Scope and mechanism of carbohydrase action. Stereocomplementary hydrolytic and glucosyl-transferring actions of glucoamylase and glucodextranase with alpha- and beta-D-glucosyl fluoride

• Published in: The Journal of biological chemistry 1981-06, Vol.256 (12), p.6017-6026
• Main Authors: Kitahata, S, Brewer, C F, Genghof, D S, Sawai, T, Hehre, E J
• Format: Article
• Language: English
• Subjects: Arthrobacter - enzymology; Arthrobacter globiformis; exo-1,4- alpha -D-glucosidase; exo-1,6- alpha -D-glucosidase; Glucan 1,4-alpha-Glucosidase - metabolism; Glucans - metabolism; Glucose - analogs & derivatives; Glucose - metabolism; Glucose - pharmacology; Glucosidases - metabolism; Glycosides - metabolism; Hydrofluoric Acid; Kinetics; mechanisms; Methylglucosides - metabolism; Methylglucosides - pharmacology; Rhizopus - enzymology; Rhizopus niveus; Stereoisomerism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)69122-2

Rhizopus niveus glucoamylase and Arthrobacter globiformis glucodextranase, which catalyze the hydrolysis of starch and dextrans, respectively, to form D-glucose of inverted (beta) configuration, were found to convert both alpha- and beta-D-glucosyl fluoride to beta-D-glucose and hydrogen fluoride. Each enzyme directly hydrolyzes alpha-D-glucosyl fluoride but utilizes th beta-anomer in reactions that require 2 molecules of substrate and yield glucosyl transfer products which are then rapidly hydrolyzed to form beta-D-glucose. Various D-glucopyranosyl compounds serve as acceptors for such reactions. Mixtures of beta-D-glucosyl fluoride and methyl-alpha-D-glucopyranoside[14C], incubated with either enzyme, yielded both methyl-alpha-D-glucopyranosyl-(1 leads to 4)-alpha-D-[14C]glucopyranoside and methyl-alpha-D-glucopyranosyl-(1 leads to 6)-alpha-D-[14C]glucopyranoside. Glucoamylase produced more of the alpha-maltoside; glucodextranase produced more of the alpha-isomaltoside. Thus, both "exo-alpha-glucan hydrolases" emerge as glucosylases that catalyze stereospecifically complementary hydrolytic and transglucosylative reactions with glucosyl donors of opposite configuration. These reactions not only provide a new view of the catalytic capabilities of these supposedly strict hydrolases; they also furnish a basis for defining a detailed mechanism for catalysis. Present results, together with those of several recent studies from this laboratory (especially similar findings obtained with beta-amylase acting on alpha- and beta-maltosyl fluoride (Hehre, E. J., Brewer, C. F., and Genghof, D. S. (1979) J. Biol. Chem. 254, 5942-5950), provide strong new evidence for the functional flexibility of the catalytic groups of carbohydrases.