Stereochemical studies of D-glucal hydration by α-glucosidases and exo-α-glucanases: indications of plastic and conserved phases in catalysis by glycosylasest

Seiya Chiba, Curtis F. Brewer, Gentaro Okada, Hirokazu Matsui, Edward J. Hehre

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

α-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 α-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 α-D-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the α-glucosidases that acted rapidly enough in D2O to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (a-) configuration as the D-glucose produced from α-D-glucosidic substrates. These findings substantially extend those reported earlier for the hydration of D-glucal by one (Candida tropicalis) α-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by α-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 α-glucosidases, three "inverting" exo-α-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 α-glucosidases was intensively inhibited by excess substrate, that promoted by the exo-glucanases showed no detectable substrate inhibition.

Original languageEnglish (US)
Pages (from-to)1564-1569
Number of pages6
JournalBiochemistry
Volume27
Issue number5
StatePublished - 1988

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Calcium Gluconate
Glucosidases
Catalysis
Hydration
Plastics
Substrates
exo-1,6-alpha-glucosidase
Paecilomyces
Fagopyrum
Sugar beets
Candida tropicalis
Arthrobacter
Glucan 1,4-alpha-Glucosidase
Rhizopus
Beta vulgaris
Aspergillus niger
Candida
Aspergillus
Protonation
Deoxyglucose

ASJC Scopus subject areas

  • Biochemistry

Cite this

Stereochemical studies of D-glucal hydration by α-glucosidases and exo-α-glucanases : indications of plastic and conserved phases in catalysis by glycosylasest. / Chiba, Seiya; Brewer, Curtis F.; Okada, Gentaro; Matsui, Hirokazu; Hehre, Edward J.

In: Biochemistry, Vol. 27, No. 5, 1988, p. 1564-1569.

Research output: Contribution to journalArticle

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N2 - α-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 α-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 α-D-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the α-glucosidases that acted rapidly enough in D2O to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (a-) configuration as the D-glucose produced from α-D-glucosidic substrates. These findings substantially extend those reported earlier for the hydration of D-glucal by one (Candida tropicalis) α-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by α-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 α-glucosidases, three "inverting" exo-α-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 α-glucosidases was intensively inhibited by excess substrate, that promoted by the exo-glucanases showed no detectable substrate inhibition.

AB - α-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 α-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 α-D-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the α-glucosidases that acted rapidly enough in D2O to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (a-) configuration as the D-glucose produced from α-D-glucosidic substrates. These findings substantially extend those reported earlier for the hydration of D-glucal by one (Candida tropicalis) α-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by α-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 α-glucosidases, three "inverting" exo-α-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 α-glucosidases was intensively inhibited by excess substrate, that promoted by the exo-glucanases showed no detectable substrate inhibition.

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