The inhibitory effects of free and bound phenolics from Phyllanthus emblica Linn. on α-amylase: a comparison study

BACKGROUND

Phyllanthus emblica Linn. (PE) is rich in polyphenols, which can be categorized into free and bound phenolics (PEFP and PEBP). This study evaluated the inhibitory effect of PEFB and PEBP on α-amylase for the first time. The mechanism of the inhibition effect of PEFP and PEBP on α-amylase was investigated by enzyme inhibition kinetics, multispectral analysis, thermodynamics, and molecular docking.

RESULTS

Free and bound phenolics inhibited α-amylase activity effectively in a mixed type of inhibition. Fluorescence quenching and thermodynamic analyses showed that the binding of PEFP and PEBP to α-amylase occurred through a static quenching process (Kq = 6.94 × 10¹² and 5.74 × 10¹² L mol-1 s-1), which was accompanied by a redshift (λem from 343 to 347 nm), leading to a change in the microenvironment. This process was found to be a spontaneous exothermic reaction (ΔG < 0). Circular dichroism (CD) analysis confirms that the secondary structure of α-amylase was altered, in particular a decrease in α-helixes and an increase in random coils. Molecular docking studies showed that PEFP and PEBP interacted with α-amylase through hydrogen bonding and hydrophobic interactions.

CONCLUSION

The present study provides valuable insights into the mechanism of action of PEFP and PEBP on α-amylase, which will provide a theoretical basis for their possible use as novel natural α-amylase inhibitors. © 2024 Society of Chemical Industry.

The inhibition mechanism of bound polyphenols extracted from mung bean coat dietary fiber on porcine pancreatic α-amylase: kinetic, spectroscopic, differential scanning calorimetric and molecular docking

The inhibitory mechanisms of purified bound polyphenols extracted from mung bean coat dietary fiber (pMBDF-BP) on porcine pancreatic α-amylase (PPA) were investigated through inhibition kinetics, fluorescence spectroscopy, circular dichroism, differential scanning calorimetry and molecular docking. It was shown that pMBDF-BP exerted significant reversible inhibition on PPA in a mixed-type inhibition manner (IC50 = 18.57 ± 0.30 μg/mL), and the combination of the three major components exhibited a synergistic inhibitory effect on PPA. Further, pMBDF-BP bound to the active site or form a polyphenol-enzyme complex at the inactive site through hydrogen bonding and hydrophobic forces, via enhancing the hydrophobicity of the microenvironment surrounding tryptophan and tyrosine residues and promoting the secondary structure of PPA towards a more stable conformation, eventually reducing the enzyme activity. This study provided theoretical evidences for the utilization of bound polyphenols extracted from mung bean coat dietary fiber as a functional component in natural inhibitors of α-amylase.

The substitution sites of hydroxyl and galloyl groups determine the inhibitory activity of human pancreatic α-amylase in twelve tea polyphenol monomers

Tea polyphenols have been reported as potential α-amylase inhibitors. However, the quantitative structure-activity relationship (QSAR) between tea polyphenols and human pancreas α-amylase (HPA) is not well understood. Herein, the inhibitory effect of twelve tea polyphenol monomers on HPA was investigated in terms of inhibitory activity, as well as QSAR analysis and interaction mechanism. The results revealed that the HPA inhibitory activity of theaflavins (TFs), especially theaflavin-3'-gallate (TF-3'-G, IC50: 0.313 mg/mL), was much stronger than that of catechins (IC50: 18.387-458.932 mg/mL). The QSAR analysis demonstrated that the determinant for the inhibitory activity of HPA was not the number of hydroxyl and galloyl groups in tea polyphenol monomers, while the substitution sites of these groups potentially might play a more important role in modulating the inhibitory activity. The inhibition kinetics and molecular docking revealed that TF-3'-G as a mixed-type inhibitor had the lowest inhibition constant and bound to the active sites of HPA with the lowest binding energy (-7.74 kcal/mol). These findings could provide valuable insights into the structures-activity relationships between tea polyphenols and the HPA inhibitors.

