The mechanism of acceptor reactions of leuconostoc mesenteroides B-512F dextransucrase

John F. Robyt, Timothy F. Walseth

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Reactions of dextransucrase and sucrose in the presence of sugars (acceptors) of low molecular weight have been observed to give a dextran of low molecular weight and a series of oligosaccharides. The acceptor reaction of dextransucrase was examined in the absence and presence of sucrose by using d-[14C]glucose, d-[14C]fructose, and 14C-reducing-end labeled maltose as acceptors. A purified dextransucrase was pre-incubated with sucrose, and the resulting d-fructose and unreacted sucrose were removed from the enzyme by chromatography on columns of Bio-Gel P-6. The enzyme, which migrated at the void volume, was collected and referred to as "charged enzyme". The charged enzyme was incubated with 14C-acceptor in the absence of sucrose. Each of the three acceptors gave two fractions of labeled products, a high molecular weight product, identified as dextran, and a product of low molecular weight that was an oligosaccharide. It was found that all three of the acceptors were incorporated into the products at the reducing end. Similar results were obtained when the reactions were performed in the presence of sucrose, but higher yields of labeled products were obtained and a series of homologous oligosaccharides was produced when d-glucose or maltose was the acceptor. We propose that the acceptor reaction proceeds by nucleophilic displacement of glucosyl and dextranosyl groups from a covalent enzyme-complex by a specific, acceptor hydroxyl group, and that this reaction effects a glycosidic linkage between the d-glucosyl and dextranosyl groups and the acceptor. We conclude that the acceptor reactions serve to terminate polymerization of dextran by displacing the growing dextran chain from the active site of the enzyme; the acceptors, thus, do not initiate dextran polymerization by acting as primers.

Original languageEnglish (US)
Pages (from-to)433-445
Number of pages13
JournalCarbohydrate Research
Issue number1
StatePublished - Mar 1978

Bibliographical note

Funding Information:
*Dedicated to Professor Dexter French, on the occasion of his 60th birthday and in recognition of his many contributions to the study of carbohydrate structure and the mechanisms of carbohydrase action. *Part IV in a series The Mechanism of Dextransucrase Action (see ref. 5 for Part III). Supported by Grant No. DE-03578 from the National Institute of Dental Research, National Institutes of Health, U.S. Public Health Service and taken in part from a thesis by T.F.W. submitted to Iowa State University, Ames, IA, in partial fulfillment of the requirements for the Ph.D. degree. Vresent address: Department of PhysiobgyB,n derbih UmverstZy N&hviIke, Tennessee 37202, a;s*_+_ .-


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