Acarbose and 1-Deoxynojirimycin Inhibit Maltose and Maltooligosaccharide Hydrolysis of Human Small Intestinal Glucoamylase–Maltase in Two Different Substrate-Induced Modes

The inhibition of the glucoamylase–maltase-catalyzed maltose and maltooligosaccharide hydrolysis by acarbose and 1-deoxynojirimycin has been demonstrated. Acarbose and 1-deoxynojirimycin act as potent competitive inhibitors withKi= 0.8 μmfor the hydrolysis of maltose and withKivalues of 0.4 and 0.3 μm, respectively, for the hydrolysis of maltooligosaccharides. In a previous work (Güntheret al., Arch. Biochem. Biophys.327, 295–302, 1996) using maltitol and maltobionate as inhibitors we were able to discriminate two different binding modes for glucoamylase–maltase: a maltose and an oligosaccharide binding mode. Here we found that structurally quite different substances, namely, the pseudotetrasaccharide acarbose and the monomeric glucose analog 1-deoxynojirimycin, act as competitive inhibitors for maltose and maltooligosaccharide hydrolysis. TheKivalues for all used maltooligosaccharides are nearly equal, but for maltose hydrolysis theKivalues are significantly higher by a magnitude factor of two. The differences concerningKivalues can be explained by means of the two-binding-mode model.