Abstract
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.
Highlights
Rhizopus niveusglucoamylase and Arthrotxwterglobiformis glucodextranase, which catalyze the hydrolysis of starch and dextrans,respectively, to form D-glUCOSe of inverted (p) configuration, were found to convert occur without glycosidic bond cleavage has emerged as an effective means of gaining deeper understanding of the catalytic capabilities and mechanism of carbohydrases [1,2,3,4,5,6,7,8].For example, fresh insight was recently obtained into the funcboth a- and @-D-glucosylfluoride to B-D-glucose and tioning of P-amylase through the demonstration [7] that this hydrogen fluoride
Present but is shared by two D-glucosyl mobilizing exo-a-glucanases, results, together with those of several recent studies the glucoamylase of Rhizopus niveusand the glucodextranase from this laboratory. These enzymes catalyze reactained with @-amylase acting on a- and @-maltosyl tions with a- and /i-D-glucopyranosyl fluoride that are comfluoride
BioL Chem 254,5942-5950), provide strong with &amylase acting on a- and P-maltosyl fluoride
Summary
STEREOCOMPLEMENTARY HYDROLYTTC AND GLUCOSYL-TRANSFERRING ACTIONS OF GLUCOAMYLASE AND GLUCODEXTRANASE WITH a- AND ~-D-GLUCOSYLFLUORIDE*. Present but is shared by two D-glucosyl mobilizing exo-a-glucanases, results, together with those of several recent studies the glucoamylase of Rhizopus niveusand the glucodextranase from this laboratory These enzymes catalyze reactained with @-amylase acting on a- and @-maltosyl tions with a- and /i-D-glucopyranosyl fluoride that are comfluoride GM 25478-01 from the National Institute for General Medical Sciences.To whom reprint requests may be addressed at thDe epartment of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
