Glycon specificity profiling of α-glucosidases using monodeoxy and mono-O-methyl derivatives of p-nitrophenyl α-d-glucopyranoside

Hydrolysis of probe substrates, eight possible monodeoxy and mono-O-methyl analogs of p-nitrophenyl α-d-glucopyranoside (pNP α-d-Glc), modified at the C-2, C-3, C-4, and C-6 positions, was studied as part of investigations into the glycon specificities of seven α-glucosidases (EC 3.2.1.20) isolated from Saccharomyces cerevisiae, Bacillus stearothermophilus, honeybee (two enzymes), sugar beet, flint corn, and Aspergillus niger. The glucosidases from sugar beet, flint corn, and A. niger were found to hydrolyze the 2-deoxy analogs with substantially higher activities than against pNP α-d-Glc. Moreover, the flint corn and A. niger enzymes showed hydrolyzing activities, although low, for the 3-deoxy analog. The other four α-glucosidases did not exhibit any activities for either the 2- or the 3-deoxy analogs. None of the seven enzymes exhibited any activities toward the 4-deoxy, 6-deoxy, or any of the methoxy analogs. The hydrolysis results, with the deoxy substrate analogs, demonstrated that α-glucosidases having remarkably different glycon specificities exist in nature. Further insight into the hydrolysis of deoxyglycosides was obtained by determining the kinetic parameters (kcat and Km) for the reactions of sugar beet, flint corn, and A. niger enzymes.