects on blood glucose regulation and the antioxidant activity were evaluated in vivo using a mouse model. Peptides with potential α-glucosidase inhibitory activity were identified by LC-MS/MS and confirmed in silico.

Results and Discussion

EHCA exhibited significant α-glucosidase inhibitory activity and radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH). in vivo, EHCA significantly improved the glucose tolerance of mice, reduced malondialdehyde and increased the superoxide dismutase activity in liver. Five novel peptides were identified, with Lys-Leu-Asn-Ser-Thr-Thr-Glu-Lys-Leu-Glu-Glu and Thr-Asp-Ala-Asp-His-Lys-Phe showing strong inhibitory effects on α-glucosidase (IC50 value of 144.89 μM and 136.96 μM, respectively). The interactions between peptides and α-glucosidase were driven by hydrogen bonds, van der Waals forces, and hydrophobic interactions. These findings suggest that EHCA and its derived peptides could serve as potential adjuvant agents for blood glucose regulation and antioxidant activity. The identified peptides may pave the way for the development of alternative α-glucosidase inhibitors.

The Effects of Sika Deer Antler Peptides on 3T3-L1 Preadipocytes and C57BL/6 Mice via Activating AMPK Signaling and Gut Microbiota

(1) Background: To explore the anti-obesity effects and mechanisms of sika deer velvet antler peptides (sVAP) on 3T3-L1 preadipocytes and in high-fat diet (HFD)-induced obese mice. (2) Methods: sVAP fractions of different molecular weights were obtained via enzymatic hydrolysis and ultrafiltration. Their anti-lipid effects on 3T3-L1 cells were assessed with Oil Red O staining. The optimal fraction was tested in HFD-induced obese C57BL/6 mice to explore anti-obesity mechanisms. Peptide purification used LC-MS/MS, followed by sequence analysis and molecular docking for activity prediction. (3) Results: The peptide with the best anti-obesity activity was identified as sVAP-3K (≤3 kDa). sVAP-3K reduced lipid content and proliferation in 3T3-L1 cells, improved lipid profiles and ameliorated adipocyte degeneration in HFD mice, promoted the growth of beneficial gut microbiota, and maintained lipid metabolism. Additionally, sVAP-3K activated the AMP-activated protein kinase (AMPK) signaling pathway, regulating adipogenic transcription factors. sVAP-3K exhibited ten major components (peak area ≥ 1.03 × 108), with four of the most active components being newly discovered natural oligopeptides: RVDPVNFKL (m/z 363.21371), GGEFTPVLQ (m/z 474.24643), VDPENFRL (m/z 495.25735), and VDPVNFK (m/z 818.44043). (4) Conclusion: This study identifies four novel oligopeptides in sVAP-3K as key components for anti-obesity effects, offering new evidence for developing natural weight-loss drugs from sika deer velvet.

Identification and Molecular Mechanism of Novel α-Glucosidase Inhibitory Peptides from the Hydrolysate of Hemp Seed Proteins: Peptidomic Analysis, Molecular Docking, and Dynamics Simulation

There is a growing demand for natural and potent α-glucosidase inhibitors due to the rising prevalence of diabetes. In this study, newly identified α-glucosidase inhibitory peptides were identified from the tryptic hydrolysate of hemp seed proteins based on peptidomics and in silico analysis. A total of 424 peptides, primarily derived from four cupin-type-1 domain-containing proteins, were identified, and 13 ultimately were selected for validation based on their higher PeptideRanker scores, solubility, non-toxicity, and favorable ADMET properties. Molecular docking revealed that these 13 peptides primarily interacted with α-glucosidase via hydrogen bonding and hydrophobic interactions. Among them, three novel peptides-NPVSLPGR (-8.7 kcal/mol), LSAERGFLY (-8.5 kcal/mol), and PDDVLANAF (-8.4 kcal/mol)-demonstrated potent α-glucosidase inhibitory activity due to their lower binding energies than acarbose (-8.1 kcal/mol), the first approved α-glucosidase inhibitor for type 2 diabetes treatment. The molecular mechanism analysis revealed that the peptides NPVSLPGR and LSAERGFLY inhibited α-glucosidase by simultaneously blocking substrate entry through occupying the entrance of the active site gorge and preventing catalysis by binding to active sites. In contrast, the peptide PDDVLANAF primarily exerted inhibitory effects by occupying the entrance of the active site gorge. Molecular dynamics simulation validated the stability of the complexes and provided additional insights into the molecular mechanism determined through docking. These findings contribute essential knowledge for the advancement of natural α-glucosidase inhibitors and offer a promising approach to effectively manage diabetes.

