Amperometric measurement of α-glucosidase activity using hydroquinone-α-D-glucopyranoside as a substrate

A convenient electrochemical method for the assay of a-glucosidase was developed using hydroquinone-alpha-D-glucopyranoside (alpha-arbutin) as a substrate. The concentration of p-hydroquinone produced by the hydrolysis of alpha-arbutin was measured by amperometry with a membrane-covered glassy carbon electrode at 0.4 V. By the addition of alpha-glucosidase to a buffer solution containing alpha-arbutin, the current began to increase linearly. The initial rate of hydrolysis was calculated from the slope of the current-time curve. The initial rate was increased with increasing the concentration of alpha-arbutin, and tended to approach the saturation value, whereas it was proportional to the concentration of alpha-glucosidase. The Michaelis constant (K-m) for alpha-arbutin by alpha-glucosidase was 0.45 mM. There was the good correlation between the enzymatic activity of alpha-glucosidase determined by the present method and that determined by a spectrophotometric method using p-nitrophenyi-D-glucopyranoside as a substrate. Compared with the spectrophotometric method, the electrochemical method has advantages of being free from the influence of turbidity and coloration of a sample solution. Therefore, the activity of alpha-glucosidase in a solution extracted from rice koji could be measured without any filtration treatment.