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Title: ALTERNANSUCRASE ACCEPTOR REACTIONS WITH D-TAGATOSE AND L-GLUCOSE

Author
item Cote, Gregory
item Dunlap, Christopher
item Appell, Michael
item Momany, Frank

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2004
Publication Date: 12/18/2004
Citation: Cote, G.L., Dunlap, C.A., Appell, M.D., Momany, F.A. 2005. Alternansucrase acceptor reactions with d-tagatose and l-glucose. Carbohydrate Research. 340:257-262.

Interpretive Summary: The reactions of the enzyme alternansucrase with sugar can produce a wide variety of complex carbohydrates. Some of these have recently been shown to have potential benefits for digestive health. This paper describes two such reactions and the chemical structures of the products. The reaction with L-glucose (a "left-handed sugar", or mirror image of the naturally occurring form) and computer analysis of the chemical structures may shed new light on the mode of action of this enzyme. The reaction with tagatose, a new commercial sweetener, yields a potentially useful new product that may find application as a food or feed supplement.

Technical Abstract: Alternansucrase (EC 2.4.1.140) is a D-glucansucrase that synthesizes an alternating alpha-(1-3),(1-6)-linked D-glucan from sucrose. It also synthesizes oligosaccharides via D-glucopyranosyl transfer to various acceptor sugars. Two of the more efficient monosaccharide acceptors are D-tagatose and L-glucose. In the presence of D-tagatose, alternansucrase produced the disaccharide alpha-D-glucopyranosyl-(1-1)-beta-D-tagatopyranose via glucosyl transfer. This disaccharide is analogous to trehalulose. We were unable to isolate a disaccharide product from L-glucose, but the trisaccharide alpha-D-glucopyranosyl-(1-6)-alpha-D-glucopyranosyl-(1-4)-L-glucose was isolated and identified. This is analogous to panose, one of the structural units of pullulan, in which the reducing-end D-glucose residue has been replaced by its L-enantiomer. The putative L-glucose disaccharide product, produced by glucoamylase hydrolysis of the trisaccharide, was found to be an acceptor for alternansucrase. The disaccharide, alpha-D-glucopyranosyl-(1-4)-L-glucose, was a better acceptor than maltose, previously the best known acceptor for alternansucrase. A structure comparison of alpha-D-glucopyranosyl-(1-4)-L-glucose and maltose was performed through computer modeling to identify common features which may be important in acceptor affinity by alternansucrase.