Inhibition of α-glucosidase activity by potential peptides derived from fermented spent coffee grounds

The control of α-glucosidase activity has been associated with managing diabetes. We previously identified three peptides with high bioactive indices derived from protein hydrolysates of fermented spent coffee grounds. In this study, the peptides YGF, GMCC, and RMYRY were synthesized and tested in vitro for their α-glucosidase inhibition activity, complemented by in silico analyses. Two of the three peptides significantly inhibited α-glucosidase activity, with the more efficient peptides being YGF and GMCC (0.42 mg/mL), resulting in decreased enzymatic activity of 95.31% and 89.79%, respectively. These peptides exhibited binding free energies with the α-glucosidase complex of -8.5 and - 6.6 kcal/mol, respectively, through hydrogen bonds and van der Waals interactions with amino acids from the active site. Pharmacokinetic analysis indicated that YGF and GMCC profiles were unrelated to toxicity. These results underscore the importance of focusing on food waste bioprocessing products to expand the range of alternatives that could aid in diabetes treatment.

Plant-Derived as Alternatives to Animal-Derived Bioactive Peptides: A Review of the Preparation, Bioactivities, Structure-Activity Relationships, and Applications in Chronic Diseases

Background/Objectives: At present, a large number of bioactive peptides have been found from plant sources with potential applications for the prevention of chronic diseases. By promoting plant-derived bioactive peptides (PDBPs), we can reduce dependence on animals, reduce greenhouse gas emissions, and protect the ecological environment. Methods: In this review, we summarize recent advances in sustainably sourced PDBPs in terms of preparation methods, biological activity, structure-activity relationships, and their use in chronic diseases. Results: Firstly, the current preparation methods of PDBPs were summarized, and the advantages and disadvantages of enzymatic method and microbial fermentation method were introduced. Secondly, the biological activities of PDBPs that have been explored are summarized, including antioxidant, antibacterial, anticancer and antihypertensive activities. Finally, based on the biological activity, the structure-activity relationship of PDBPs and its application in chronic diseases were discussed. All these provide the foundation for the development of PDBPs. However, the study of PDBPs still has some limitations. Conclusions: Overall, PDBPs is a good candidate for the prevention and treatment of chronic diseases in humans. This work provides important information for exploring the source of PDBPs, optimizing its biological activity, and accurately designing functional foods or drugs.

Efficient recovery of functional biomolecules from shrimp (Litopenaeus vannamei) processing waste for food and health applications via a successive co-culture fermentation approach

This study developed a food-grade fermentation process that efficiently isolated proteins and minerals from shrimp-processing waste (SPW). The in vitro antioxidant and enzyme inhibitory effects of SPW hydrolysates obtained from the fermentation process were investigated. SPW broths were prepared from the head (SPW-SH) and body carapace (SPW-SS) of Pacific white shrimp (Litopenaeus vannamei) and fermented using a 5-day successive co-culture fermentation approach with Bacillus amyloliquefaciens TISTR-1880 and Lactobacillus casei TBRC-388. This bacterial combination demonstrated optimal efficiency in extracting proteins (up to 93% deproteinization) and minerals (up to 83% demineralization) from SPW samples compared with other studied co-culture combinations. The resulting SPW-SH and SPW-SS hydrolysates were rich in proteins (∼70 and ∼59 g/100 g dry weight, respectively). They exhibited significantly enhanced antioxidant potential compared to their corresponding non-fermented controls at up to 2.3 and 3.7-fold higher, respectively as determined by the ORAC, FRAP, and DPPH radical scavenging assays. The two SPW hydrolysates also had significantly higher inhibitory activities against angiotensin-converting enzyme, α-amylase, and lipase than the controls, indicating their improved anti-hypertension, anti-diabetes, and anti-obesity properties, respectively; however, both SPW-SH and SPW-SS hydrolysates did not inhibit α-glucosidase at the tested concentrations. The SPW hydrolysates produced in this study showed high potential for use as functional ingredients in food and nutraceutical products. Knowledge gained from this study can promote the prospective valorization of industrial SPW as an inexpensive source of functional biomolecules for food-related applications using a fermentation approach. This will increase the commercial value of SPW and reduce the environmental impact.

