Author
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Cote, Gregory |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 1/11/2006 Publication Date: 7/28/2006 Citation: Cote, G.L. 2006. Penta-, hexa-, and hepta-saccharide acceptor products of alternansucrase [abstract]. International Carbohydrate Symposium. Paper No. PS69. Interpretive Summary: Technical Abstract: Dextransucrase and alternansucrase are bacterial enzymes that transfer glucosyl units from sucrose into long-chain polymers of glucose. In the presence of suitable acceptor molecules, glucosyl transfer can also occur to the acceptor, forming glucose-oligosaccharides of varying molecular size (degree of polymerization, DP). A major difference between commercial dextransucrase and alternansucrase is that dextransucrase makes a homologous series of oligosaccharides in which the isomers differ by a single glucosyl unit, whereas alternansucrase synthesizes one DP 3 product, two DP 4 products, 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 DP. Experimental evidence indicates that far fewer products are actually formed. It was shown previously that the enzyme does not synthesize an alpha(1'3) linkage by acceptor reactions unless an alpha(1'6) linkage is present, and that the enzyme is incapable of forming two consecutive alpha(1'3) linkages [2]. We will present data showing 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; they were 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 has been 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 more than two consecutive alpha(1'6) linkages. This provides useful information regarding the specificity and possible mechanisms of the enzyme action. This information is especially important in light of the fact that mixtures of these oligosaccharides are undergoing evaluation as food ingredients. These reactions represent novel synthetic routes to unusual oligosaccharides. |