The Antiobesity Effects and Potential Mechanisms of Theaflavins

Theaflavins are the characteristic polyphenols in black tea which can be enzymatically synthesized. In this review, the effects and molecular mechanisms of theaflavins on obesity and its comorbidities, including dyslipidemia, insulin resistance, hepatic steatosis, and atherosclerosis, were summarized. Theaflavins ameliorate obesity potentially via reducing food intake, inhibiting pancreatic lipase to reduce lipid absorption, activating the adenosine monophosphate-activated protein kinase (AMPK), and regulating the gut microbiota. As to the comorbidities, theaflavins ameliorate hypercholesterolemia by inhibiting micelle formation to reduce cholesterol absorption. Theaflavins improve insulin sensitivity by increasing the signaling of protein kinase B, eliminating glucose toxicity, and inhibiting inflammation. Theaflavins ameliorate hepatic steatosis via activating AMPK. Theaflavins reduce atherosclerosis by upregulating nuclear factor erythropoietin-2-related factor 2 signaling and inhibiting plasminogen activator inhibitor 1. In randomized controlled trails, black tea extracts containing theaflavins reduced body weight in overweight people and improved glucose tolerance in healthy adults. The amelioration on the hyperlipidemia and the prevention of coronary artery disease by black tea extracts were supported by meta-analysis.

Lowering glycemic levels via gastrointestinal tract factors: the roles of dietary fiber, polyphenols, and their combination

Dietary fiber (DF) and polyphenols (DP) are typical blood sugar-lowering components, and both play distinct yet interconnected roles in exerting their blood sugar-lowering effects. We comprehensively summarized the single and combined effects of DF and DP on blood glucose homeostasis through regulating the relevant factors in the upper gastrointestinal tract (UGT) and lower gastrointestinal tract (LGT). In the UGT, DF slowed down glucose metabolism by enhancing digesta viscosity and hindering enzyme-substrate interaction. DP primarily targeted enzymes and substrates. When combined, DP enhanced the adsorption capacity of DF for glucose. DF weakened DP's inhibitory effect on enzymes. Both DF and DP disrupted glucose intestinal uptake via physical or genomic modulation, but the co-consumption of DF and DP demonstrated a lower inhibitory effect on glucose uptake than DP alone. In the LGT, DF and DP showed synergistic or antagonistic effects on gut microbiota. Remarkably, whole foods exhibited potent prebiotic effects due to their compound-rich matrix, potentially enhancing glucose homeostasis and expanding dietary options for glucose regulation research.

Inhibitory activities and rules of plant gallotannins with different numbers of galloyl moieties on sucrase, maltase and α-amylase in vitro and in vivo

BACKGROUND

α-Glucosidase inhibitors could effectively reduce postprandial blood glucose (PBG) levels and control the occurrence of complications of diabetes. Gallotannins (GTs) in plants have attracted much attention due to their significant α-glucosidase inhibitory activities in vitro. However, there is still a lack of systematic comparative studies to further elucidate inhibitory activities in vivo and in vitro of these compounds against α-glucosidase, especially for mammalian sucrase and maltase, and analyze their structure-activity relationship.

PURPOSE

Determine the in vitro and in vivo inhibitory activities of five GTs with different number of galloyl moieties (GMs) on sucrase, maltase and α-amylase, and elucidate the relationship between α-glucosidase inhibitory activities and the number and connection mode of GMs.

METHODS

Molecular docking and dynamics were used to study the binding mode and binding ability of five GTs against sucrase, maltase and α-amylase. Then, the inhibitory activities and inhibitory mechanisms of these compounds on sucrase, maltase and α-amylase in vitro were studied using inhibitory assay and enzyme inhibition kinetics. Further, the hypoglycemic effects in vivo of these compounds were demonstrated by three polysaccharides tolerance experiments on diabetes model mice.

RESULTS

The results of molecular docking showed that these compounds could bind to enzymes through hydrogen bonds, hydrophobic interactions, etc. In addition, the α-glucosidase inhibition comparative studies in vitro and in vivo demonstrated that the inhibitory activities of these compounds on all three sucrase, maltase and α-amylase were ranked as TA ≈ PGG > TeGG > TGG > 1GG, and their inhibitory activities increases with the increase in the number of GMs. Moreover, the hypoglycemic effects of 1,2,3,4,6-pentagalloylglucose (PGG) and tannic acid (TA) in vitro and in vivo were also confirmed to be equivalent to or even stronger than that of acarbose.

CONCLUSION

α-Glucosidase inhibitory activities in vitro and in vivo of GTs were positively correlated with the number of GTs, and the more the number, the stronger the activity. However, PGG with five GTs and TA with ten GTs showed almost identical α-glucosidase inhibitory activities, possibly due to the reduced binding force with the enzyme caused by spatial hindrance.

