Relative, quantitative effects of acceptors in the reaction of Leuconostoc mesenteroides B-512F dextransucrase

Abstract

The acceptor reaction of dextransucrase consists of the transfer of d-glucosyl groups from sucrose to other carbohydrates, and occurs at the expense of dextran synthesis. In the present study, solutions of [14C]sucrose and of each of seventeen acceptor sugars were digested with highly purified Leuconostoc mesenteroides B-512F dextransucrase. The products were separated by paper chromatography, and quantitated by liquid scintillation counting. Maltose was the most effective acceptor; its products, members of an isomaltodextrinyl-maltose series (d.p. 3 to 6), accounted for >75% of the d-glucosyl groups of sucrose. Other acceptors giving rise to a similar series of oligosaccharide products were (in order of decreasing effectiveness): isomaltose, nigerose, methyl α-d-glucoside, 1,5-anhydro-d-glucitol, d-glucose, turanose, methyl β-d-glucoside, cellobiose, and l-sorbose. Lactose, raffinose, melibiose, d-galactose, and d-xylose each gave a single, mono-d-glucosylated product; d-fructose and d-mannose each gave a pair of mono-d-glucosylated (disaccharide) products. Another series of digests contained sucrose and various proportions of maltose. As the level of maltose increased, the size of the largest oligosaccharide acceptor-product decreased, and less dextran was produced. The virtual absence of high-d.p. (8 to 13) oligosaccharide products in all acceptor digests is interpreted as evidence against a role for acceptors as primers of dextran synthesis.