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.
Department of Microbiology, Albert Einstein College of Medicine, Bronx, New York 10461.
E J
EJ
Hehre
H
H
Matsui
C F
CF
Brewer
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