Inhibition by nojirimycin and 1-deoxynojirimycin of microsomal glucosidases from calf liver acting on the glycoprotein oligosaccharides Glc_1–3Man₉GlcNAc₂

Abstract

Particulate membrane fractions from calf liver catalyze the release of glucose from GlcNAc₂-Man₉-Glc_1–3-oligosaccharides. Maximal oligosaccharide-glucosidase activity was obtained at pH 6.2 and a detergent concentration of 0.5% Triton X-100. This activity could be distinguished from non-specific α-glucosidase activity on the basis of different pH-dependence and lack of activation by detergent. The relative rates for the hydrolysis of the Glc₃-, Glc₂- , and Glc_l-oligosaccharide , estimated from the initial velocity, was 1∶12∶3. There is no significant difference in the enzyme activity towards free, peptide-bound, or lipid-linked oligosaccharide.

Nojirimycin and l-deoxynojirimycin were strong inhibitors of microsomal oligosaccharide-glucosidases. Hydrolysis of GIc₃-oligosaccharide was inhibited by 50% at concentrations of 0.16 mM and 2 μM, respectively. Hydrolysis of the Glc₂- and Glc₁-oligosaccharide was inhibited to a somewhat lower extent, suggesting the presence of at least two glucosidases, one acting on Glc₃- and one acting on Glc₁- and Glc₂-oligosaccharide.