Elongation and insolubilisation of α-glucans by the action of Neisseria polysaccharea amylosucrase

Amylosucrase (E.C. 2.4.1.4) from Neisseria polysaccharea catalyses a transglycosylation reaction using sucrose as a glucose donor to synthesise an insoluble (1 --> 4)-alpha-glucan, releasing fructose in the solution. If glycogen is used as a glucosyl unit acceptor, amylosucrase elongates polymer branches from their non-reducing ends. Testing of a large series of acceptors with various molar masses, glycosidic linkages, branching degrees and solubilities showed that chain elongation occurred only on polymers with (1 --> 4)-alpha- or (1 --> 4)-alpha- and (1--> 6)-alpha- linkages. Synthesis yields were better for completely soluble polymers (1.45 glucosyl units grafted per glucosyl unit for polymers with (1 --> 4)-alpha- and (1 --> 6)-alpha- linkages), than for partially soluble polymers (0.27-0.97 glucosyl units grafted per glucosyl unit for polymers with either (1 --> 4)-alpha- linkages or (1 --> 4)-alpha- and (1 --> 6)-alpha- linkages). Elongation occurred randomly at the non-reducing ends of some external chains. Elongation of soluble branched molecules led to rapid gel formation favourable to gelation control inside suspensions and solutions. These polymers showed resistant starch contents (22% (w/w) to 57%) after elongation with amylosucrase. (C) 2004 Elsevier Ltd. All rights reserved.