Alpha-secondary tritium kinetic isotope effects for the hydrolysis of alpha-D-glucopyranosyl fluoride by exo-alpha-glucanases.

H. Matsui, J. S. Blanchard, C. F. Brewer, E. J. Hehre

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

alpha-Secondary tritium kinetic isotope effects ranging from 1.17 to 1.26 were measured for the hydrolysis of alpha-D-glucopyranosyl fluoride (forming beta-D-glucose) catalyzed by several glucoamylases and a glucodextranase. These results indicate that cleavage of the C-F bond is slow and that the enzymic transition state has significant oxo-carbonium ion character. Strong support for this conclusion is provided by the agreement found in the case of Rhizopus niveus glucoamylase (alpha-TV/K 1.26; Km 26 mM) between measured values of the alpha-secondary deuterium kinetic isotope effects (alpha-DV/K 1.16; alpha-DV 1.20) and those calculated from the tritium isotope effect. The data are consistent with the promotion of an intramolecular elimination of fluoride by the present exo-alpha-glucanases based on their ability to stabilize, perhaps with a counter ion, the development of a carbonium ion-like transition state. Although the oxo-carbonium ion is formally denoted as an intermediate it could represent a transition state along a reaction pathway to a covalent glucosyl intermediate.

Original languageEnglish (US)
Pages (from-to)8714-8716
Number of pages3
JournalThe Journal of biological chemistry
Volume264
Issue number15
StatePublished - May 25 1989

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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