Stereochemical studies of D-glucal hydration by alpha-glucosidases and exo-alpha-glucanases: indications of plastic and conserved phases in catalysis by glycosylases.

S. Chiba, C. F. Brewer, G. Okada, H. Matsui, E. J. Hehre

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Alpha-Glucosidases from Aspergillus niger, pig serum, ungerminated rice, buckwheat, and sugar beet seeds (but not from brewers' yeast or honeybee) were found to catalyze the hydration of D-glucal. Each reactive alpha-glucosidase, incubated with D-glucal in D2O, was shown to protonate (deuteriate) this prochiral substrate from above its re face, i.e., from a direction opposite that assumed for protonating alpha-D-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the alpha-glucosidases that acted rapidly enough in D2O to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (alpha-) configuration as the D-glucose produced from alpha-D-glucosidic substrates. These findings substantially extend those reported earlier for the hydration of D-glucal by one (Candida tropicalis) alpha-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by alpha-glucosidases (and perhaps glycosylases in general) may comprise two separate and separately controlled parts, namely, a "plastic" phase concerned with substrate protonation and a substrate-unrelated "conserved" phase concerned with the creation of product configuration. In contrast to the alpha-glucosidases, three "inverting" exo-alpha-glucanases (Arthrobacter globiformis glucodextranase; Rhizopus niveus and Paecilomyces varioti glucoamylase) were found to protonate D-glucal from below its si face. Further, whereas the catalysis of D-glucal hydration by the alpha-glucosidases was intensively inhibited by excess substrate, that promoted by the exo-glucanases showed no detectable substrate inhibition.

Original languageEnglish (US)
Pages (from-to)1464-1469
Number of pages6
JournalBiochemistry
Volume27
Issue number5
StatePublished - Mar 8 1988

ASJC Scopus subject areas

  • Biochemistry

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