Hydrolysis of α- and β-d-glucosyl fluoride by individual glucosidases: new evidence for separately controlled "plastic" and "conserved" phases in glycosylase catalysis

Hirokazu Matsui, Yoshimasa Tanaka, Curtis F. Brewer, John S. Blanchard, Edward J. Hehre

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α-Glucosidases from sugar beet seed and ungerminated rice catalyzed the hydrolysis of β-d-glucopyranosyl fluoride to form α-d-glucose. The reactions were slow, with V/K = 11-15 × 10-3 or ∼ 1-2% of that for hydrolysis of p-nitrophenyl α-d-glucopyranoside, but were not due to any impurity in the substrate or to contaminating β-glucosidase or glucoamylase. Furthermore, almond β-glucosidase promoted hydrolysis of α-d-glucosyl fluoride to form β-d-glucose at an exceedingly low rate, V/K = 4 × 10-4. This weak reaction did not stem from any impurity in the substrate or to contamination with α-glucosidase or glucoamylase, but it was partly (∼ 20%) attributable to a trace of accompanying trehalase. That all three glucosidases acted upon both α- and β-d-glucosyl fluoride, albeit at low efficiency with the disfavored anomer, reflects the previously demonstrated ability of each enzyme's catalytic groups to respond flexibly to substrates of different types. That the disfavored d-glucosyl fluoride in each case was converted into a product of the same configuration as from enitols or favored d-glucosyl substrates provides additional evidence for the two-step nature of the chemical mechanisms of glucosidases, in which the stereochemistry of water attack on the enzyme-stabilized oxocarbonium ion is strictly maintained, regardless of the initial anomeric configuration of the substrate.

Original languageEnglish (US)
Pages (from-to)45-56
Number of pages12
JournalCarbohydrate Research
Issue number1
Publication statusPublished - Dec 16 1993


ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Organic Chemistry

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