Gallate Moiety of Catechin Is Essential for Inhibiting CCL2 Chemokine-Mediated Monocyte Recruitment

Leukocyte recruitment witnesses an orchestrated complex formation between the chemokines and their molecular partners. CCL2 chemokine that regulates monocyte trafficking is a worthwhile system from the pharmaceutical perspective. In the current study, four major catechins (EC/EGC/ECG/EGCG) were assessed for their inhibitory potential against CCL2-regulated monocyte/macrophage recruitment. Interestingly, catechins with the gallate moiety (ECG/EGCG) could only attenuate the CCL2-induced macrophage migration. These molecules specifically bound to CCL2 on a pocket comprising the N-terminal, β₀-sheets, and β₃-sheets, and the binding affinity of ECGC (K_d = 22 ± 4 μM) is ∼4 times higher than that of the ECG complex (K_d = 85 ± 6 μM). MD simulation analysis evidenced that the molecular specificity/stability of CCL2-catechin complexes is regulated by multiple factors, including stereospecificity, number of hydroxyl groups on the annular ring-B, the positioning of the carbonyl group, and the methylation of the galloyl ring. Further, a significant overlap on the binding surface of CCL2 for EGCG/ECG and receptor interactions as evidenced from NMR data provided the rationale for the observed inhibition of macrophage migration in response to EGCG/ECG binding. In summary, these galloylated epicatechins can be considered as potent protein-protein interaction (PPI) inhibitors that regulate CCL2-directed leukocyte recruitment for resolving inflammatory/immunomodulatory disorders.

Action mechanisms of two key xanthine oxidase inhibitors in tea polyphenols and their combined effect with allopurinol

BACKGROUND

Tea polyphenols have been reported to have the effect of lowering uric acid. However, there are few studies on the inhibitory effects and molecular mechanisms of specific catechins on the urate-metabolizing enzyme xanthine oxidase (XO). In this research, multiple spectroscopic methods and computer simulations were used to determine the inhibitory ability and mechanisms of epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG) on XO.

RESULTS

Herein, EGCG and GCG reversibly inhibited XO activity in a mixed manner, with IC₅₀ values of 40.50 ± 0.32 and 33.60 ± 0.53 μmol L^-1 , and also decreased the superoxide anion radical (O₂ ^- ) of the catalytic system by reducing the XO molecule and inhibiting the formation of uric acid. The combination of EGCG or GCG with allopurinol showed synergistic inhibition on XO. The binding of EGCG or GCG to XO with moderate affinity formed a stable complex by hydrogen bonds and van der Waals forces. The presence of EGCG and GCG made the structure of XO more stable and compact. The two inhibitors bound to the vicinity of flavin adenine dinucleotide (FAD) in XO, hindering the entry of substrate; thus the activity of XO was suppressed.

CONCLUSION

Both EGCG and GCG are excellent natural XO inhibitors, and inhibited the activity of XO by occupying the channel of the substrate to enter the active center and interfering with the dual substrate reaction catalyzed by XO. These findings provide a scientific basis for the application of catechins in dietary supplements and medicines with lowering uric acid effects. © 2022 Society of Chemical Industry.

Hypoglycemic and antioxidative activity evaluation of phenolic compounds derived from walnut diaphragm produced in Xinjiang

Walnut diaphragm is defined as a dry wood septum located between the walnut shell and kernel. In this work, seven phenolic compounds from walnut diaphragm were purified and characterized, and their antioxidant activities and mechanisms of hypoglycemia were investigated. Compounds 1-7 were tested for DPPH, ABTS scavenging ability, and FRAP assay to evaluate the antioxidant activity. α-Amylase inhibition assay was introduced to assess the hypoglycemic activity, and the mechanism was investigated by kinetic analysis, CD spectrum, and molecular docking. Compound 6 showed the strongest antioxidant ability, while compound 1 exhibited the strongest inhibition of α-amylase by changing the secondary structure of α-amylase in a mixed competitive inhibition mode. Molecular docking test predicted that the tetrahydropyran part in compound 1 may contribute to its hypoglycemic effect. This study furnishes a new theoretical reference for the utilization and development of walnut diaphragm into a health food with antioxidant and hypoglycemic properties. PRACTICAL APPLICATIONS: The finding of this research may serve as a basis for the subsequent development of walnut diaphragm into instant tea-based health food or added to other food carriers to achieve auxiliary antioxidant and hypoglycemic effects. This study revealed that polyphenolic components were the material basis for the antioxidant and hypoglycemic effects of walnut diaphragm, which could be identified as landmark chemical components for controlling quality standards in the development of walnut diaphragm, thus accelerating the research process of quality standards for walnut diaphragm-related products. Furthermore, the studies on the mechanism of hypoglycemic activity supply more credible data to support the development of walnut diaphragm into a safe and consumer-friendly health food. With abundant resources and clear efficacy, walnut diaphragm has great development prospect and application value.

