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Title: PENTA-, HEXA-, AND HEPTA-SACCHARIDE ACCEPTOR PRODUCTS OF ALTERNANSUCRASE

Author
item Cote, Gregory
item Sheng, Suzie

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2006
Publication Date: 5/23/2006
Citation: Cote, G.L., Sheng, S.S. 2006. Penta-, hexa-, and hepta-saccharide acceptor products of alternansucrase. Carbohydrate Research. 341:2066-2072.

Interpretive Summary: Fundamental information on the structures of novel sugar-based food ingredients is required in order to understand and predict their nutritional role and acitivity. In this paper, we isolate the major carbohydrate components from a novel sugar-derived food ingredient and determine their chemical structures. The products are fewer in number and more regular in structure than predicted by earlier mathematical modeling. These results tell us important facts about how the enzyme works. They also give us more information about the new ingredient, which may allow us to better understand how it is digested in the body. These results will be of interest to food ingredient manufacturers, food formulators, and researchers.

Technical Abstract: In the presence of suitable acceptor molecules, dextransucrase makes a homologous series of oligosaccharides in which the isomers differ by a single glucosyl unit, whereas alternansucrase synthesizes one trisaccharide, two tetrasaccharides, etc. For the example of maltose as the acceptor, if one considers only the linear, unbranched possibilities for alternansucrase, the hypothetical number of potential products increases exponentially as a function of degree of polymerization (DP). Experimental evidence indicates that far fewer products are actually formed. We show that only certain isomers of DP>4 are formed from maltose in measurable amounts, and that these oligosaccharides belong to the oligoalternan series rather than the oligodextran series. When the oligosaccharide acceptor products from maltose were separated by size-exclusion chromatography and HPLC, only one pentasaccharide was isolated. Its structure was alpha-D-Glcp(1'6)-alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'4)-D-Glc. Two hexasaccharides were formed in approximately equal quantities: alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'4)-D-Glc and alpha-D-Glcp(1'6)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'4)-D-Glc. Just one heptasaccharide was isolated from the reaction mixture, alpha-D-Glcp(1'6)-alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'3)-alpha-D-Glcp(1'6)-alpha-D-Glcp(1'4)-D-Glc. We conclude that the enzyme is incapable of forming two consecutive alpha(1'3) linkages, and does not form products with more than two consecutive alpha(1'6) linkages. The distribution of products may be kinetically determined.