Submitted to: Carbohydrate Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/14/2003
Publication Date: 9/14/2003
Citation: Cote, G.L., Dunlap, C.A. 2003. Alternansucrase acceptor reactions with methyl hexopyranosides. Carbohydrate Research. 338:1961-1967. Interpretive Summary: Alternansucrase is an unusual enzyme from bacteria that makes a water-soluble gum from cane or beet sugar. It can also make small sugar molecules that show potential use as health-enhancing food and feed additives. This paper describes a basic study on the nature of the chemical reactions carried out by this enzyme and allows us to make predictions about the types of products it can make from various sugars. One observation is that alternansucrase is very different from and much better than the current commercial enzyme known as dextransucrase for carrying out these reactions.
Technical Abstract: Alternansucrase is a glucansucrase that synthesizes an alternating alpha-1,3 and 1,6-linked D-glucan from sucrose. It also synthesizes oligosaccharides via glucopyranosyl transfer to various acceptor sugars. We have studied the acceptor products arising from methyl glycosides as model compounds in order to better understand the specificity of alternansucrase acceptor reactions. The initial product arising from methyl alpha-D-glucopyranoside was methyl alpha-isomaltoside, which was subsequently glucosylated to yield methyl alpha-isomaltotrioside and methyl O-alpha-D-glucopyranosyl-(1-3)-O-alpha-D-glucopyranosyl-(1-6)-alpha-D-glucopyranoside. These products are analogous to those previously described from methyl alpha-D-glucopyranoside. The major initial acceptor product from methyl alpha-D-mannopyranoside was methyl O-alpha-D-glucopyranosyl-(1-6)-alpha-D-mannopyranoside, but several minor products were also isolated and characterized, including a 3,6-di-O-substituted mannopyranoside. Methyl alpha-D-galactopyranoside yielded two initial products, methyl O-alpha-D-glucopyranosyl-(1-3)-alpha-D-galactopyranoside and methyl O-alpha-D-glucopyranosyl-(1-4)-alpha-D-galactopyranoside, in a 2.5:1 molar ratio. Methyl D-allopyranosides were glucosylated primarily at position 6, yielding methyl O-alpha-D-glucopyranosyl-(1-6)-D-allopyranosides. The latter subsequently gave rise to methyl O-alpha-D-glucopyranosyl-(1-6)-O-alpha-D-glucopyranosyl-(1-6)-D-allopyranosides. In general, the methyl alpha-D-hexopyranosides were better acceptors than the corresponding beta-glycosides.