Enzymic catalyzing affinity to substrate affects inhibitor-enzyme binding interactions: Inhibition behaviors of EGCG against starch digestion by individual and co-existing α-amylase and amyloglucosidase

The inhibition of (-)-epigallocatechin-gallate (EGCG) against starch digestion by α-amylase (AA), amyloglucosidase (AMG) and co-existing enzymes (AA/AMG) were comparatively studied. EGCG inhibited AA only at slowly-digestible-starch (SDS) phase. This resulted from high catalytic efficiency of AA for rapidly-digestible-starch (RDS), counteracting the inhibition at this phase. EGCG inhibited AMG and AA/AMG during whole process. At RDS phase, the catalytic velocity of AMG was always higher than AA/AMG because of an antagonistic effect of two enzymes. However, at SDS phase with EGCG, the catalytic velocity of AA/AMG was higher than AMG. This is because binding of EGCG with both enzymes caused more unbound AMG that generated more glucose in co-existing AA/AMG than AMG. Although EGCG-AA binding affinity was higher than EGCG-AMG, competitive inhibition of EGCG against AA was weaker than AMG, indicating relatively higher binding/catalyzing affinity of AA to starch significantly weakened EGCG-AA binding due to competitive relationship between starch and EGCG.

α-Amylase Changed the Catalytic Behaviors of Amyloglucosidase Regarding Starch Digestion Both in the Absence and Presence of Tannic Acid

The courses of starch digestion with individual α-amylase (AA), amyloglucosidase (AMG), and AA/AMG bi-enzyme system were performed and analyzed by first-order-reaction equations in the absence and presence of tannic acid (TA). An antagonistic effect between AA and AMG occurred at the digestion phase of readily-digestible starch due to the higher catalytic efficiency of AMG for starchy-substrates with more complex structures. This effect caused a faster rate of glucose production with AMG than with AA/AMG bi-enzyme system at this phase both in the absence and presence of TA. TA had a higher binding affinity to AA than to AMG as accessed by several methods, such as inhibition kinetics, fluorescence quenching, isothermal titration calorimetry (ITC), and molecular docking. Besides, differential scanning calorimetry (DSC) indicated that the change in the thermal and structural stabilities of enzymes in the presence of TA was related to the enzyme residues involved in binding with TA, rather than the inhibitory effects of TA. The binding characters of TA to both enzymes resulted in more “free” AMG without TA binding in AA/AMG bi-enzyme system than that in individual AMG. This binding property caused more and faster rate of glucose production at the digestion phase of slowly digestible starch (SDS) in the bi-enzyme system.

The Phenolics and Antioxidant Properties of Black and Purple versus White Eggplant Cultivars

The total phenolic content, anthocyanins, phenolic acids, antioxidant capacity and α-amylase inhibitory activity of black (Aydin Siyahi), purple (Kadife Kemer) and white (Trabzon Kadife) eggplants grown in Turkey were subjected to a comparative investigation. The black cultivar exhibited the highest total phenolic (17,193 and 6552 mg gallic acid equivalent/kg fw), flavonoid (3019 and 1160 quercetin equivalent/kg fw) and anthocyanin (1686 and 6167 g delphinidin-3-O-glucoside equivalent/kg fw) contents in crude extracts of the peel and pulp. The majority of the caffeic acid was identified in the ester (2830 mg/kg fw) and ester-bound (2594 mg/kg fw) forms in the peel of ‘Kadife Kemer’ and in the glycoside form (611.9 mg/kg fw) in ‘Aydin Siyahi’, as well as in the pulp of these two eggplants. ‘Kadife Kemer’ (purple eggplant) contained the majority of the chlorogenic acid in free form (27.55 mg/kg fw), compared to ‘Aydin Siyahi’ in the ester (7.82 mg/kg fw), glycoside (294.1 mg/kg dw) and ester-bound (2.41 mg/kg fw) forms. The eggplant cultivars (peel and pulp, mg/kg fw) exhibited a relatively high delphinidin-3-O-rutinoside concentration in the peel of ‘Aydin Siyahi’ (avg. 1162), followed by ‘Kadife Kemer’ (avg. 336.6), and ‘Trabzon Kadife’ (avg. 215.1). The crude phenolic extracts of the eggplants exhibited the highest antioxidant capacity values (peel and pulp, µmoL Trolox equivalent/kg fw) of 2,2-diphenyl-1-picrylhydrazyl (DPPH, 8156 and 2335) and oxygen radical absorbance capacity (ORAC, 37,887 and 17,648). The overall results indicate that black and purple eggplants are the cultivars with greater potential benefits in terms of their phenolics and antioxidant values than the white eggplant.