In vitro and in silico assessment of antidiabetic and antioxidant potencies of secondary metabolites from Gymnema sylvestre

This study investigated the chemical constituents, antioxidant potential, and in vitro and in silico antidiabetic activity of Gymnema sylvestre. Column chromatography and spectroscopic techniques identified twelve compounds from the methanol extract, including 4 sterols (1-4), 5 triterpenoids (5-9), and 3 flavonoids (10-12). The chemophenetic significance of all compounds was also investigated. The antioxidant capacity of the extract and compounds (1-4) was evaluated using FRAP and DPPH assays. The extract exhibited strong free radical scavenging activity (IC50 = 48.34 µg/mL), while compounds (1-4) displayed varying degrees of efficacy (IC50 = 98.30-286.13 µg/mL). The FRAP assay indicated significant reducing power for both extract and compounds (58.54, 47.61, 56.61, and 49.11 mg Eq.VitC/g for extract and compounds 1 & 2, 3, and 4, respectively). The antidiabetic potential was assessed through α-amylase and α-glucosidase enzyme inhibition assays. The crude extract demonstrated the most potent inhibition (IC50 = 218.46 and 57.42 µg/mL for α-glucosidase and α-amylase respectively) suggesting its potential for managing postprandial hyperglycaemia. In silico studies employed molecular docking and dynamics simulations to elucidate the interactions between identified compounds and α-amylase/α-glucosidase enzymes. The results revealed promising binding affinities between the compounds and target enzymes, with compound 6 demonstrating the highest predicted inhibitory activity with -10 kcal/mol and -9.1 kcal/mol for α-amylase and α-glucosidase, respectively. This study highlights the presence of diverse bioactive compounds in Gymnema sylvestre. The extract exhibits antioxidant properties and inhibits carbohydrate-digesting enzymes, suggesting its potential as a complementary therapeutic approach for managing hyperglycaemia associated with type 2 diabetes.

Extraction, identification, and molecular mechanisms of α-glucosidase inhibitory peptides from defatted Antarctic krill (Euphausia superba) powder hydrolysates

The objective of this study was to explore the potential of Antarctic krill-derived peptides as α-glucosidase inhibitors for the treatment of type 2 diabetes. The enzymolysis conditions of α-glucosidase inhibitory peptides were optimized by response surface methodology (RSM), a statistical method that efficiently determines optimal conditions with a limited number of experiments. Gel chromatography and LC-MS/MS techniques were utilized to determine the molecular weight (Mw) distribution and sequences of the hydrolysates. The identification and analysis of the mechanism behind α-glucosidase inhibitory peptides were conducted through conventional and computer-assisted techniques. The binding affinities between peptides and α-glucosidase were further validated using BLI (biolayer interferometry) assay. The results revealed that hydrolysates generated by neutrase exhibited the highest α-glucosidase inhibition rate. Optimal conditions for hydrolysis were determined to be an enzyme concentration of 6 × 103 U/g, hydrolysis time of 5.4 h, and hydrolysis temperature of 45 °C. Four peptides (LPFQR, PSFD, PSFDF, VPFPR) with strong binding affinities to the active site of α-glucosidase, primarily through hydrogen bonding and hydrophobic interactions. This study highlights the prospective utility of Antarctic krill-derived peptides in curtailing α-glucosidase activity, offering a theoretical foundation for the development of novel α-glucosidase inhibitors and related functional foods to enhance diabetes management.

Anti-diabetic properties of brewer's spent yeast peptides. In vitro, in silico and ex vivo study after simulated gastrointestinal digestion

