Two potent competitive inhibitors discriminating α-glucosidase family I from family II Original Research Article

The inhibition kinetics for isoacarbose (a pseudotetrasaccharide, IsoAca) and acarviosine–glucose (pseudotrisaccharide, AcvGlc), both of which are derivatives of acarbose, were investigated with various types of α-glucosidases obtained from microorganisms, plants, and insects. IsoAca and AcvGlc, competitive inhibitors, allowed classification of α-glucosidases into two groups. Enzymes of the first group were strongly inhibited by AcvGlc and weakly by IsoAca, in which the Ki values of AcvGlc (0.35–3.0 μM) were 21- to 440-fold smaller than those of IsoAca. However, the second group of enzymes showed similar Ki values, ranging from 1.6 to 8.0 μM for both compounds. This classification for α-glucosidases is in total agreement with that based on the similarity of their amino acid sequences (family I and family II). This indicated that the α-glucosidase families I and II could be clearly distinguished based on their inhibition kinetic data for IsoAca and AcvGlc. The two groups of α-glucosidases seemed to recognize distinctively the extra reducing-terminal glucose unit in IsoAca.