Caffeoyl substitution decreased the binding and inhibitory activity of quinic acid against α-amylase: The reason why chlorogenic acid is a relatively weak enzyme inhibitor

α-Amylase inhibition of chlorogenic acid (CHA) and its component moieties including quinic acid (QA) and caffeic acid (CA) were characterized by IC₅₀, inhibition kinetics, fluorescence quenching, isothermal titration calorimetry, differential scanning calorimetry and molecular docking. QA was found with the highest inhibitory activity in a competitive-mode, and caffeoyl substitution significantly decreased its inhibition but maintained inhibition type. Interestingly, QA hardly quenched α-amylase fluorescence, while CA quenched that significantly without inhibitory activity. This resulted from lack of aromatic ring in QA that can form π-conjugation with α-amylase fluorescent residues. Besides, the binding constant of QA with α-amylase was higher than CHA. Additionally, QA and CA decreased but CHA remained α-amylase thermal stability, indicating that change in α-amylase spatial structure was related with enzyme residue sites involved in interactions with inhibitors, instead of with inhibition effect. Conclusively, caffeoyl substitution decreased α-amylase inhibition of QA through reducing its binding affinity to the enzyme.

Essential moieties of myricetins, quercetins and catechins for binding and inhibitory activity against α-Glucosidase

α-Glucosidase inhibition of 11 flavonoids, including myricetins, quercetins and catechins were studied through initial reaction velocity, IC₅₀ value, inhibition kinetics, fluorescence quenching and molecular docking. It was found that C4 = O, C2 = C3, 3-OH and 5'-OH were essential moieties for α-glucosidase inhibition of myricetin that was shown with the highest inhibitory activity. The trans-conformational catechins was shown with stronger inhibition effects than the cis-conformational ones. Further, gallocatechin was an uncompetitive inhibitor, while myricetin, myricetrin, quercetin and catechin were competitive ones. 3-OH and 5'-OH promoted myricetin to bind with the enzyme active site through hydrogen bondings. The presence of C4 = O and C2 = C3 increased electron delocalization in ring A-C for myricetin and quercetin, and this enhanced stability of π-conjugations with aromatic residues of amino acids. However, 5'-OH decreased the quenching effects because it limited π-conjugations of ring B with key fluorescent residues. Notably, for same flavonoid sort, the constants that indicate binding affinity of flavonoids to α-glucosidase, including reciprocal of competitive inhibition constant, fluorescence quenching constant and binding energy followed same order as the inhibitory activity, indicating that α-glucosidase inhibition of the flavonoids resulted from binding interactions between them, and that the methods above can be combined reasonably to characterize flavonoid-enzyme binding interactions.

The Physical Adsorption of Gelatinized Starch with Tannic Acid Decreases the Inhibitory Activity of the Polyphenol against α-Amylase

The effects of mixing orders of tannic acid (TA), starch, and α-amylase on the enzyme inhibition of TA were studied, including mixing TA with α-amylase before starch addition (order 1), mixing TA with pre-gelatinized starch before α-amylase addition (order 2) and co-gelatinizing TA with starch before α-amylase addition (order 3). It was found that the enzyme inhibition was always highest for order 1 because TA could bind with the enzyme active site thoroughly before digestion occurred. Both order 2 and 3 reduced α-amylase inhibition through decreasing binding of TA with the enzyme, which resulted from the non-covalent physical adsorption of TA with gelatinized starch. Interestingly, at low TA concentration, α-amylase inhibition for order 2 was higher than order 3, while at high TA concentration, the inhibition was shown with the opposite trend, which arose from the difference in the adsorption property between the pre-gelatinized and co-gelatinized starch at the corresponding TA concentrations. Moreover, both the crystalline structures and apparent morphology of starch were not significantly altered by TA addition for order 2 and 3. Conclusively, although a polyphenol has an acceptable inhibitory activity in vitro, the actual effect may not reach the expected one when taking processing procedures into account.