Brewer's spent yeast (BSY) hydrolysates are a source of antidiabetic peptides. Nevertheless, the impact of in vitro gastrointestinal digestion of BSY derived peptides on diabetes has not been assessed. In this study, two BSY hydrolysates were obtained (H1 and H2) using β-glucanase and alkaline protease, with either 1 h or 2 h hydrolysis time for H1 and H2, respectively. These hydrolysates were then subjected to simulated gastrointestinal digestion (SGID), obtaining dialysates D1 and D2, respectively. BSY hydrolysates inhibited the activity of α-glucosidase and dipeptidyl peptidase IV (DPP-IV) enzymes. Moreover, although D2 was inactive against these enzymes, D1 IC50 value was lower than those found for the hydrolysates. Interestingly, after electrophoretic separation, D1 mannose-linked peptides showed the highest α-glucosidase inhibitory activity, while non-glycosylated peptides had the highest DPP-IV inhibitory activity. Kinetic analyses showed a non-competitive mechanism in both cases. After peptide identification, GILFVGSGVSGGEEGAR and IINEPTAAAIAYGLDK showed the highest in silico anti-diabetic activities among mannose-linked and non-glycosylated peptides, respectively (AntiDMPpred score: 0.70 and 0.77). Molecular docking also indicated that these peptides act as non-competitive inhibitors. Finally, an ex vivo model of mouse jejunum organoids was used to study the effect of D1 on the expression of intestinal epithelial genes related to diabetes. The reduction of the expression of genes that codify lactase, sucrase-isomaltase and glucose transporter 2 was observed, as well as an increase in the expression of Gip (glucose-dependent insulinotropic peptide) and Glp1 (glucagon-like peptide 1). This is the first report to evaluate the anti-diabetic effect of BSY peptides in mouse jejunum organoids.

Virtual Screening Technology for Two Novel Peptides in Soybean as Inhibitors of α-Amylase and α-Glucosidase

Soybean peptides (SPs) have bioactivities of enzyme inhibition that are beneficial to human health, but their mechanism is not clear. This study aimed to identify peptide fragments in SPs that simultaneously inhibit α-amylase and α-glucosidase and to explore their enzyme inhibition mechanism. Firstly, the inhibitory activity of SPs against the enzymes was determined. And two octapeptides, LDQTPRVF and SRNPIYSN, were identified for the first time by using HPLC-QTOF-MS/MS and virtual screening. Molecular simulation results showed that hydrogen bonds and π-π bonds were the key factors, and the N-terminal (Leu and Ser) and C-terminal (Phe) of peptide were important inhibiting sites. Both octapeptides were synthesized, and their IC50 values were 3.08 and 5.58 mmol/L for α-amylase, and 2.52 and 4.57 mmol/L for α-glucosidase, respectively. This study provided evidence for SPs as a potential inhibitor of α-amylase and α-glucosidase in special dietary foods.

Emerging therapeutic options in the management of diabetes: recent trends, challenges and future directions

Diabetes is a serious health issue that causes a progressive dysregulation of carbohydrate metabolism due to insufficient insulin hormone, leading to consistently high blood glucose levels. According to the epidemiological data, the prevalence of diabetes has been increasing globally, affecting millions of individuals. It is a long-term condition that increases the risk of various diseases caused by damage to small and large blood vessels. There are two main subtypes of diabetes: type 1 and type 2, with type 2 being the most prevalent. Genetic and molecular studies have identified several genetic variants and metabolic pathways that contribute to the development and progression of diabetes. Current treatments include gene therapy, stem cell therapy, statin therapy, and other drugs. Moreover, recent advancements in therapeutics have also focused on developing novel drugs targeting these pathways, including incretin mimetics, SGLT2 inhibitors, and GLP-1 receptor agonists, which have shown promising results in improving glycemic control and reducing the risk of complications. However, these treatments are often expensive, inaccessible to patients in underdeveloped countries, and can have severe side effects. Peptides, such as glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), are being explored as a potential therapy for diabetes. These peptides are postprandial glucose-dependent pancreatic beta-cell insulin secretagogues and have received much attention as a possible treatment option. Despite these advances, diabetes remains a major health challenge, and further research is needed to develop effective treatments and prevent its complications. This review covers various aspects of diabetes, including epidemiology, genetic and molecular basis, and recent advancements in therapeutics including herbal and synthetic peptides.

Screening and Activity Analysis of α-Glucosidase Inhibitory Peptides Derived from Coix Seed Prolamins Using Bioinformatics and Molecular Docking

Hydrolysates of coix seed prolamins (CHPs) have an excellent hypoglycemic effect and can effectively inhibit α-glucosidase, which is the therapeutic target enzyme for type 2 diabetes mellitus. However, its hypoglycemic components and molecular mechanisms remain unclear, and its stability in food processing needs to be explored. In this study, four potential α-glucosidase inhibitory peptides (LFPSNPLA, FPCNPLV, HLPFNPQ, LLPFYPN) were identified and screened from CHPs using LC-MS/MS and virtual screening techniques. The results of molecular docking showed that the four peptides mainly inhibited α-glucosidase activity through hydrogen bonding and hydrophobic interactions, with Pro and Leu in the peptides playing important roles. In addition, CHPs can maintain good activity under high temperatures (40~100 °C) and weakly acidic or weakly alkaline conditions (pH 6.0~8.0). The addition of glucose (at 100 °C) and NaCl increased the inhibitory activity of α-glucosidase in CHPs. The addition of metal ions significantly decreased the inhibitory activity of α-glucosidase by CHPs, and their effects varied in magnitude with Cu2+ having the largest effect followed by Zn2+, Fe3+, K+, Mg2+, and Ca2+. These results further highlight the potential of CHPs as a foodborne hypoglycemic ingredient, providing a theoretical basis for the application of CHPs in the healthy food industry.

