Both Acidic pH Value and Binding Interactions of Tartaric Acid With α-Glucosidase Cause the Enzyme Inhibition: The Mechanism in α-Glucosidase Inhibition of Four Caffeic and Tartaric Acid Derivates

Abstract

The inhibition mechanism of four caffeic and tartaric acid derivates, including caffeic acid (CA), tartaric acid (TA), caftaric acid (CFA) and chicoric acid (CHA) against α-glucosidase was characterized by substrate depletion, fluorescence quenching, isothermal titration calorimetry (ITC) and molecular docking. TA and CA were found with the highest and no inhibition effect respectively, and caffeoyl substitution at 2 and/or 3-OH of TA significantly decreased its inhibition. The enzyme inhibition effects of organic acids were not in an inhibitor concentration-dependent mode, and there was a rush increase in inhibition at a respective acidic pH value, especially for CFA and CHA, suggesting the important role of acidic pH in the enzyme inhibition for both compounds. Besides, CA, CFA and CHA were shown with strong quenching effects on α-glucosidase fluorescence because of π-conjugations between aromatic ring of caffeoyl moiety and that of enzyme fluorescent residues. However, no fluorescence quenching effect was observed for TA due to lack of aromatic ring. Additionally, a direct binding interaction behavior was observed for TA with α-glucosidase according to the fitted independent binding model in ITC, but not for CFA and CHA. Therefore, both acidic pH and binding interactions of TA with α-glucosidase resulted in the enzyme inhibition.

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

“…When there exist exogenous quenchers that have aromatic rings ( e.g ., benzene rings of polyphenols), non-covalent π-π conjugations (stackings) between the aromatic rings of polyphenols and that of the enzymes would form. The non-covalent interactions are able to “cover” the fluorescence property of the enzyme fluorophores ( 31 , 34 ). Thus, the fluorescence quenching effects of polyphenols can be observed.…”

“…In addition, the higher binding affinity of TA to AA corresponded to the higher inhibitory activity of TA against AA ( Table 1 ). On the other hand, the stoichiometry ( n ) that indicates the molar ratio of the ligand to the enzyme required to saturate the enzyme binding sites, as well as the entropy changes per molar titration (Δ S itc ) that indicates the degree of the order of the ligand-enzyme complex system, are two constants highly related with the number of binding sites and enzyme molecular conformation ( 34 , 37 ). Therefore, the difference in the structural properties of enzymes caused the difference in their values of n and Δ S itc for binding with TA ( Figure 4 ).…”

“…A TA® NanoITC isothermal titration calorimeter instrument was used to detect the enthalpy changes caused by the binding interactions between TA and the enzymes ( 17 , 34 ). Specifically, 50 μl of 5 mg/ml TA was loaded into an ITC syringe and was titrated into an ITC sample cell containing 170 μl of 1.5 mg/ml AA (or 7.5 mg/ml AMG) solution.…”

“…The thermal stability of enzymes in the absence and presence of TA was determined by use of a TA® Q2000 differential scanning calorimeter ( 17 , 34 ). Specifically, 50 μl of the respective enzyme solution (~50 mg/ml) was mixed with 50 μl of TA (60 mg/ml), followed by incubation at 4°C for 15 min.…”

Structural-Guided Identification of Small Molecule Inhibitor of UHRF1 Methyltransferase Activity

“…However, chicoric acid has been characterized as a more selective candidate with a higher LD50 value of 5000 mg/kg. Previously, chemoinformatics study of chicoric acid has been studied targeting various proteins ( Healy et al, 2009 ; Baskaran et al, 2012 ; Li et al, 2021 ). Till now no chemoinformatics study of chicoric acid-targeting SRA domain of UHRF1 has been elucidated.…”