Number of galloyl moiety and intramolecular bonds in galloyl-based polyphenols affect their interaction with alpha-glucosidase

The inhibition of α-glucosidase by nine galloyl-based polyphenols with free and unfree galloyl moieties (GMs) was studied. The results show that the inhibitory activity increased with the free GM number increasing. For the compounds with unfree GMs, ellagic acid and hexahydroxydiphenoyl group contributed to the enzyme inhibition. Free GMs could bind not only with the active site of α-glucosidase (competitive inhibition character), but also with the non-active sites (uncompetitive one); however, the former binding interaction was stronger than the latter one. All polyphenols that had inhibitory effects quenched α-glucosidase fluorescence in a static mode through forming a polyphenol-enzyme complex. The number of amino acid residues involved in polyphenol-enzyme binding interactions (hydrogen bonding and π-conjugations) increased with the inhibitory activity increasing. Additionally, two polyphenols with 5 free GMs showing certain hypoglycemic effects in maltose-loading test suggests that GM may be an advisable functional factor for alleviation of type II diabetes symptoms.

The galloyl moiety enhances the inhibitory activity of catechins and theaflavins against α-glucosidase by increasing the polyphenol-enzyme binding interactions

The inhibition properties of 10 tea polyphenols against α-glucosidase were studied through inhibition assay, inhibition kinetics, fluorescence quenching and molecular docking. It was found that the inhibitory activity of polyphenols with a 3 and/or 3' galloyl moiety (GM) was much higher than that without a GM. The GM could enter into the active site of α-glucosidase and bind with the catalytic amino acid residues through hydrogen bonding and π-conjugation, thus playing an important role in the competitive inhibition of catechins and theaflavins. The positive linear correlations among the constants characterizing the inhibitory activity and binding affinity of tea polyphenols to α-glucosidase indicate that enzyme inhibition by polyphenols is caused by the binding interactions between them, and that the combination of the characterization methods for polyphenol-glucosidase binding is reasonable. In addition, the in vivo hypoglycemic effects of galloylated polyphenols suggest that the GM may be considered as a pharmaceutical fragment for the alleviation of type II diabetes symptoms through α-glucosidase inhibition.

Insight into interaction mechanism between theaflavin-3-gallate and α-glucosidase using spectroscopy and molecular docking analysis

To elucidate the α-glucosidase (α-GC) inhibitory mechanism of theaflavin-3-gallate (TF-3-G), their interaction mechanism was investigated using spectroscopy and molecular docking analysis. The inhibition ratio of TF-3-G against α-GC was determined to be 92.3%. Steady fluorescence spectroscopy showed that TF-3-G effectively quenched the intrinsic fluorescence of α-GC through static quenching, forming a stable complex through hydrophobic interactions. Formation of the TF-3-G/α-GC complex was also confirmed by resonance light scattering spectroscopy. Synchronous fluorescence spectroscopy and circular dichroism spectroscopy indicated that the secondary structure of α-GC was changed by TF-3-G. Molecular docking was used to simulate TF-3-G/α-GC complex formation, showing that TF-3-G might be inserted into the hydrophobic region around the active site of ɑ-GC, and bind with the catalytic Asp215 and Asp352 residues. The ɑ-GC inhibitory mechanism of TF-3-G was mainly attributed to the change in ɑ-GC secondary structure caused by the complex formation. PRACTICAL APPLICATIONS: α-Glucosidase (α-GC) can hydrolyze the glycosidic bonds of starch and oligosaccharides in food and release glucose. Therefore, the inhibition of α-GC activity has been used to treat postprandial hyperglycemia and type 2 diabetes mellitus. Theaflavin-3-gallate (TF-3-G), a flavonoid found in the fermentation products of black tea, exhibits strong inhibition of α-GC activity. However, the α-GC inhibitory mechanism of TF-3-G is unclear. This study aids understanding of this mechanism, and proposed a possibly basic theory for improving the medicinal value of TF-3-G in diabetes therapy.