Development and Identification of Novel α-Glucosidase Inhibitory Peptides from Mulberry Leaves

The mulberry leaf is a botanical resource that possesses a substantial quantity of protein. In this study, alcalase hydrolysis conditions of mulberry leaf protein were optimized using the response surface method. The results showed that the optimum conditions were as follows: substrate protein concentration was 0.5% (w/v), enzymatic hydrolysis temperature was 53.0 °C, enzymatic hydrolysis time was 4.7 h, enzyme amount was 17,800 U/g, and pH was 10.5. Then mulberry leaf peptides were separated by ultrafiltration according to molecular weight. Peptides (<3 kDa) were screened and subsequently identified using LC-MS/MS after the evaluation of α-glucosidase inhibition across various fractions. Three novel potential bioactive peptides RWPFFAFM (1101.32 Da), AAGRLPGY (803.91 Da), and VVRDFHNA (957.04 Da) with the lowest average docking energy were screened for molecular dynamics simulation to examine their binding stability with enzymes in a 37 °C simulated human environment. Finally, they were prepared by solid phase synthesis for in vitro verification. The former two peptides exhibited better IC50 values (1.299 mM and 1.319 mM, respectively). These results suggest that the α-glucosidase inhibitory peptides from mulberry leaf protein are potential functional foods or drugs for diabetes treatment, but further in vivo studies are needed to identify the bioavailability and toxicity.

Optimization of a Novel Tyrosinase Inhibitory Peptide from Atrina pectinata Mantle and Its Molecular Inhibitory Mechanism

In order to realize the multi-level utilization of marine shellfish resources and to develop the potential biological activity of processing by-products of Atrina pectinata, gelatin was extracted from the mantle and the potential whitening effect of its enzymatic peptides was explored. Taking tyrosinase inhibitory activity as the evaluation index, the enzyme hydrolysate process was optimized by response-surface methodology, and the optimal enzyme hydrolysate conditions were as follows: pH 5.82, 238 min enzyme hydrolysate time, and temperature of 54.5 °C. Under these conditions, the tyrosinase inhibition activity of Atrina pectinata mantle gelatin peptide (APGP) was 88.6% (IC50 of 3.268 ± 0.048 mg/mL). The peptides obtained from the identification were separated by ultrafiltration and LC-MS/MS, and then four new peptides were screened by molecular docking, among which the peptide Tyr-Tyr-Pro (YYP) had the strongest inhibitory effect on tyrosinase with an IC50 value of 1.764 ± 0.025 mM. The molecular-docking results indicated that hydrogen bonding is the main driving force for the interaction of the peptide YYP with tyrosinase. From the Lineweaver-Burk analysis, it could be concluded that YYP is inhibitory to tyrosinase and exhibits a mixed mechanism of inhibition. These results suggest that YYP could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals.

Alpha-Glucosidase Inhibitory Peptides: Sources, Preparations, Identifications, and Action Mechanisms

With the change in people's lifestyle, diabetes has emerged as a chronic disease that poses a serious threat to human health, alongside tumor, cardiovascular, and cerebrovascular diseases. α-glucosidase inhibitors, which are oral drugs, have proven effective in preventing and managing this disease. Studies have suggested that bioactive peptides could serve as a potential source of α-glucosidase inhibitors. These peptides possess certain hypoglycemic activity and can effectively regulate postprandial blood glucose levels by inhibiting α-glucosidase activity, thus intervening and regulating diabetes. This paper provides a systematic summary of the sources, isolation, purification, bioavailability, and possible mechanisms of α-glucosidase inhibitory peptides. The sources of the α-glucosidase inhibitory peptides were introduced with emphasis on animals, plants, and microorganisms. This paper also points out the problems in the research process of α-glucosidase inhibitory peptide, with a view to providing certain theoretical support for the further study of this peptide.