Question

Alpha-glycosidase catalyzes the hydrolysis of maltose into glucose.

a. Write the chemical reaction for the conversion of maltose into glucose (e.g. Reactants --> Products).
b. What type of chemical reaction is responsible for the conversion of maltose into glucose? Would you expect this reaction to occur quickly in the absence of alpha-glycosidase? Explain.
c. Draw a labeled diagram of an enzyme catalytic cycle that depicts the conversion of maltose into glucose. Be as detailed as you can.
d. Alpha-glycosidase is found in the saliva of most mammals. Suppose you were to ingest several saltine crackers (which are rich in starch) and then take a sip of lemonade (a solution which includes citric acid). How could the lemonade alter the efficacy of alpha-glycosidase?

Answer 1

As a key enzyme regulating postprandial blood glucose, α-Glucosidase is considered to be an effective target for the treatment of diabetes mellitus. In this study, a simple, rapid, and effective method for enzyme inhibitors screening assay was established based on α-glucosidase catalyzes reactions in a personal glucose meter (PGM). α-glucosidase catalyzes the hydrolysis of maltose to produce glucose, which triggers the reduction of ferricyanide (K3[Fe(CN)6]) to ferrocyanide (K4[Fe(CN)6]) and generates the PGM detectable signals. When the α-glucosidase inhibitor (such as acarbose) is added, the yield of glucose and the readout of PGM decreased accordingly. This method can achieve the direct determination of α-glucosidase activity by the PGM as simple as the blood glucose tests. Under the optimal experimental conditions, the developed method was applied to evaluate the inhibitory activity of thirty-four small-molecule compounds and eighteen medicinal plants extracts on α-glucosidase. The results exhibit that lithospermic acid (52.5 ± 3.0%) and protocatechualdehyde (36.8 ± 2.8%) have higher inhibitory activity than that of positive control acarbose (31.5 ± 2.5%) at the same final concentration of 5.0 mM. Besides, the lemon extract has a good inhibitory effect on α-glucosidase with a percentage of inhibition of 43.3 ± 3.5%. Finally, the binding sites and modes of four active small-molecule compounds to α-glucosidase were investigated by molecular docking analysis. These results indicate that the PGM method is feasible to screening inhibitors from natural products with simple and rapid operations.

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