Hydrolysis of beta-D-glucopyranosyl fluoride to alpha-D-glucose catalyzed by Aspergillus niger alpha-D-glucosidase.
Aspergillus niger alpha-D-glucosidase, crystallized and free of detectable activity for beta-D-glucosides, catalyzes the slow hydrolysis of beta-D-glucopyranosyl fluoride to form alpha-D-glucose. Maximal initial rates, V, for the hydrolysis of beta-D-glucosyl fluoride, p-nitrophenyl alpha-D-glucopyranoside, and alpha-D-glucopyranosyl fluoride are 0.27, 0.75, and 78.5 mumol.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 beta-D-glucosyl fluoride and not from a contaminating trace of alpha-D-glucosyl fluoride, and is catalyzed by the alpha-D-glucosidase and not by an accompanying trace of beta-D-glucosidase or glucoamylase. Maltotriose competitively inhibits the hydrolysis, and beta-D-glucosyl fluoride in turn competitively inhibits the hydrolysis of p-nitrophenyl alpha-D-glucopyranoside, indicating that beta-D-glucosyl fluoride is bound at the same site as known substrates for the alpha-glucosidase. Present findings provide new evidence that alpha-glucosidases are not restricted to alpha-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.
Hehre
E J
EJ
Department of Microbiology, Albert Einstein College of Medicine, Bronx, New York 10461.
Matsui
H
H
Brewer
C F
CF
D001234:Aspergillus niger / Q000201:enzymology*; D002384:Catalysis; D005947:Glucose / Q000031:analogs & derivatives* / Q000378:metabolism*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D013237:Stereoisomerism; D000520:alpha-Glucosidases / Q000378:metabolism*
C030364:glucosyl fluoride; D000520:alpha-Glucosidases; D005947:Glucose