HYDROLYSIS OF β-D-GLUCOPYRANOSYL FLUORIDE TO α-D-GLUCOSE CATALYZED BY Aspergillus niger α-D-GLUCOSIDASE

Article abstract of DOI:10.1016/0008-6215(90)84282-Y

Aspergillus niger α-D-glucosidase, crystallized and free of detectable activity for β-D-glucosides, catalyzes the slow hydrolysis of β-D-glucopyranosyl fluoride to form α-D-glucose.Maximal initial rates, V, for the hydrolysis of β-D-glucosylfluoride, p-nitrophenyl α-D-glucopyranoside, and α-D-glucopyranosyl fluoride are 0.27, 0.75, and 78.5 μmol*min^-1*mg^-1, respectively, with corresponding V/K constants of 0.0068, 1.44, and 41.3.Independent lines of evidence make clear that the reaction stems from β-D-glucosyl fluoride and not from a contaminating trace of α-D-glucosyl fluoride, and is catalyzed by the α-D-glucosidase and not by an accompanying trace of β-D-glucosidase or glucoamylase.Maltotriose competitively inhibits the hydrolysis, and β-D-glucosyl fluoride in turn competetively inhibits the hydrolysis of p-nitrophenyl α-D-glucopyranoside, indicating that β-D-glucosylfluoride is bound at the same site as known substrates for the α-glucosidase.Present findings provide new evidence that α-glucosidases are not restricted to α-D-glucosylic substrates or to reactions providing retention of configuration.They strongly support the concept that product configuration in glycosylase-catalyzed reactions is primarily determined by enzyme structures controlling the direction of approach of acceptor molecules to the reaction center rather than by the anomeric configuration of the substrate.